Hildegunn Viljugrein

• Mysterud, Atle; Rivrud, Inger Maren; Meisingset, Erling L.; Jore, Solveig & Viljugrein, Hildegunn (2025). Deer migration, deer density, tick distribution and incidence of a tick‐borne zoonosis. Journal of Animal Ecology. ISSN 0021-8790. 94(12), s. 2655–2670. doi: 10.1111/1365-2656.70163. Fulltekst i vitenarkiv Vis sammendrag

  1. Our understanding of how migratory wildlife populations affect incidence of in-fectious diseases spilling over into humans is limited. Ticks are expanding theirdistribution towards northern latitudes, causing emergence of tick- borne dis-eases. Deer serve as reproduction hosts for adult ticks, supporting the tick pop -ulations. However, in northern areas, deer populations are partially migratory,and migrants occupy high elevation summer ranges that are unsuitable for ticks.Migration can thus theoretically lead to escape from exposure to ticks and to deerfeeding fewer ticks, which lower disease hazard to humans. 2. Combining data on Ixodes ricinus tick abundance with GPS-tracking data of reddeer (Cervus elaphus), we quantified the distributional overlap of ticks and reddeer along elevational gradients in Norway. Furthermore, we correlated bothdeer density and the proportion of migratory deer with the incidence of Lymedisease in humans. 3. We found that migratory deer summer ranges had colder climate and overlappedless with tick distribution than those of resident deer. Deer density consistentlyincreased Lyme disease incidence in humans. However, we found only weak evi-dence that deer migration negatively affected Lyme disease incidence. 4. Our study provides a rare quantification of how host availability, in terms of bothhost density and migratory movement, affects risk of a zoonotic disease.

• Dean, Katharine Rose; Grøntvedt, Carl Andreas; Hopp, Petter; Viljugrein, Hildegunn & Wolff, Cecilia Mia (2025). Data quality assessment of pig movements in the Norwegian Livestock Register reveals challenges for outbreak preparedness. BMC Veterinary Research. 21(1). doi: 10.1186/s12917-025-04695-y. Fulltekst i vitenarkiv
• Stige, Leif Christian; Qviller, Lars; Viljugrein, Hildegunn & Tavornpanich, Saraya (2025). A salmon lice prediction model. Preventive Veterinary Medicine. ISSN 0167-5877. 235. doi: 10.1016/j.prevetmed.2024.106405. Fulltekst i vitenarkiv
• Mysterud, Atle; Osnes, Magnus Nygård; Dean, Katharine Rose; Widgren, Stefan; Tranulis, Michael A. & Viljugrein, Hildegunn (2025). Modelling the effect of genotype (PRNP) linked to susceptibility, infection duration and prion shedding on chronic wasting disease dynamics of cervids. Ecological Modelling. ISSN 0304-3800. 509. doi: 10.1016/j.ecolmodel.2025.111253. Fulltekst i vitenarkiv Vis sammendrag

  Host genetics affect their susceptibility to pathogens and their ability to transmit infections (contagiousness). Chronic wasting disease (CWD) is a lethal prion disease of cervids with a wide distribution in North America, and with the first detection in Europe among reindeer in Norway in 2016. The PRNP gene, encoding the prion protein, has a strong impact on host susceptibility, and the duration and level of prion shedding. We developed a Susceptible-Exposed-Infectious-Dead (SEID) model to enhance our understanding of how PRNP genotype variation influences CWD dynamics. In a baseline model with only highly susceptible PRNP alleles, CWD prevalence reached a high level before the population collapsed. We sequentially introduced PRNP heterogeneity in susceptibility (Scenario 1), the duration of prion shedding (Scenario 2), and amount of prion shedding (Scenario 3). Heterogeneity in susceptibility alone (Scenario 1) led to a slow increase in CWD prevalence towards its peak, followed by a gradual decline and eventual epidemic die-out. Increasing the infection duration with constant shedding for the less susceptible PRNP genotypes (Scenario 2) led to a high and persistent CWD-prevalence level. When combining low-susceptibility PRNP alleles and increased duration of shedding but at lower levels (Scenario 3), the prevalence of CWD peaked slowly compared to the other scenarios. Hence, variation in PRNP allele composition can yield qualitatively different CWD epidemics among populations. Our ability to predict the longterm effects of CWD remains limited, primarily due to uncertainty about shedding patterns, environmental contamination, and other factors associated with PRNP-alleles that may limit selection.

• Torget, Vidar; Bernhoft, Aksel; Müller, Mette Helen Bjørge; Polder, Anuschka; Viljugrein, Hildegunn & Madslien, Knut [Vis alle 7 forfattere av denne artikkelen] (2024). The red listed eagle owl (Bubo bubo) population in Norway is exposed to POP levels exceeding threshold values for adverse health effects. Environment International. ISSN 0160-4120. 186. doi: 10.1016/j.envint.2024.108650. Fulltekst i vitenarkiv
• Mysterud, Atle; Moorter, Bram Van; Viljugrein, Hildegunn; Andersen, Roy; Strand, Olav & Rolandsen, Christer Moe (2024). Evidence of limited short-term adverse demographic side effects of chronic wasting disease management. Journal of Wildlife Management. ISSN 0022-541X. doi: 10.1002/jwmg.22693. Fulltekst i vitenarkiv Vis sammendrag

  Competing objectives are common in the management of wildlife diseases. However, the extent to which disease mitigation conflicts with other goals has rarely been quantified. Chronic wasting disease (CWD) is a lethal cervid disease widely distributed in North America and recently detected in Europe. After the detection of CWD among reindeer (Rangifer tarandus) in Norway in 2016, intensified and male‐biased harvesting was used to manage CWD, but this may have adverse side effects. Based on extensive surveillance data (2001‒2022) gathered by the Norwegian Institute for Nature Research (NINA) and local management in addition to harvest statistics, we quantified how CWD management in Hardangervidda, Norway, changed harvest rates and affected population size, operational sex ratio, and age structure, and, in turn, whether recruitment, sex ratio of calves, and calving dates were affected. We used a formal reindeer quality standard to define adverse management. The estimated harvest rate of adult males reached >40% annually; however, the population size was only moderately reduced because the harvest of adult females was similar or decreased. The sex ratio changed from approximately 1:2.2 to 1:6.5 (males ≥3 years: females ≥1 year), which brought the population from good to poor quality according to the reindeer quality standard. The proportion of prime‐aged (≥5 years) males among adult males (≥2 years) in the harvest decreased from >60% to approximately 30%. Demographic changes led to limited side effects in the short‐term, with a delay of 4‒5 days in calving dates and a slightly more female‐biased sex ratio among the harvested calves but without a marked change in early recruitment. Wildlife populations are increasingly threatened by severe disease outbreaks that may require intensive management. Our study highlights the importance of extensive surveillance to document the potential adverse effects on population abundance, demography, and demographic side effects. The fairly limited short‐term adverse impacts can be traded against a higher likelihood of future sustainability without severe diseases; however, this may become an issue of concern if the disease becomes endemic. Balancing these trade‐offs would benefit from good communication between veterinary sciences and wildlife ecology experts. adverse side effects, cervids, environmental quality standard, Rangifer tarandus, reindeer, selective harvesting

• Lindsø, Lars; Viljugrein, Hildegunn & Mysterud, Atle (2024). Temporal increase in ticks and pathogen prevalence in the small mammal part of the Lyme disease cycle in northern Europe. Ecosphere. 15(11), s. 1–12. doi: 10.1002/ecs2.70063. Fulltekst i vitenarkiv Vis sammendrag

  Lyme disease is an emerging infectious disease and the most common vector-borne zoonosis in the northern hemisphere. The pathogen that causes Lyme disease in Europe is vectored by the generalist tick Ixodes ricinus, and the emergence of Lyme disease is partly linked to how climate warming affects tick distribution and abundance. However, we lack long-term data on tick infestations and infection prevalence in the main hosts involved in the transmission cycle. Here, we quantified the temporal trends (2014–2022) of I. ricinus infestations and the prevalence of Borrelia burgdorferi sensu lato in small mammalian hosts and linked annual variation to host abundance and climate in Norway. We found that tick infestations for both larvae (21% per year [95% CI 18–25]) and nymphs (18% [11–26]), and infection prevalence (14% [8–20]) increased over the period and were negatively associated with rodent abundance. Additionally, warmer years were associated with increased larval tick infestations on hosts. The combination of a temporal increase in both larval tick infestation and infection prevalence in hosts likely results in increased production of infected nymphs. Thus, we provide one mechanistic step toward understanding the Lyme disease emergence at northern latitudes of Europe. emerging infectious diseases, Lyme disease, small mammals, ticks

• Kvalnes, Thomas; Flagstad, Øystein; Våge, Jørn; Strand, Olav; Viljugrein, Hildegunn & Sæther, Bernt-Erik (2024). Harvest and decimation affect genetic drift and the effective population size in wild reindeer. Evolutionary Applications. 17(4). doi: 10.1111/eva.13684. Fulltekst i vitenarkiv Vis sammendrag

  Harvesting and culling are methods used to monitor and manage wildlife diseases. An important consequence of these practices is a change in the genetic dynamics of affected populations that may threaten their long-term viability. The effective population size (Ne) is a fundamental parameter for describing such changes as it determines the amount of genetic drift in a population. Here, we estimate Ne of a harvested wild reindeer population in Norway. Then we use simulations to investigate the genetic consequences of management efforts for handling a recent spread of chronic wasting disease, including increased adult male harvest and population decimation. The Ne/N ratio in this population was found to be 0.124 at the end of the study period, compared to 0.239 in the preceding 14 years period. The difference was caused by increased harvest rates with a high proportion of adult males (older than 2.5 years) being shot (15.2% in 2005–2018 and 44.8% in 2021). Increased harvest rates decreased Ne in the simulations, but less sex biased harvest strategies had a lower negative impact. For harvest strategies that yield stable population dynamics, shifting the harvest from calves to adult males and females increased Ne. Population decimation always resulted in decreased genetic variation in the population, with higher loss of heterozygosity and rare alleles with more severe decimation or longer periods of low population size. A very high proportion of males in the harvest had the most severe consequences for the loss of genetic variation. This study clearly shows how the effects of harvest strategies and changes in population size interact to determine the genetic drift of a managed population. The long-term genetic viability of wildlife populations subject to a disease will also depend on population impacts of the disease and how these interact with management actions.

• Lindsø, Lars; Viljugrein, Hildegunn & Mysterud, Atle (2024). Vector competence of Ixodes ricinus instars for the transmission of Borrelia burgdorferi sensu lato in different small mammalian hosts. Parasites & Vectors. 17(1), s. 1–10. doi: 10.1186/s13071-023-06110-7. Fulltekst i vitenarkiv Vis sammendrag

  Background Many pathogens and parasites can infect multiple host species, and the competence of different hosts as pathogen reservoirs is key to understanding their epidemiology. Small mammals are important hosts for the instar stages of Ixodes ricinus ticks, the principal vector of Lyme disease in Europe. Small mammals also act as reservoirs of Borrelia afzelii, the most common genospecies of the Borrelia burgdorferi sensu lato (s.l.) spirochetes causing Lyme disease in Europe. However, we lack quantitative estimates on whether different small mammal species are equally suitable hosts for feeding I. ricinus and whether they show differences in pathogen transmission from host to tick. Methods Here, we analysed the feeding success and prevalence of B. burgdorferi s.l. infections in 12,987 instar I. ricinus found on captured small mammals with known infection status in Norway (2018–2022). Results We found that larvae were more likely to acquire a blood meal from common shrews (Sorex araneus, 46%) compared to bank voles (Myodes glareolus, 36%) and wood mice (Apodemus sylvaticus, 31%). Nymphs tended to be more likely to acquire a blood meal from wood mice (66%) compared to bank voles (54%). Common shrews harboured few nymphs (n=19). Furthermore, we found that larvae feeding on infected bank voles (11%) were more likely to be infected with B. burgdorferi s.l. than larvae on infected common shrews (7%) or wood mice (4%). Conclusions Our study provides quantitative evidence of differences in suitability for the instar stages of I. ricinus across taxa of small mammals and highlights how even known small mammal host species can differ in their ability to feed ticks and infect larval ticks with the pathogen causing Lyme disease. Graphical Abstract

• Baron, Jerome N.; Mysterud, Atle; Hopp, Petter; Rosendal, Thomas; Frössling, Jenny & Benestad, Sylvie L. [Vis alle 9 forfattere av denne artikkelen] (2024). Assessing freedom from chronic wasting disease in semi-domesticated reindeer in Norway and Sweden. Preventive Veterinary Medicine. ISSN 0167-5877. 229. doi: 10.1016/j.prevetmed.2024.106242. Fulltekst i vitenarkiv Vis sammendrag

  Establishing freedom from disease is a key component of surveillance and may have direct consequences for trade and economy. Transboundary populations pose challenges in terms of variable legislation, efforts, and data availability between countries, often limiting surveillance efficiency. Chronic wasting disease (CWD) is a contagious prion disease of cervids. The long incubation period and slow initial epidemic growth make it notoriously difficult to detect CWD in the early phase of an epidemic. The recent emergence of CWD in wild reindeer in Norway poses a threat to approximately 250,000 semi-domesticated reindeer in Norway and 250,000 in Sweden, including transboundary populations. Here, we provide a first analysis of surveillance data (2016–2022) from all reindeer districts in Norway and Sweden to determine the probability of freedom from CWD infection. During the six years, 6017 semi-domesticated reindeer were tested in Sweden and 51,974 in Norway. Most samples came from healthy slaughtered animals (low risk). Reindeer use large and remote areas and (high risk) samples from fallen stock and animals with clinical signs were difficult to obtain. A scenario tree model was run for seven different set of values for the input parameters (design prevalence within and between districts, probability of introduction, and relative risks) to determine the effect on surveillance sensitivity. At the national level, the mean probability of disease freedom was 59.0 % in Sweden and 87.0 % in Norway by 2021. The most marked effect on sensitivity was varying the design prevalence both within and between districts. Uncertainty about relative risk ratios affected sensitivity for Sweden more than for Norway, due to the higher proportion of animals in the high-risk group in the former (13.8 % vs. 2.1 %, respectively). A probability of disease freedom of 90 % or higher was reached in 8.2 % of the 49 districts in Sweden and 43.5 % of the 46 districts in Norway for a design prevalence of 0.5 %. The probability of freedom remained below 60 % in 29 districts (59.2 %) in Sweden and 10 districts (21.7 %) in Norway. At the national level, only Norway had a sufficiently large number of samples to reach a probability of more than 95 % of disease freedom within a period of 10 years. Our cross-border assessment forms an important knowledge base for designing future surveillance efforts depending on the spatial pattern of prevalence of CWD and risk of spread.

• Jore, Solveig; Viljugrein, Hildegunn; Hjertqvist, Marika; Dub, Timothée & Mäkelä, Henna (2023). Outdoor recreation, tick borne encephalitis incidence and seasonality in Finland, Norway and Sweden during the COVID-19 pandemic (2020/2021). Infection Ecology & Epidemiology. 13(1), s. 1–12. doi: 10.1080/20008686.2023.2281055. Fulltekst i vitenarkiv Vis sammendrag

  During the pandemic outdoor activities were encouraged to mitigate transmission risk while providing safe spaces for social interactions. Human behaviour, which may favour or disfavour, contact rates between questing ticks and humans, is a key factor impacting tick-borne encephalitis (TBE) incidence. We analyzed annual and weekly TBE cases in Finland, Norway and Sweden from 2010 to 2021 to assess trend, seasonality, and discuss changes in human tick exposure imposed by COVID-19. We compared the pre-pandemic incidence (2010–2019) with the pandemic incidence (2020–2021) by fitting a generalized linear model (GLM) to incidence data. Pre-pandemic incidence was 1.0, 0.29 and 2.8 for Finland, Norway and Sweden, respectively, compared to incidence of 2.2, 1.0 and 3.9 during the pandemic years. However, there was an increasing trend for all countries across the whole study period. Therefore, we predicted the number of cases in 2020/2021 based on a model fitted to the annual cases in 2010–2019. The incidences during the pandemic were 1.3 times higher for Finland, 1.7 times higher for Norway and no difference for Sweden. When social restrictions were enforced to curb the spread of SARS-CoV-2 there were profound changes in outdoor recreational behavior. Future consideration of public health interventions that promote outdoor activities may increase exposure to vector-borne diseases.

• Lindsø, Lars; Anders, Jason Lee; Viljugrein, Hildegunn; Herland, Anders; Stigum, Vetle Malmer & Easterday, William Ryan [Vis alle 7 forfattere av denne artikkelen] (2023). Individual heterogeneity in ixodid tick infestation and prevalence of Borrelia burgdorferi sensu lato in a northern community of small mammalian hosts. Oecologia. ISSN 0029-8549. 203(3), s. 421–433. doi: 10.1007/s00442-023-05476-w. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Heterogeneous aggregation of parasites between individual hosts is common and regarded as an important factor in understanding transmission dynamics of vector-borne diseases. Lyme disease is vectored by generalist tick species, yet we have a limited understanding of how individual heterogeneities within small mammal host populations affect the aggregation of ticks and likelihood of infection. Male hosts often have higher parasite and infection levels than females, but whether this is linked to sexual body size dimorphism remains uncertain. Here, we analysed how host species, sex, and body mass influenced Ixodes ricinus tick infestations and the infection prevalence of Borrelia burgdorferi sensu lato (s.l.) in three species of small mammals involved in the enzootic transmission cycle of Lyme disease in Norway from 2018 to 2022. Larval and nymphal ticks were found on 98% and 34% of all individual hosts, respectively. In bank voles and wood mice, both larval and nymphal tick infestation and infection probability increased with body mass, and it increased more with mass for males than for females. Tick infestation in the common shrew increased with body mass and was higher in males, while pathogen infection was higher in females. Sex-biases in infestation did not correspond with level of sexual body mass dimorphism across species. This study contributes to our understanding of how individual heterogeneity among small mammalian hosts influences I. ricinus tick aggregation and prevalence of B. burgdorferi s.l. at northern latitudes.

• Goren, Asena; Viljugrein, Hildegunn; Rivrud, Inger Maren; Jore, Solveig; Bakka, Haakon & Vindenes, Yngvild [Vis alle 7 forfattere av denne artikkelen] (2023). The emergence and shift in seasonality of Lyme borreliosis in Northern Europe. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 290(1993). doi: 10.1098/rspb.2022.2420. Fulltekst i vitenarkiv Vis sammendrag

  Climate change has had a major impact on seasonal weather patterns, resulting in marked phenological changes in a wide range of taxa. However, empirical studies of how changes in seasonality impact the emergence and seasonal dynamics of vector-borne diseases have been limited. Lyme borreliosis, a bacterial infection spread by hard-bodied ticks, is the most commonvector-borne disease in the northern hemisphere and has been rapidly increasing in both incidence and geographical distribution in many regions of Europe and North America. By analysis of long-term surveillance data (1995–2019) from across Norway (latitude 57°580–71°080 N), we demonstrate a marked change in the within-year timing of Lyme borreliosis cases accompanying an increase in the annual number of cases. The seasonal peak in cases is now six weeks earlier than 25 years ago, exceeding seasonal shifts in plant phenology and previous model predictions. The seasonal shift occurred predominantly in the first 10 years of the study period. The concurrent upsurgence in case number and shift in case timing indicate a major change in the Lyme borreliosis disease system over recent decades. This study highlights the potential for climate change to shape the seasonal dynamics of vector-borne disease systems. seasonality, vector-borne zoonoses,disease ecology, Lyme borreliosis,Lyme disease, climate change, ecology, health and disease and epidemiology

• Goren, Asena; Mysterud, Atle; Jore, Solveig; Viljugrein, Hildegunn; Bakka, Haakon & Vindenes, Yngvild (2023). Demographic patterns in Lyme borreliosis seasonality over 25 years. Zoonoses and Public Health. ISSN 1863-1959. 70(7), s. 647–655. doi: 10.1111/zph.13073. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Lyme borreliosis, the most common vector‐borne disease in Europe and North America, is attracting growing concern due to its expanding geographic range. The growth in incidence and geographic spread is largely attributed to climate and land‐use changes that support the tick vector and thereby increase disease risk. Despite a wide range of symptoms displayed by Lyme borreliosis patients, the demographic patterns in clinical manifestations and seasonal case timing have not been thoroughly investigated and may result from differences in exposure, immunity and pathogenesis. We analysed 25 years of surveillance data from Norway, supplemented by population demography data, using a Bayesian modelling framework. The analyses aimed to detect differences in case seasonality and clinical manifestations of Lyme borreliosis across age and sex differentiated patient groups. The results showed a bimodal pattern of incidence over age, where children (0–9 years) had the highest incidence, young adults (20–29 years) had low incidence and older adults had a second incidence peak in the ages 70–79 years. Youth (0–19 years) presented with a higher proportion of neuroborreliosis cases and a lower proportion of arthritic manifestations compared to adults (20+ years). Adult males had a higher overall incidence than adult females and a higher proportion of arthritis cases. The seasonal timing of Lyme borreliosis consistently occurred around 4.4 weeks earlier in youth compared to adults, regardless of clinical manifestation. All demographic groups exhibited a shift towards an earlier seasonal timing over the 25‐year study period, which appeared unrelated to changes in population demographics. However, the disproportionate incidence of Lyme borreliosis in seniors requires increased public awareness and knowledge about this high‐risk group as the population continues to age concurrently with disease emergence. Our findings highlight the importance of considering patient demographics when analysing the emergence and seasonal patterns of vector‐borne diseases using long‐term surveillance data.

• Mysterud, Atle; Viljugrein, Hildegunn; Andersen, Roy; Rauset, Geir Rune; Reiten, Malin Rokseth & Rolandsen, Christer Moe [Vis alle 7 forfattere av denne artikkelen] (2023). An infectious disease outbreak and increased mortality in wild alpine reindeer. Ecosphere. 14(3), s. 1–10. doi: 10.1002/ecs2.4470. Fulltekst i vitenarkiv Vis sammendrag

  Climate changes may lead to tipping points where the epidemiologicalcharacteristics of infectious wildlife diseases suddenly change, leading tooutbreaks. However, empirically documented cases of the extent to whichemerging infectious diseases (EIDs) affect populations of large vertebrates arefew, partly because of the limited surveillance of remote wildlife populations.EIDs may potentially lead to higher mortality than mean mortality levels. Here,we quantified the likely impact of digital necrobacillosis on the survivaland population dynamics of wild alpine reindeer (Rangifer tarandus)inHardangervidda National Park (NP), Norway. The outbreak of digitalnecrobacillosis in 2019 contributed to a decrease in the summer survival rate ofjuveniles to 51% compared to an average of 88% in 2005–2018 and 77% in 2020.However, since the outbreak mainly reduced juvenile survival, the impact onshort-term population dynamics was moderate, lowering the population growthrate (λ) before harvest from an average value of 1.18 (2005–2018) to 1.08 (2019)before harvest. In 2019, anomalous climate conditions with a high daily meantemperature combined with the highest recorded daily precipitation in late sum-mer were observed. Further studies are required to document the pathologicaldevelopment of digital necrobacillosis across demographic groups and proximateand ultimate causes of mortality. demography, digital necrobacillosis, disease ecology, National Park, population dynamics,reindeer, surviva

• Mysterud, Atle; Viljugrein, Hildegunn; Hopp, Petter; Andersen, Roy; Bakka, Haakon & Benestad, Sylvie L. [Vis alle 14 forfattere av denne artikkelen] (2023). Challenges and opportunities using hunters to monitor chronic wasting disease among wild reindeer in the digital era. Ecological Solutions and Evidence. 4(1). doi: 10.1002/2688-8319.12203. Fulltekst i vitenarkiv Vis sammendrag

  1. Surveillance of wildlife diseases poses considerable logistical challenges com-pared to that of humans or livestock. Citizen science can enable broader cover-age, but building an efficient disease monitoring system that relies on hunters is challenging. Chronic wasting disease (CWD) is a lethal and infectious prion dis-ease of cervids. Improving surveillance is important with the detection of CWD in wild reindeer (Rangifer tarandus) in Norway.2. This study describes the components of an efficient CWD monitoring sys-tem utilizing recreational hunters. We report the success of data capture after 6 years of surveillance. We provide an overview of CWD occurrence among the 24 wild reindeer areas and quantify the likelihood of disease absence in areas without detection.3. Surveillance aimed to test hunted reindeer aged ≥1 year. With higher quotas and extended hunting seasons, proactive surveillance was implemented in at-risk areas. There were several challenges of population demarcation and the lack of surveys required for risk- based sampling. Several specific tools for hunters have been developed, including digital apps for rapid reporting and feedback. Laboratory capacity was expanded, and novel statistical tools were developed for the specifics of the sampled tissues.4. The surveillance (2016–2021) achieved a sample return rate of 61.5% from a maximum of 22,123 harvested reindeer aged ≥1 year. Among these, 64.1% in-cluded both relevant tissues (retropharyngeal lymph nodes and brain), yielding 9412 (42.5%) complete samples of harvested reindeer. Samples originating from harvest constituted ~84% of total wild reindeer samples. 5. CWD was detected in 2 of the 24 wild reindeer management areas. The re-maining populations had a probability of CWD-freedom from 60% to 99% (mean= 77%) at a design prevalence of 0.5%.6. Utilizing hunters to monitor wildlife disease appears to be the most realistic op-tion for cervid species. However, the logistical and economic constraints are substantial and pose long-term challenges. Considerable uncertainty about dis-ease occurrence remains even after massive surveillance, and whether manage-ment should take preventive actions remains a challenge.cervids, citizen science, disease control, disease surveillance, freedom-from-disease, hunters, logistics, tissue sampling

• Aamelfot, Maria; Fosse, Johanna Hol; Viljugrein, Hildegunn; Ploss, Frieda Betty; Benestad, Sylvie L. & McBeath, Alastair [Vis alle 9 forfattere av denne artikkelen] (2022). Destruction of the vascular viral receptor in infectious salmon anaemia provides in vivo evidence of homologous attachment interference. PLoS Pathogens. ISSN 1553-7366. 18(10). doi: 10.1371/journal.ppat.1010905. Fulltekst i vitenarkiv
• Stige, Leif Christian; Helgesen, Kari Marie Olli; Viljugrein, Hildegunn & Qviller, Lars (2022). Modelling salmon lice-induced mortality of wild salmon post-smolts is highly sensitive to calibration data. Aquaculture Environment Interactions. ISSN 1869-215X. 14, s. 263–277. doi: 10.3354/aei00443. Fulltekst i vitenarkiv
• Mysterud, Atle; Hügli, Christian & Viljugrein, Hildegunn (2021). Tick infestation on medium–large-sized mammalian hosts: are all equally suitable to Ixodes ricinus adults? Parasites & Vectors. 14(1), s. 1–6. doi: 10.1186/s13071-021-04775-6. Fulltekst i vitenarkiv Vis sammendrag

  Background In Europe, the generalist tick, Ixodes ricinus, is the main vector of several tick-borne pathogens causing diseases in humans and livestock. Understanding how different species of hosts limit the tick population is crucial for management. In general, larger ectoparasites are expected to select hosts with larger body size. Consistent with this, larval and nymphal I. ricinus can feed on a wide range of different-sized vertebrates, while the adult female stage is expected to rely on a medium–large-sized host for reproduction. However, we still have a limited understanding of whether medium-sized hosts other than roe deer can serve as hosts to adult ticks, and other factors than size may also affect host selection. Methods To increase our understanding of the suitability of the different species of medium-sized hosts for adult ticks, we sampled mainly roadkill mammals from within the questing season of ticks. We counted life stages of ticks on roe deer (Capreolus capreolus) (n = 29), red fox (Vulpes vulpes) (n = 6), badger (Meles meles) (n = 14) and red squirrel (Sciurus vulgaris) (n = 17) from spatially overlapping populations in Norway, and analysed variation between species across different body parts with a mixed-effects negative binomial model (with and without zero-inflation). Results Red squirrel hosted a high density of larval and nymphal I. ricinus, but only one individual had adult female ticks. Roe deer hosted by far the largest number of adult ticks. Badgers had very few ticks, possibly due to their thick skin. Red foxes had intermediate numbers, but a high proportion of subcutaneous, dead ticks (69.3%), suggesting they are not very suitable hosts. Body mass predicted the presence of adult I. ricinus ticks. However, species was a better predictor than body mass for number of ticks, suggesting there was species variation in host suitability beyond body mass per se. Conclusions Our study provides evidence that roe deer are indeed the main suitable reproduction host to adult I. ricinus ticks, and are likely a key to host limitation of the tick population in this northern ecosystem. Graphic abstract

• Urke, H.A.; Daae, K.; Viljugrein, H.; Kandal, I.; Staalstrøm, A. & Jansen, P.A. (2021). Improvement of aquaculture management practice by integration of hydrodynamic modelling. Ocean and Coastal Management. ISSN 0964-5691. 213. doi: 10.1016/j.ocecoaman.2021.105849. Fulltekst i vitenarkiv Vis sammendrag

  Aquaculture has grown to become an important export industry in Norway. The Norwegian Food Safety Authorithy (NFSA) is responsible for the management of the production zones designated to aquaculture. Fish diseases and fish parasites are among the main threats to the aquaculture industry. It is therefore of great interest to minimize the risk of fish disease agent transmission. To date, the NFSA has assigned specific subzone divisions for aquaculture installations without assessing the effects of water contact for larger areas. Transmission of infection by water contact is believed to predominate the dispersal of important fish pathogens such as salmon pancreas disease virus (SPDV), infectious salmon anaemia (ISA) virus, Aeromonas salmonicida bacterias (held efficiently under control now by effective vaccines and not a major problem), and salmon lice. In this article we present a three-dimensional hydrodynamic model system (AquaStrøm) which gives detailed information about a network of 48 fish farm sites with varying degrees of mutual water contact in a Norwegian fjord area (the Nordfjord). By adding information on winds and currents, a better understanding of the mechanisms for the risk of transmission of fish disease agent between fish farms is gained. The risk of infection can be assessed in much more detail, and the production zones can be designed and optimized based on the level of water contact between various clusters of fish farms. Key sites which connect clusters of fish farms and hence increase the areas of mutual water contact can be identified.

• Stige, Leif Christian; Helgesen, Kari Marie Olli; Viljugrein, Hildegunn & Qviller, Lars (2021). A statistical mechanistic approach including temperature and salinity effects to improve salmon lice modelling of infestation pressure. Aquaculture Environment Interactions. ISSN 1869-215X. 13, s. 339–361. doi: 10.3354/aei00410. Fulltekst i vitenarkiv
• Viljugrein, Hildegunn; Hopp, Petter; Benestad, Sylvie L.; Våge, Jørn & Mysterud, Atle (2021). Risk-based surveillance of chronic wasting disease in semi-domestic reindeer. Preventive Veterinary Medicine. ISSN 0167-5877. 196. doi: 10.1016/j.prevetmed.2021.105497. Fulltekst i vitenarkiv Vis sammendrag

  Reindeer pastoralism is a widespread practise across Fennoscandia and Russia. An outbreak of chronic wasting disease (CWD) among wild reindeer (Rangifer tarandus) poses a severe threat to the semi-domestic reindeer herding culture. Establishing surveillance is therefore key, but current models for surveillance of CWD are designed for wild cervids and rely on samples obtained from recreational hunters. Targeting animal groups with a higher infection probability is often used for more efficient disease surveillance. CWD has a long incubation period of 2–3 years, and the animals show clinical signs in the later stages of the infection i.e. 1 Chronic wasting disease (CWD) Disease management Freedom from infection Policy Proactive management Prion protein gene (PRNP)

• Belsare, Aniruddha V.; Millspaugh, Joshua J.; Mason, J.Russ; Sumners, Jason; Viljugrein, Hildegunn & Mysterud, Atle (2021). Getting in front of chronic wasting disease: Model-informed proactive approach for managing an emerging wildlife disease. Frontiers in Veterinary Science. 7, s. 1–6. doi: 10.3389/fvets.2020.608235. Fulltekst i vitenarkiv Vis sammendrag

  Continuing geographic spread of chronic wasting disease (CWD) poses a serious threat to the sustainable future of cervids and hunting in North America. Moreover, CWD has been detected in captive cervids in South Korea and, in recent years, in free-ranging reindeer in Europe (Norway). Management of this disease is limited by logistical, financial, and sociopolitical considerations, and current strategies primarily focus on reducing host densities through hunter harvest and targeted culling. The success of such strategies in mitigating the spread and prevalence of CWD only upon detection is questionable. Here, we propose a proactive approach that emphasizes pre-emptive management through purposeful integration of virtual experiments (simulating alternate interventions as model scenarios) with the aim of evaluating their effectiveness. Here, we have used a published agent-based model that links white-tailed deer demography and behavior with CWD transmission dynamics to first derive a CWD outbreak trajectory and then use the trajectory to highlight issues associated with different phases of the CWD outbreak (pre-establishment/transition/endemic). Specifically, we highlight the practical constraints on surveillance in the pre-establishment phase and recommend that agencies use a realistic detection threshold for their CWD surveillance programs. We further demonstrate that many disease introductions are “dead ends” not leading to a full epidemic due to high stochasticity and harvesting in the pre-establishment phase of CWD. Model evaluated pre-emptive (pre-detection) harvest strategies could increase the resilience of the deer population to CWD spread and establishment. We conclude it is important to adaptively position CWD management ahead of, rather than behind, the CWD front.

• Krauer, Fabienne; Viljugrein, Hildegunn & Dean, Katharine Rose (2021). The influence of temperature on the seasonality of historical plague outbreaks. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 288(1954), s. 1–9. doi: 10.1098/rspb.2020.2725. Fulltekst i vitenarkiv Vis sammendrag

  Modern plague outbreaks exhibit a distinct seasonal pattern. By contrast, the seasonality of historical outbreaks and its drivers has not been studied systematically. Here, we investigate the seasonal pattern, the epidemic peak timing and growth rates, and the association with latitude, temperature, and precipitation using a large, novel dataset of plague- and all-cause mortality during the Second Pandemic in Europe and the Mediterranean. We show that epidemic peak timing followed a latitudinal gradient, with mean annual temperature negatively associated with peak timing. Based on modern temperature data, the predicted epidemic growth of all outbreaks was positive between 11.7°C and 21.5°C with a maximum around 17.3°C. Hence, our study provides evidence that the growth of plague epidemics across the whole study region depended on similar absolute temperature thresholds. Here, we present a systematic analysis of the seasonality of historical plague in the Northern Hemisphere, and we show consistent evidence for a temperature-related process influencing the epidemic peak timing and growth rates of plague epidemics.

• Handeland, Kjell; Tunheim, Ketil; Madslien, Knut Ivar Engesæter; Vikøren, Turid; Viljugrein, Hildegunn & Mossing, Anders [Vis alle 9 forfattere av denne artikkelen] (2021). High winter loads of Oestrid larvae and Elaphostrongylus rangiferi are associated with emaciation in wild reindeer calves. International Journal for Parasitology: Parasites and Wildlife. 15, s. 214–224. doi: 10.1016/j.ijppaw.2021.05.008. Fulltekst i vitenarkiv Vis sammendrag

  The Oestrid flies Cephemyia trompe and Hypoderma tarandi and the nematode Elaphostrongylus rangiferi are important parasites of Rangifer spp. The larvae of Oestrid flies develop in the throat (C. trompe) and skin (H. tarandi) of their host during winter while E. rangiferi develop in the CNS. Oestrid pupation, and development of E. rangiferi larvae from first- (L1) to infective third- stage in the environment during summer are highly temperature dependent. We investigated the possible negative effects of these parasites on the winter bodycondition of wild reindeer calves. Two year-classes (generations) of calf, born in a warm (2014) and cold (2015) summer respectively, were examined for changes in body condition between autumn and spring, in relation to the parasite load determined in the spring. The body condition in the autumn was assessed as carcass weight, while the body condition in the spring was assessed as carcass weight, supplemented by an evaluation of fat reserves in various bodily locations. Oestrids were counted directly whereas the E. rangiferi quantification was based on faecal counts of L1 larvae. The abundance of infections for Oestrids and E. rangiferi were significantly greater in the 2014 generation than in the 2015 generation. The mean carcass weight decreased between autumn and spring for the 2014 generation but increased in the 2015 generation. Emaciation in the spring was documented (fat reserve evaluation) in 42% and 7% of calves in the 2014 and 2015 cohorts, respectively. There was a significant correlation between high parasite load and the probability of emaciation. The mean summer temperature in 2014 was 2.6 ◦C higher than the mean for 2015, and 1.0 ◦C higher than the mean for the last 30- years. Our findings suggest that following a warm summer, high loads of Oestrids and E. rangiferi may cause emaciation and potentially deaths among the calves. Elaphostrongylus rangiferi Cephenemyia trompe Hypoderma tarandi Wild reindeer Climate Ecology

• Mysterud, Atle; Viljugrein, Hildegunn; Rolandsen, Christer Moe & Belsare, Aniruddha V. (2021). Harvest strategies for the elimination of low prevalence wildlife diseases. Royal Society Open Science. 8(3), s. 1–13. doi: 10.1098/rsos.210124. Fulltekst i vitenarkiv Vis sammendrag

  The intensive harvesting of hosts is often the only practicable strategy for controlling emerging wildlife diseases. Several harvesting approaches have been explored theoretically with the objective of lowering transmission rates, decreasing the transmission period or specifically targeting spatial disease clusters or high-risk demographic groups. Here, we present a novel model-based approach to evaluate alternative harvest regimes, in terms of demographic composition and rates, intended to increase the probability to remove all infected individuals in the population during the early phase of an outbreak. We tested the utility of the method for the elimination of chronic wasting disease based on empirical data for reindeer (Rangifer tarandus) in Norway, in populations with (Nordfjella) and without (Hardangervidda) knowledge about exact disease prevalence and population abundance. Low and medium harvest intensities were unsuccessful in eliminating the disease, even at low prevalence. High-intensity harvesting had a high likelihood of eliminating the disease, but probability was strongly influenced by the disease prevalence. We suggest that the uncertainty about disease prevalence can be mitigated by using an adaptive management approach: forecast from models after each harvest season with updated data, derive prevalence estimates and forecast further harvesting. We identified the problems arising from disease surveillance with large fluctuations in harvesting pressure and hence sample sizes. The elimination method may be suitable for pathogens that cause long-lasting infections and with slow epidemic growth, but the method should only be attempted if there is a low risk of reinfection, either by a new disease introduction event (e.g. dispersing hosts) or due to environmental reservoirs. Our simulations highlighted the short time window when such a strategy is likely to be successful before approaching near complete eradication of the population. chronic wasting disease, selective harvesting, reindeer, Norway, adaptive management

• Mysterud, Atle; Viljugrein, Hildegunn; Lund, Jan Henning L’Abée; Lund, Svein Erik; Rolandsen, Christer Moe & Strand, Olav (2021). The relationship between quotas and harvest in the alpine reindeer population on Hardangervidda, Norway. European Journal of Wildlife Research. ISSN 1612-4642. 67(6), s. 1–11. doi: 10.1007/s10344-021-01542-x. Fulltekst i vitenarkiv Vis sammendrag

  Hunting of cervids is commonly regulated by quotas that are specific to sex and age groups. There is substantial cultural variation in how quotas are regulated. In Scandinavia, the entire quotas are often not shot making deer management potentially less predictable. However, the effect of quota size and demographic composition on harvest offtake by recreational hunters has, to a limited extent, been empirically investigated in Scandinavia. Hunters are limited by time and opportunity and may not respond to changes in quota, as anticipated by managers. We analysed the variation in the proportion of quotas filled depending on quota size relative to population size and demographic composition of quotas during the period of 1986–2019 involving a population size varying from approximately 5000 to 15,000 reindeer on Hardangervidda, Norway. We found that the proportion of quota being filled by hunters varied substantially (12–48%) on an annual basis. The quota occasionally exceeded the estimated population size, but the proportion of the quota filled increased the higher the population size was relative to the quota size. The proportion of quota being filled by hunters was markedly lower for calf licences. High annual variation in the proportion of quota being filled by hunters causes considerable implementation uncertainty when managers aim to regulate cervid populations. Nevertheless, there was a strong correlation between quota size and harvest size. Facing new management requirements, a harvest rate of ~ 47% of the adult male population size was achieved in 2019, compared to an average of 16%. Hence, managers compensated for the low proportion of quota being filled by increasing quotas to reach target harvesting aims, but there remains a limit as to how precisely such a wide-ranging reindeer population can be regulated using recreational hunters.

• Mysterud, Atle; Hopp, Petter; Alvseike, Kristin Ruud; Benestad, Sylvie L.; Nilsen, Erlend Birkeland & Rolandsen, Christer Moe [Vis alle 9 forfattere av denne artikkelen] (2020). Hunting strategies to increase detection of chronic wasting disease in cervids. Nature Communications. 11, s. 1–11. doi: 10.1038/s41467-020-18229-7. Fulltekst i vitenarkiv Vis sammendrag

  The successful mitigation of emerging wildlife diseases may involve controversial host culling. For livestock, ‘preemptive host culling’ is an accepted practice involving the removal of herds with known contact to infected populations. When applied to wildlife, this proactive approach comes in conflict with biodiversity conservation goals. Here, we present an alternative approach of ‘proactive hunting surveillance’ with the aim of early disease detection that simultaneously avoids undesirable population decline by targeting demographic groups with (1) a higher likelihood of being infected and (2) a lower reproductive value. We applied this harvesting principle to populations of reindeer to substantiate freedom of chronic wasting disease (CWD) infection. Proactive hunting surveillance reached 99% probability of freedom from infection (<4 reindeer infected) within 3–5 years, in comparison to ~10 years using ordinary harvest surveillance. However, implementation uncertainties linked to social issues appear challenging also with this kind of host culling

• Madslien, Knut Ivar Engesæter; Stubsjøen, Solveig Marie; Viljugrein, Hildegunn; Ytrehus, Bjørnar; Solberg, Erling Johan & Kapronczai, Luciene [Vis alle 10 forfattere av denne artikkelen] (2020). Hair cortisol concentration and body mass in moose (Alces alces) infested with deer keds (Lipoptena cervi). Journal of Wildlife Diseases. ISSN 0090-3558. 56(3), s. 687–692. doi: 10.7589/2019-07-185. Fulltekst i vitenarkiv Vis sammendrag

  The deer ked (<i>Lipoptena cervi</i>), a hematophagous ectoparasite of cervids, is currently spreading in Scandinavia, and the moose (<i>Alces alces</i>) is its main host. However, little is known about the impact of deer keds on moose. We analyzed the hair cortisol concentration (HCC) from 262 moose harvested in the fall in relation to age class, sex, body mass (BM), and deer ked infestation intensity, and BM in relation to age class, sex, and infestation intensity. We found that HCC decreased with increasing deer ked intensity at low ked intensities, but for the higher levels of ked intensities, there was a positive relationship between HCC and ked intensity. The HCC was higher in males than in females and lower in yearlings than in calves and adults. Our failure to find any association between BM and deer ked intensity suggested a negligible impact of deer ked infestation on moose foraging and metabolism at the level of infestation observed early in the infestation, but did not exclude an effect later in winter. Our findings suggested that moose generally tolerated moderate parasitism by keds. However, the increase in HCC at higher ked intensities suggested that the tolerance strategy could be disrupted with further increases in intensities and consequently may negatively affect animal health and welfare.

• Mysterud, Atle; Rivrud, Inger Maren; Gundersen, Vegard; Rolandsen, Christer Moe & Viljugrein, Hildegunn (2020). The unique spatial ecology of human hunters. Nature Human Behaviour. 4, s. 694–701. doi: 10.1038/s41562-020-0836-7. Fulltekst i vitenarkiv Vis sammendrag

  Human hunters are described as ‘superpredators’ with a unique ecology. Chronic wasting disease among cervids and African swine fever among wild boar are emerging wildlife diseases in Europe, with huge economic and cultural repercussions. Understanding hunter movements at broad scales has implications for how to control the spread of these diseases. Here we show, based on analysis of the settlement patterns and movements of hunters of reindeer (n = 9,685), red deer (n = 47,845), moose (n = 60,365) and roe deer (n = 42,530) from across Norway (2001–2017), that hunter density was more closely linked to human density than prey density and that hunters were largely migratory, aggregated with increasing regional prey densities and often used dogs. Hunter movements extended across Europe and to other continents. Our results provide extensive evidence that the broad-scale movements and residency patterns of postindustrial hunters relative to their prey differ from those of large carnivores.

• Johnsen, Julie Føske; Viljugrein, Hildegunn; Bøe, Knut Egil; Gulliksen, Stine Margrethe; Beaver, Annabelle & Grøndahl, Ann Margaret [Vis alle 8 forfattere av denne artikkelen] (2019). A cross-sectional study of suckling calves' passive immunity and associations with management routines to ensure colostrum intake on organic dairy farms. Acta Veterinaria Scandinavica (AVS). ISSN 0044-605X. 61. doi: 10.1186/s13028-019-0442-8. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Background: For suckling dairy calves, different management routines to ensure sufficient colostrum intake are applied: visual assessment, hand feeding supplemental colostrum or assistance. However, knowledge on the efficacy of these methods to prevent failure of passive transfer [FPT: serum immunoglobulin (IgG) < 10 g/L] is lacking. Our objectives were to explore FPT prevalence in suckling dairy calves and associations with common management routines to ensure colostrum intake. From 20 organic herds, 156 calf blood samples (mean ± SD; 7.8 ± 1.24 per herd) and 141 colostrum samples from the dams were analysed. All calves suckled the dam. Factors known to affect serum and colostrum IgG were evaluated, including the method applied by the producer to ensure calf colostrum intake and whether it deviated from routine practice for any reason. Results: The prevalence of FPT was 31%. Mean serum and colostrum IgG (± SD) were 16.0 ± 10.0 g/L and 39.4 ± 26.4 g/L, respectively. Only colostrum IgG was found to have a statistically significant influence on the prevalence of FPT. Variation in serum IgG was also explained mainly by colostrum IgG. Of calves receiving colostrum according to farm routine, calves receiving supplemental colostrum with a bottle had lower serum IgG levels than did calves receiving no additional colostrum. However, no within-herd effect was found. With a high between-herd variation, colostrum IgG ranged from 2 to 135 g/L, and only 23% of the samples had a IgG content > 50 g/L. Colostrum IgG was significantly higher in samples collected during spring, compared to samples collected during winter, and lower in 2nd parity cows. Conclusions: The results indicate that for calves capable of finding the udder and suckling independently, there is no direct benefit of routinely hand feeding colostrum although herd level factors (e.g. feeding, management etc.) may play an important role. FPT prevalence in this study was high, and comparable to that of calves in conventional herds, separating cow and calf at birth. Still, the findings of a high FPT prevalence and inferior colostrum quality indicates a need for improved awareness among dairy producers practicing cow-calf suckling.

• Seljetun, Kristin Opdal; Eliassen, Elin; Madslien, Knut; Viljugrein, Hildegunn; Vindenes, Vigdis & Øiestad, Elisabeth Leere [Vis alle 7 forfattere av denne artikkelen] (2019). Prevalence of anticoagulant rodenticides in faeces of wild red foxes (Vulpes vulpes) in Norway. Journal of Wildlife Diseases. ISSN 0090-3558. 55(4), s. 834–843. doi: 10.7589/2019-01-027. Fulltekst i vitenarkiv Vis sammendrag

  High occurrence of anticoagulant rodenticides (ARs) in wildlife is a rising concern, with numerous reports of secondary exposure through predation. Because of widespread distribution of the red fox (Vulpes vulpes), they may act as sentinels for small mammal-hunting predators in rural, suburban, and urban areas. No AR surveillance in wild mammals with analyses of residues in feces has been conducted throughout a single country. We collected 163 fecal samples from presumed healthy red foxes from 18 out of 19 counties in Norway. The foxes were shot during regular hunting between January and December 2016 and samples collected directly after death. Fecal samples were analyzed for six ARs: brodifacoum, bromadiolone, coumatetralyl, difenacoum, difethialone, and flocoumafen. We detected ARs in 54% (75/139) of the animals. Brodifacoum was most frequently detected (46%; 64/139), followed by coumatetralyl (17%; 23/139), bromadiolone (16%; 22/139), difenacoum (5%; 7/139), difethialone (1%; 2/139), and flocoumafen (1%; 2/139). More than one substance was detected in 40% (30/75) of the positive foxes, and 7% (5/75) of these animals were exposed to four different ARs. There were no statistically significant seasonal, age, or sex differences in foxes after exposure to one AR compound. We found a significant difference in occurrence of brodifacoum and coumatetralyl in foxes from different geographical areas. These findings demonstrate fecal analyses as a valuable method of detecting AR exposure in red foxes. We suggest using direct fecal sampling with analyses as a method to evaluate the occurrence of ARs in live endangered wildlife in connection with radio tagging or collaring operations.

• Handeland, Kjell; Davidson, Rebecca K.; Viljugrein, Hildegunn; Mossing, Anders; Meisingset, Erling L. & Heum, Marianne [Vis alle 8 forfattere av denne artikkelen] (2019). Elaphostrongylus and Dictyocaulus infections in Norwegian wild reindeer and red deer populations in relation to summer pasture altitude and climate. International Journal for Parasitology: Parasites and Wildlife. 10, s. 188–195. doi: 10.1016/j.ijppaw.2019.09.003. Fulltekst i vitenarkiv Vis sammendrag

  Nematodes of the genera Elaphostrongylus and Dictyocaulus are associated with disease in semi-domesticated tundra reindeer and farmed red deer whereas less knowledge exists in the wild. Their first stage larvae (L1) develop to the infective third stage (L3) in the environment; Elaphostrongylus spp. within intermediate gastropod hosts and Dictyocaulus spp. as free-living larvae. Larval development of Elaphostrongylus is highly temperature dependent with a developmental minimum of 9–10 °C. Larval development of Dictyocaulus spp. may occur at low temperatures (5 °C) but the larvae are sensitive to desiccation. We examined the prevalence and intensity of Elaphostrongylus spp. and Dictyocaulus spp. infections in six wild reindeer and two wild red deer populations in relation to altitude, temperature and rainfall in their respective main summer pasture area over the 5 summers prior to sampling. The parasitological examination was based upon morphological identification of L1 in the faeces of hunted animals. Altitude was calculated from animal position data and temperature and precipitation by means of a nationwide gridded data set. Temperature decreased with increasing altitude, from 13.3 °C for the lowest located red deer population (300 m) to 6.1 °C for the highest located reindeer population (1400 m). No significant relationship between altitude and rainfall was identified. Elaphostrongylus spp. infection decreased in prevalence with increasing altitude, being identified in 89% of investigated samples from the lowest located population and in 3% of samples from the highest. The prevalence of Dictyocaulus spp. infection varied between 28 and 80% and no relationship with altitude was found. The intensity of Elaphostrongylus spp. infection was low in reindeer and moderate in red deer whereas the intensity of Dictyocaulus spp. infection was moderate in both species. Our results indicated that the climatic conditions in all areas studied were suitable for Dictyocaulus spp., whereas summer temperature was a restrictive factor for Elaphostrongylus sp. in reindeer.

• Mysterud, Atle; Madslien, Knut Ivar Engesæter; Viljugrein, Hildegunn; Vikøren, Turid; Andersen, Roy & Calderon, Mariella Evelyn Guere [Vis alle 13 forfattere av denne artikkelen] (2019). The demographic pattern of infection with chronic wasting disease in reindeer at an early epidemic stage. Ecosphere. 10(11), s. 1–11. doi: 10.1002/ecs2.2931. Fulltekst i vitenarkiv Vis sammendrag

  Infection patterns linked to age and sex are crucial to predict the population dynamic effects of diseases in long-lived species. How such demographic patterns of infection arise is often multifactorial, although the cause is commonly seen as a combination of immune status as well as variation in pathogen exposure. Prion diseases are particularly interesting, as they do not trigger an adaptive immune response; hence, differences in pathogen exposure linked to behavior could be the prime determinant of the pattern of infection. In cervids, the fatal prion disease, chronic wasting disease (CWD), is spreading geographically, with economic and cultural consequences in affected areas in North America, and all infected individuals eventually die from disease-associated sequelae if they live long enough. Understanding the causes of the demographic pattern of infection with CWD is therefore urgent but is limited by the fact that reported data primarily come from related deer species in North America. The recent (detected 2016) emergence of CWD among wild alpine reindeer (Rangifer tarandus) in Norway with a different social organization, that is, no home range behavior and no matrilineal female groups, offers an opportunity to advance our understanding of how behavior influences the infection patterns. Testing of 1081 males and 1278 females detected 19 animals positive for abnormal prion protein in brain and/or lymphatic tissues. No calves and only one male yearling were infected, with the remaining positives being adults (representing 1.5% of adult males and 0.5% of adult females). We found a strong sex-biased infection pattern in reindeer (with infection 2.7 times more likely in adult males), which is similar to the results reported in mule deer and white-tailed deer. The hazard of being detected as positive increased with age in males. There was no close genetic relatedness among positive animals. The results were consistent with the within-group contact of males being a possible major route of transmission. We discuss the demographic pattern of infection with CWD in view of the lack of stable home range behavior and other key behavioral traits of reindeer relevant to understanding pathogen exposure in general. irect contact; disease ecology; environmental reservoirs; pathogen exposure; population dynamics; prions; social organization; transmission.

• Mysterud, Atle; Heylen, Dieter J. A.; Matthysen, Erik; Garcia, Aïda Lopez; Jore, Solveig & Viljugrein, Hildegunn (2019). Lyme neuroborreliosis and bird populations in northern Europe. Proceedings of the Royal Society of London. Biological Sciences. ISSN 0962-8452. 286(1903), s. 1–10. doi: 10.1098/rspb.2019.0759. Fulltekst i vitenarkiv Vis sammendrag

  Many vector-borne diseases are transmitted through complex pathogen–vector–host networks, which makes it challenging to identify the role of specific host groups in disease emergence. Lyme borreliosis in humans is now the most common vector-borne zoonosis in the Northern Hemisphere. The disease is caused by multiple genospecies of Borrelia burgdorferi sensulato bacteria transmitted by ixodid (hard) ticks, and the major host groups transmit Borrelia genospecies with different pathogenicity, causing variable clinical symptoms in humans. The health impact of a given host group is a function of the number of ticks it infects as well as the pathogenicity of the genospecies it carries. Borrelia afzelii, with mainly small mammals as reservoirs, is the most common pathogen causing Lyme borreliosis, and it is often responsible for the largest proportion of infected host-seeking tick nymphs in Europe. The bird-borne Borrelia garinii, though less prevalent in nymphal ticks, is more likely to cause Lyme neuroborreliosis, but whether B. garinii causes disseminated disease more frequently has not been documented. Based on extensive data of annual disease incidence across Norway from 1995 to 2017, we show here that 69% of disseminated Lyme borreliosis cases were neuroborreliosis, which is three times higher than predicted from the infection prevalence of B. garinii in host-seeking ticks (21%). The population estimate of migratory birds, mainly of thrushes, explained part of the annual variation in cases of neuroborreliosis, with a one-year time lag. We highlight the important role of the genospecies' pathogenicity and the host associations for understanding the epidemiology of disseminated Lyme borreliosis.

• Mysterud, Atle; Stigum, Vetle Malmer; Linløkken, Harald Kolstad; Herland, Anders & Viljugrein, Hildegunn (2019). How general are generalist parasites? The small mammal part of the Lyme disease transmission cycle in two ecosystems in northern Europe. Oecologia. ISSN 0029-8549. 190(1), s. 115–126. doi: 10.1007/s00442-019-04411-2. Fulltekst i vitenarkiv Vis sammendrag

  The pathogens causing Lyme disease are all vectored by generalist tick species found on a wide range of vertebrates, but spatial and annual variation in host use has rarely been quantified. We here compare the load of Ixodes ricinus (the vector) on small mammals and investigate the infection prevalence of Borrelia burgdorferi s.l. (the pathogen) involved in the enzootic transmission cycle of Lyme disease in two contrasting ecosystems in Norway from 2014 to 2016. The most common larval tick host in the eastern region was the bank vole, while the common shrew dominated in the western region of Norway. However, the wood mouse and the bank vole had consistently higher larval tick loads than the common shrew in both ecosystems. Hence, the evidence indicated that species are differently suitable as hosts, regardless of their abundances. The pathogen infection prevalence was similar among small mammal species, but markedly higher in the region with larger small mammal populations and higher tick loads, while the seasonal and annual variation was less marked. Our study indicated that the generalist I. ricinus shows consistent patterns of load on species of small vertebrate hosts, while B. burgdorferi s.l. (B. afzelii) was a true generalist. The similar roles of host species across regions suggest that disease dynamics can be predicted from host community composition, but predicting the role of host community composition for disease dynamics requires a detailed understanding of the different species population limitations under global change.

• Mysterud, Atle; Viljugrein, Hildegunn; Solberg, Erling Johan & Rolandsen, Christer Moe (2019). Legal regulation of supplementary cervid feeding facing chronic wasting disease. Journal of Wildlife Management. ISSN 0022-541X. 83(8), s. 1667–1675. doi: 10.1002/jwmg.21746. Fulltekst i vitenarkiv Vis sammendrag

  The supplementary feeding of cervids is a widespread practice across the northern hemisphere. There are few studies, however, regarding the extent of feeding in space and time. There are adverse effects of supplementary feeding, of which the most severe are increased parasite and disease transmission. With the recent emergence of chronic wasting disease (CWD) among cervids in Norway, a legal regulation was issued that banned all supplementary cervid feeding. We quantified the spatial extent and intentions of feeding cervids across all of Norway using a questionnaire at the municipality scale. We also compared spatial extent of feeding before and after the feeding ban to shed light on the ability of regulations to control supplementary feeding. Supplementary feeding to increase winter survival and targeting roe deer (Capreolus capreolus) was more common (48.4% of the municipalities) than the feeding of red deer (Cervus elaphus; 20.5%) and moose (Alces alces; 7.4%). The main feeding period was January–March, but extensive feeding also occurred from November to December and in April. Reducing traffic accidents was also a motivation, particularly for the feeding of moose (14.5%), and this was the main motivation (86%) for public feeding. Among the 65.7% that responded, 53.3% reported they knew about supplemental feeding of cervids in their municipality. In the region with the first feeding ban, 80.2% of municipalities were feeding in 2015–2016 before the ban, which was reduced to 68.4% in 2016–2017 and remained at 68.4% in 2017–2018. In the remainder of Norway, 81.4% were feeding in 2015–2016, and 72.6% were feeding in 2016–2017, but after the ban, this increased to 78.6% in the harsh winter of 2017–2018. Our study highlights that regulations across broad scales may not be followed and that more spatially targeted regulations and increased enforcement are required for disease transmission to be more effectively combated. © 2019 The Authors. Journal of Wildlife Management published by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

• Mysterud, Atle; Stigum, Vetle Malmer; Seland, Ingrid Vikingsdal; Herland, Anders; Easterday, William Ryan & Jore, Solveig [Vis alle 8 forfattere av denne artikkelen] (2018). Tick abundance, pathogen prevalence, and disease incidence in two contrasting regions at the northern distribution range of Europe. Parasites & Vectors. 11(309). doi: 10.1186/s13071-018-2890-9. Fulltekst i vitenarkiv Vis sammendrag

  Background Emergence of tick-borne diseases is impacting humans and livestock across the Northern Hemisphere. There are, however, large regional variations in number of cases of tick-borne diseases. Some areas have surprisingly few cases of disease compared to other regions. The aim here is to provide a first step towards a better understanding of such contrasting regional patterns of disease emergences at the northern distribution range of Ixodes ricinus in Europe. Methods We compare disease incidence, vector abundance and pathogen prevalence in eastern and western Norway differing in the number of tick-borne disease cases. First, we analysed the incidence of Lyme borreliosis in humans, tick-borne fever (anaplasmosis) in sheep and anaplasmosis and babesiosis in cattle to verify if incidence differed. Secondly, we analysed extensive field data on questing tick density, pathogen prevalence, as well as the broad spatial pattern of human and livestock distribution as it may relate to tick exposure. Results The incidences of all diseases were lower in eastern, compared to western, Norway, but this was most marked for the livestock diseases. While the prevalence of Borrelia burgdorferi (sensu lato) in ticks was similar in the two regions, the prevalence of Anaplasma phagocytophilum was markedly lower in eastern, compared to western, Norway. We found overall a lower abundance of questing nymphs in the east. In the east, there were cases of babesiosis in cattle where anaplasmosis was absent, suggesting absence of the pathogen rather than differences in exposure to ticks as part of the explanation for the much lower incidence of anaplasmosis in eastern Norway. Conclusions Many factors contribute to different disease incidence across ecosystems. We found that regional variation in tick-borne disease incidence may be partly linked to vector abundance and pathogen prevalence, but differently for human and livestock diseases. Further studies are needed to determine if there is also regional variation in specific genospecies and strain frequencies differing in pathogenicity.

• Viljugrein, Hildegunn; Hopp, Petter; Benestad, Sylvie Lafond; Nilsen, Erlend Birkeland; Våge, Jørn & Tavornpanich, Saraya [Vis alle 9 forfattere av denne artikkelen] (2018). A method that accounts for differential detectability in mixed samples of long-term infections with applications to the case of Chronic Wasting Disease in cervids. Methods in Ecology and Evolution. s. 1–12. doi: 10.1111/2041-210X.13088. Fulltekst i vitenarkiv Vis sammendrag

  1. Surveillance of wildlife diseases is logistically difficult, and imperfect detection is a recurrent challenge for disease estimation. Using citizen science can increase sample sizes, but it is associated with a cost in terms of the anatomical type and quality of the sample. Additionally, biological tissue samples from remote areas lose quality due to autolysis. These challenges are faced in the case of emerging Chronic Wasting Disease (CWD) in cervids. 2. Here, we develop a stochastic scenario tree model of diagnostic sensitivity, allowing for a mixture of tissue sample types (lymph nodes and brain) and qualities while accounting for different detection probabilities during the CWD infection, lasting 2-3 years. We apply the diagnostic sensitivity in a Bayesian framework, enabling estimation of age-class-specific true prevalence, including the prevalence in latent, recently infected stages. We provide a simulation framework to estimate the sensitivity of the surveillance system (i.e., the probability of detecting the infection in a given population), when detectability varies among individuals due to different disease progression. 3. We demonstrate the utility of our framework by applying it to the recent emergence of CWD in a European population of reindeer. We estimated apparent CWD prevalence at 1.2 % of adults in the infected population of wild reindeer, while the true prevalence was 1.6 %. The sensitivity estimation of the CWD surveillance was performed in an adjacent small (~500) and a large (~10,000) reindeer population, demonstrating low certainty of CWD absence. 4. Our method has immediate application to the mandatory testing for CWD in EU countries commencing in 2018. Similar approaches that account for latent stages and a serial disease progression in various tissues with a temporal pattern of diagnostic sensitivity may enhance the estimation of the prevalence of wildlife diseases more generally. Bayesian estimation methods, surveillance, wildlife diseases, diagnostic sensitivity, test sensitivity, chronic wasting disease, prevalence, prions, PrP CWD

• Kristoffersen, Anja Bråthen; Qviller, Lars; Helgesen, Kari Marie Olli; Vollset, Knut Wiik; Viljugrein, Hildegunn & Jansen, Peder A (2018). Quantitative risk assessment of salmon louse-induced mortality of seaward-migrating post-smolt Atlantic salmon. Epidemics. ISSN 1755-4365. 23, s. 19–33. doi: 10.1016/j.epidem.2017.11.001. Fulltekst i vitenarkiv
• Flem, Belinda; Moen, Vidar; Finne, Tor Erik; Viljugrein, Hildegunn & Kristoffersen, Anja Bråthen (2017). Trace element composition of smolt scales from Atlantic salmon (Salmo salar L.), geographic variation between hatcheries. Fisheries Research. ISSN 0165-7836. 190, s. 183–196. doi: 10.1016/j.fishres.2017.02.010. Fulltekst i vitenarkiv
• Aldrin, Magne Tommy; Huseby, Ragnar Bang; Stien, Audun; Grøntvedt, Randi Nygaard; Viljugrein, Hildegunn & Jansen, Peder A (2017). A stage-structured Bayesian hierarchical model for salmon lice populations at individual salmon farms – Estimated from multiple farm data sets. Ecological Modelling. ISSN 0304-3800. 359, s. 333–348. doi: 10.1016/j.ecolmodel.2017.05.019. Fulltekst i vitenarkiv Vis sammendrag

  Salmon farming has become a prosperous international industry over the last decades. Along with growth in the production farmed salmon, however, an increasing threat by pathogens has emerged. Of special concern is the propagation and spread of the salmon louse, Lepeophtheirus salmonis. To gain insight into this parasite’s population dynamics in large scale salmon farming system, we present a fully mechanistic stage-structured population model for the salmon louse, also allowing for complexities involved in the hierarchical structure of full scale salmon farming. The model estimates parameters controlling a wide range of processes, including temperature dependent demographic rates, fish size and abundance effects on louse transmission rates, effect sizes of various salmon louse control measures, and distance based between farm transmission rates. Model parameters were estimated from data including 32 salmon farms, except the last production months for five farms, which were used to evaluate model predictions. We used a Bayesian estimation approach, combining the prior distributions and the data likelihood into a joint posterior distribution for all model parameters. The model generated expected values that fitted the observed infection levels of the chalimus, adult female and other mobile stages of salmon lice, reasonably well. Predictions for the periods not used for fitting the model were also consistent with the observational data. We argue that the present model for the population dynamics of the salmon louse in aquaculture farm systems may contribute to resolve the complexity of processes that drive this host-parasite relationship, and hence may improve strategies to control the parasite in this production system. Population model Aquaculture Stochastic model Sea lice counts

• Handeland, Kjell; Viljugrein, Hildegunn; Lierhagen, Syverin; Opland, Marthe; Tarpai, Attila & Vikøren, Turid (2017). Low copper levels associated with low carcass weight in wild red deer (Cervus elaphus) in Norway. Journal of Wildlife Diseases. ISSN 0090-3558. 53(1), s. 176–180. doi: 10.7589/2016-02-037. Fulltekst i vitenarkiv
• Mysterud, Atle; Jore, Solveig; Østerås, Olav & Viljugrein, Hildegunn (2017). Emergence of tick-borne diseases at northern latitudes in Europe: a comparative approach. Scientific Reports. 7. doi: 10.1038/s41598-017-15742-6. Fulltekst i vitenarkiv Vis sammendrag

  The factors that drive the emergence of vector-borne diseases are difficult to identify due to the complexity of the pathogen-vector-host triad. We used a novel comparative approach to analyse four long-term datasets (1995–2015) on the incidence of tick-borne diseases in humans and livestock (Lyme disease, anaplasmosis and babesiosis) over a geographic area that covered the whole of Norway. This approach allowed us to separate general (shared vector) and specific (pathogen reservoir host) limiting factors of tick-borne diseases, as well as the role of exposure (shared and non-shared pathogens in different hosts). We found broadly similar patterns of emergence across the four tick-borne diseases. Following initial increases during the first decade of the time series, the numbers of cases peaked at slightly different years and then stabilized or declined in the most recent years. Contrasting spatial patterns of disease incidence were consistent with exposure to ticks being an important factor influencing disease incidence in livestock. Uncertainty regarding the reservoir host(s) of the pathogens causing anaplasmosis and babesiosis prevented a firm conclusion regarding the role of the reservoir host-pathogen distribution. Our study shows that the emergence of tick-borne diseases at northern latitudes is linked to the shared tick vector and that variation in host-pathogen distribution and exposure causes considerable variation in emergence.

• Mysterud, Atle; Easterday, William Ryan; Stigum, Vetle Malmer; Aas, Anders Bjørnsgard; Meisingset, Erling L. & Viljugrein, Hildegunn (2016). Contrasting emergence of Lyme disease across ecosystems. Nature Communications. 7. doi: 10.1038/ncomms11882. Fulltekst i vitenarkiv Vis sammendrag

  Global environmental changes are causing Lyme disease to emerge in Europe. The life cycle of Ixodes ricinus, the tick vector of Lyme disease, involves an ontogenetic niche shift, from the larval and nymphal stages utilizing a wide range of hosts, picking up the pathogens causing Lyme disease from small vertebrates, to the adult stage depending on larger (non-transmission) hosts, typically deer. Because of this complexity the role of different host species for emergence of Lyme disease remains controversial. Here, by analysing long-term data on incidence in humans over a broad geographical scale in Norway, we show that both high spatial and temporal deer population density increase Lyme disease incidence. However, the trajectories of deer population sizes play an overall limited role for the recent emergence of the disease. Our study suggests that managing deer populations will have some effect on disease incidence, but that Lyme disease may nevertheless increase as multiple drivers are involved.

• Mysterud, Atle; Madslien, Knut; Herland, Anders; Viljugrein, Hildegunn & Ytrehus, Bjørnar (2016). Phenology of deer ked (Lipoptena cervi) host-seeking flight activity and its relationship with prevailing autumn weather. Parasites & Vectors. 9(95), s. 1–6. doi: 10.1186/s13071-016-1387-7. Fulltekst i vitenarkiv Vis sammendrag

  Background: The deer ked (Lipoptena cervi) is an ectoparasite on cervids that has invaded large parts of Norway, Sweden and Finland during recent decades. During their host-seeking flight activity, the adult deer keds constitute a considerable nuisance to people and limit human outdoor recreation. The bites of the deer ked can cause long-lasting dermatitis in humans. Determining the pattern of flight activity during autumn is hence important. Methods: Data on flight phenology was gathered by walking along transects in the forest in two counties of Norway during 2009–2013, counting the number of host-seeking keds. We analysed how the flight activity of deer keds varied depending on date and prevailing weather during autumn. Results: The best model of flight activity included both date and temperature, both as nonlinear terms. Host-seeking deer keds were observed from early August to mid-November with a marked peak in late September. Number of host-seeking keds declined with temperatures falling below the mean, but did not increase much at above mean temperatures. The pattern of flight phenology was similar across the two counties and five years. Conclusions: Parasitic arthropods may be strongly affected by prevailing weather during off-host periods. Our study shows an estimated positive effect of temperature on deer ked flight activity mainly for below mean temperatures in late autumn, while the effect of temperature on flight activity in early autumn was weak. The pattern of host-seeking flight activity during late, rather than early autumn, is hence more likely to change with ongoing climate change, with a predicted increase in duration of the host-seeking period. Keywords: Deer ked, Invading parasites, Climate, Temperature, Moose, Phenology

• Stene, Anne; Hellebø, Audny; Viljugrein, Hildegunn; Solevåg, Stein Eric; Devold, Magnus & Aspehaug, Vidar (2016). Liquid fat, a potential abiotic vector for horizontal transmission of salmonid alphavirus? Journal of Fish Diseases. ISSN 0140-7775. 39(5), s. 531–537. doi: 10.1111/jfd.12382. Fulltekst i vitenarkiv Vis sammendrag

  Viral diseases represent serious Challenge in marine farming of Atlantic salmon (Salmo salar L.) Pancreas disease (PD) caused by a salmonid alphavirus (SAV) is by far the most serious in Northern Europe. To Control PD, it is necessary to identify virus transmission routes. One aspect to consider is whether the virus is transported as free particles or Associated With potential vectors. Farmed salmonids have high lipid content in their tissue which may be released into the environment from decomposing dead Fish. At the seawater surface, the effects of Wind and Ocean currents are most prominent. The aim of this study was primarily to identify whether the lipid fraction leaking from dead infected salmon contains SAV. Adipose tissue from dead SAV-infected Fish from Three farming sites was submerged in beakers With sea water in the Laboratory and stored at different tempewrature and time conditions. SAV was identified by real-time RT-PCR in the lipid fractions accumulating at the water surface in the beakers. SAV-RNA was also present in the sea water. lipid fractions were transferred to cell culture, and viable SAV was identified. Due to its hydrophobic nature, fat With inefective pathogenic virus at the surface may contribute to long-distance transmission of SAV.

• Lyngstad, Trude Marie; Hellberg, Hege; Viljugrein, Hildegunn; Jensen, Britt Bang; Brun, Edgar & Sergeant, Evan [Vis alle 7 forfattere av denne artikkelen] (2016). Routine clinical inspections in Norwegian marine salmonid sites: A key role in surveillance for freedom from pathogenic viral haemorrhagic septicaemia (VHS). Preventive Veterinary Medicine. ISSN 0167-5877. 124, s. 85–95. doi: 10.1016/j.prevetmed.2015.12.008. Fulltekst i vitenarkiv
• Qviller, Lars; Viljugrein, Hildegunn; Loe, Leif Egil; Meisingset, Erling L. & Mysterud, Atle (2016). The influence of red deer space use on the distribution of Ixodes ricinus ticks in the landscape. Parasites & Vectors. 9(1). doi: 10.1186/s13071-016-1825-6. Fulltekst i vitenarkiv Vis sammendrag

  Background: Many wingless ectoparasites have a limited capacity for active movement and are therefore primarily dependent on hitchhiking on their hosts for transportation. The distribution of the tick Ixodes ricinus is expected to depend mainly on transportation by hosts and tick subsequent survival in areas where they drop off. In Europe, the most important hosts of adult female I. ricinus are cervids. The extensive space use of large hosts provides a much larger dispersal potential for I. ricinus than that of smaller mammalian hosts. We aim to determine the contribution of red deer (Cervus elaphus) space use on the spatial distribution of I. ricinus, after accounting for landscape factors. Methods: We analysed the spatial distribution of I. ricinus with generalised mixed effects models (GLMMs) based on data from extensive field surveys of questing density in two coastal regions in Norway, from which home range data from 73 red deer with GPS collars were available. Red deer home ranges were derived using the kernel method to identify areas most frequently used by deer. We first fitted a baseline model with tick questing densities relative to landscape features that are likely to affect local climate conditions and hence, survival. We then added deer space use variables to the baseline model with only landscape variables to test whether areas more frequently used by red deer had higher questing tick densities. Results: Questing I. ricinus density was predicted by several landscape features, such as elevation, distance to the fjord and topographic slope. In addition, we found that areas more heavily used within the red deer home ranges, correlated with higher questing tick densities. Increased effects of deer space use were additive to the landscape model, suggesting that correlations were more than just shared landscape preferences between deer and ticks. Conclusions: Our results imply that the distribution of I. ricinus is controlled by a complex set of factors that include both local conditions related to landscape properties that affect survival and how the large host population redistributes ticks. In particular, we have provided evidence that the local distribution of large hosts, with their extensive space use, redistributes ticks at the local scale.

• Heier, Lise; Viljugrein, Hildegunn & Storvik, Geir Olve (2015). Persistence of plague outbreaks among great gerbils in Kazakhstan: effects of host population dynamics. Population Ecology. ISSN 1438-3896. 57(3), s. 473–484. doi: 10.1007/s10144-015-0500-7. Fulltekst i vitenarkiv
• Mysterud, Atle; Qviller, Lars; Meisingset, Erling L. & Viljugrein, Hildegunn (2015). Parasite load and seasonal migration in red deer. Oecologia. ISSN 0029-8549. 108(2), s. 401–407. doi: 10.1007/s00442-015-3465-5. Fulltekst i vitenarkiv
• Mysterud, Atle; Byrkjeland, Ragna; Qviller, Lars & Viljugrein, Hildegunn (2015). The generalist tick Ixodes ricinus and the specialist tick Ixodes trianguliceps on shrews and rodents in a northern forest ecosystem – a role of body size even among small hosts. Parasites & Vectors. 8(639). doi: 10.1186/s13071-015-1258-7. Fulltekst i vitenarkiv Vis sammendrag

  Background Understanding aggregation of ticks on hosts and attachment of life stages to different host species, are central components for understanding tick-borne disease epidemiology. The generalist tick, Ixodes ricinus, is a well-known vector of Lyme borrelioses, while the specialist tick, Ixodes trianguliceps, feeding only on small mammals, may play a role in maintaining infection levels in hosts. In a northern forest in Norway, we aimed to quantify the role of different small mammal species in feeding ticks, to determine the extent to which body mass, even among small mammals, plays a role for tick load, and to determine the seasonal pattern of the two tick species. Methods Small mammals were captured along transects in two nearby areas along the west coast of Norway. All life stages of ticks were counted. Tick load, including both prevalence and intensity, was analysed with negative binomial models. Results A total of 359 rodents and shrews were captured with a total of 1106 I. ricinus (60.0 %) and 737 I. trianguliceps (40.4 %), consisting of 98.2 % larvae and 1.8 % nymphs of I. ricinus and 91.2 % larvae, 8.7 % nymphs and 0.1 % adult females of I. trianguliceps. Due to high abundance, Sorex araneus fed most of the larvae of both tick species (I. ricinus 61.9 %, I. trianguliceps 64.9 %) with Apodemus sylvaticus (I. ricinus 20.4 %, I. trianguliceps 10.0 %) and Myodes glareolus (I. ricinus 10.9 %, I. trianguliceps 9.5 %) as the next most important hosts. Individual A. sylvaticus and M. glareolus had higher infestation intensity than S. araneus, while Sorex minutus had markedly lower infestation intensity. The load of I. ricinus larvae and nymphs was related to body mass mainly up to ~10 g, while the load of I. trianguliceps was less dependent of body mass. The load of I. trianguliceps was higher in spring than in fall, while the seasonal pattern was reversed for I. ricinus with higher loads in fall. Conclusions Body mass was important for explaining load of I. ricinus mainly up to a body mass of ~10 g across a range of smaller mammalian hosts. Consistent with earlier work elsewhere in Europe, we found the highest tick infestation intensity on the wood mouse A. sylvaticus. However, this rodent species fed only 20.4 % of all I. ricinus larvae, while the much more abundant S. araneus fed 61.9 %. Our study emphasizes an important quantitative role of the common shrew S. araneus as a main host to I. ricinus larvae and to both I. trianguliceps larvae and nymphs. The partly seasonal distinct attachment pattern of I. ricinus and I. trianguliceps is evidence for niche separation.

• Kristoffersen, Anja Bråthen; Jimenez, Daniel Delgado; Viljugrein, Hildegunn; Grøntvedt, Randi; Stien, Audun & Jansen, Peder A (2014). Large scale modelling of salmon lice (Lepeophtheirus salmonis) infection pressure based on lice monitoring data from Norwegian salmonid farms. Epidemics. ISSN 1755-4365. 9, s. 31–39. doi: 10.1016/j.epidem.2014.09.007. Fulltekst i vitenarkiv Vis sammendrag

  Infection by parasitic sea lice is a substantial problem in industrial scale salmon farming. To controlthe problem, Norwegian salmonid farms are not permitted to exceed a threshold level of infection ontheir fish, and farms are required to monitor and report lice levels on a weekly basis to ensure compliancewith the regulation. In the present study, we combine the monitoring data with a deterministic model forsalmon lice population dynamics to estimate farm production of infectious lice stages. Furthermore, weuse an empirical estimate of the relative risk of salmon lice transmission between farms, that depend oninter-farm distances, to estimate the external infection pressure at a farm site, i.e. the infection pressurefrom infective salmon lice of neighbouring farm origin. Finally, we test whether our estimates of infectionpressure from neighbouring farms as well as internal within farm infection pressure, predicts subsequentdevelopment of infection in cohorts of farmed salmonids in their initial phase of marine production. Wefind that estimated external infection pressure is a main predictor of salmon lice population dynamicsin newly stocked cohorts of salmonids. Our results emphasize the importance of keeping the productionof infectious lice stages at low levels within local networks of salmon farms. Our model can easily beimplemented for real time estimation of infection pressure at the national scale, utilizing the masses ofdata generated through the compulsory lice monitoring in salmon farms. The implementation of such asystem should give the salmon industry greater predictability with respect to salmon lice infection levels,and aid the decision making process when the development of new farm sites are planned.© 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-NDlicense (http://creativecommons.org/licenses/by-nc-nd/3.0/). Parasites, Spatial models, Infective stages, Density effects, Aquaculture

Se alle arbeider i NVA

• Osnes, Magnus Nygård; Viljugrein, Hildegunn; Dean, Katharine Rose & Wolff, Cecilia Mia (2026). Estimating the relative risk of HPAI presence in wild birds and spillover to commercial poultry farms in Norway: a spatiotemporal risk-mapping approach. Fulltekst i vitenarkiv Vis sammendrag

  Highly pathogenic avian influenza (HPAI) poses an increasing threat to commercial poultry production across Europe. In Norway, six outbreaks in commercial flocks have been recorded since 2021, most in the poultry-dense region of Rogaland county. Despite increased surveillance activities, Norway currently lacks quantitative spatial estimates of HPAI introduction risk to commercial poultry. This study aims to produce a high-resolution, season-specific relative risk map of HPAI presence in wild birds and subsequent spillover risk to commercial poultry farms in Norway. Risk factors were identified through a scoping literature review and assessed for relevance to the Norwegian context in consultation with specialist veterinarians and international collaborators. Risk factor weights were derived using the Best-Worst Method (BWM), a structured expert elicitation approach that enables efficient and consistent pairwise comparisons. Spatial risk layers were constructed at 5x5 km resolution across mainland Norway, including composite seasonal abundance of wild waterfowl and seabirds (based on citizen science data), CORINE land cover classes, human population density, poultry farm and bird density, and historical HPAI detection data. Layers were combined as a weighted mean, producing risk maps for winter, spring, summer, and autumn. Sensitivity to weight uncertainty was assessed through a weight-perturbation approach, and maps were validated against historical HPAI confirmations in wild birds and the locations of the commercial farm outbreaks. The seasonal framework captures the shifting distribution of reservoir host species across Norway's broad latitudinal range. The resulting maps provide a decision-support tool for targeted surveillance prioritisation and biosecurity interventions, and demonstrate how expert-weighted spatial models can be applied in data-limited settings where outbreak frequency is insufficient for purely statistical approaches.

• Osnes, Magnus Nygård; Mysterud, Atle; Dean, Katharine Rose; Tranulis, Michael A.; Widgren, Stefan & Viljugrein, Hildegunn (2025). Modeling the effects of PRNP genotype linked to susceptibility, disease duration and prion shedding on chronic wasting disease dynamics of cervids. Fulltekst i vitenarkiv
• Osnes, Magnus Nygård; Mysterud, Atle; Dean, Katharine Rose; Tranulis, Michael A.; Widgren, Stefan & Viljugrein, Hildegunn (2025). Modeling the effects of PRNP genotype on chronic wasting disease dynamics of cervids. Fulltekst i vitenarkiv
• Osnes, Magnus Nygård; Mysterud, Atle; Widgren, Stefan; Dean, Katharine Rose; Tranulis, Michael A. & Viljugrein, Hildegunn (2025). Modelling the effect of genotype (PRNP) linked to susceptibility, duration and level of prion shedding on chronic wasting disease dynamics of cervids. Fulltekst i vitenarkiv
• Viljugrein, Hildegunn (2024). CWD in Norway and initial work on a CWD spread model. Fulltekst i vitenarkiv
• Dean, Katharine Rose; Hopp, Petter; Grøntvedt, Carl Andreas & Viljugrein, Hildegunn (2024). Description of the pig population and live animal movements in Norway 2020-2022. Fulltekst i vitenarkiv
• Lindsø, Lars; Viljugrein, Hildegunn & Mysterud, Atle (2024). Correction to: Vector competence of Ixodes ricinus instars for the transmission of Borrelia burgdorferi sensu lato in different small mammalian hosts (Parasites & Vectors, (2024), 17, 1, (23), 10.1186/s13071-023-06110-7). Parasites & Vectors. 17(1). doi: 10.1186/s13071-024-06249-x. Fulltekst i vitenarkiv
• Rolandsen, Christer Moe; Moorter, Bram Van; Strand, Olav; Andersen, Roy; Solberg, Erling Johan & Viljugrein, Hildegunn [Vis alle 7 forfattere av denne artikkelen] (2023). Bi-effekter av cwd-tiltak? Bukkeandel, alder, genetikk, skjeve kjønnsrater, kalvevekter, kalveproduksjon, dødelighet, forstyrrelser/arealbruk. Fulltekst i vitenarkiv
• Fosse, Johanna Hol; Aamelfot, Maria; Andresen, Adriana Magalhaes Santos; Ploss, Frieda Betty; Weli, Simon Chioma & Solhaug, Anita [Vis alle 14 forfattere av denne artikkelen] (2023). The infectious salmon anaemia virus sialic acid 4-O-acetyl esterase extensively prunes target cell surfaces in infected hosts. Fulltekst i vitenarkiv
• Koutsoumanis, K.; Allende, A.; Alvarez-Ordonez, A.; Bolton, D.; Bover-Cid, S. & Chemaly, M. [Vis alle 24 forfattere av denne artikkelen] (2023). Monitoring of chronic wasting disease (CWD) (IV). EFSA Journal. ISSN 1831-4732. 21, s. 1–103. doi: 10.2903/j.efsa.2023.7936. Fulltekst i vitenarkiv Vis sammendrag

  The European Commission requested an analysis of the Chronic Wasting Disease (CWD) monitoring programme in Norway, Sweden, Finland, Iceland, Estonia, Latvia, Lithuania and Poland (9 January 2017–28 February 2022). Thirteen cases were detected in reindeer, 15 in moose and 3 in red deer. They showed two phenotypes, distinguished by the presence or absence of detectable disease-associated normal cellular prion protein (PrP) in lymphoreticular tissues. CWD was detected for the first time in Finland, Sweden and in other areas of Norway. In countries where the disease was not detected, the evidence was insufficient to rule out its presence altogether. Where cases were detected, the prevalence was below 1%. The data also suggest that the high-risk target groups for surveillance should be revised, and ‘road kill’ removed. Data show that, in addition to differences in age and sex, there are differences in the prion protein gene (PRNP) genotypes between positive and negative wild reindeer. A stepwise framework has been proposed with expanded minimum background surveillance to be implemented in European countries with relevant cervid species. Additional surveillance may include ad hoc surveys for four different objectives, specific to countries with/without cases, focusing on parallel testing of obex and lymph nodes from adult cervids in high-risk target groups, sustained over time, using sampling units and a data-driven design prevalence. Criteria for assessing the probability of CWD presence have been outlined, based on the definition of the geographical area, an annual assessment of risk of introduction, sustained minimum background surveillance, training and engagement of stakeholders and a surveillance programme based on data-driven parameters. All positive cases should be genotyped. Sample sizes for negative samples have been proposed to detect and estimate the frequency of PRNP polymorphisms. Double-strand sequencing of the entire PRNP open reading frame should be undertaken for all selected samples, with data collated in a centralised collection system at EU level.

• Aamelfot, Maria; Fosse, Johanna Hol; Viljugrein, Hildegunn; Benestad, Sylvie L.; McBeath, Alastair & Christiansen, Debes Hammershaimb [Vis alle 8 forfattere av denne artikkelen] (2022). ILA-virusinfeksjon forandrer overflaten på laksens blodkar. Fulltekst i vitenarkiv
• Benestad, Sylvie Lafond; Tran, Linh; Hopp, Petter; Madslien, Knut; Moldal, Torfinn & Vikøren, Turid [Vis alle 9 forfattere av denne artikkelen] (2021). An update on CWD in Norway- scandinavian strains. Fulltekst i vitenarkiv
• Viljugrein, Hildegunn (2020). Flått fra sangfugl er farligst. Fulltekst i vitenarkiv
• Kristoffersen, Anja Bråthen; Qviller, Lars; Helgesen, Kari Marie Olli; Vollset, Knut Wiik; Viljugrein, Hildegunn & Jansen, Peder A (2019). Betydningen av lakselus for vill laksesmolt. Fulltekst i vitenarkiv
• Viljugrein, Hildegunn; Jore, Solveig & Mysterud, Atle (2018). Emergence of tick-borne diseases at Northern latitudes in Europe: a comparative approach. Fulltekst i vitenarkiv
• Neves, Carlos G Das; Våge, Jørn; Vikøren, Turid; Madslien, Knut; Hopp, Petter & Viljugrein, Hildegunn [Vis alle 7 forfattere av denne artikkelen] (2018). Battling CWD in Norway: an update on surveillance and disease development after 2 years on the map. Fulltekst i vitenarkiv Vis sammendrag

  Chronic Wasting Disease (CWD) is an invariably fatal neurodegenerative disease of cervids, belonging to the group of transmissible spongiform encephalopathies (TSE). The disease is endemic in some areas in North America, where natural infections occurs in different cervid species. Prior to 2016 CWD had never been reported outside North America except in captive deer in South Korea, introduced by import of CWD-infected animals. The surveillance for CWD in Europe has been limited, but for the period, 2018 - 2020 EU has launched a program in six member states. The program covers member states with moose (Alces alces) or reindeer (Rangifer tarandus tarandus). In Norway, approximately 2,100 cervids were tested for CWD in the period 2004-2015. Less than 20 of these were free-ranging reindeer (Rangifer tarandus tarandus). Norway is the last refugium for wild tundra reindeer in Europe. The species is found in fragmented sub-populations in remote alpine regions of South Norway. In March 2016, a young adult female reindeer belonging to the Nordfjella sub- population was found dying and was diagnosed as CWD positive. This case represented the first detection of CWD in Europe and the first detection of a natural infection in reindeer worldwide. Trough enhanced surveillance since 2016, 18 free-ranging reindeers have been diagnosed in Norway along with three cases in moose (Alces alces), and a case in red deer (Cervus elaphus atlanticus) from a total of 39 496 cervids tested. Molecular analysis suggest that the reindeer prions detected are similar to findings from North America, while prions found in Norwegian moose and red deer have an atypical character. This raises important questions concerning the disease itself (origin, pathogenesis and transmissibility) as well as its future management. CWD research conducted at the Norwegian Veterinary Institute is currently focusing on disease progression and pathogenesis, diagnostics, epidemiology and genetics. We will present and update on the surveillance and disease status two years post discovery, along with future perspectives and a brief overview of the current research projects.

• Våge, Jørn; Madslien, Knut; Vikøren, Turid; Hopp, Petter; Viljugrein, Hildegunn & Neves, Carlos G Das [Vis alle 9 forfattere av denne artikkelen] (2018). CHRONIC WASTING DISEASE IN NORWAY: AN UPDATE ON SURVEILLANCE, RESEARCH AND DISEASE DEVELOPMENT. Fulltekst i vitenarkiv Vis sammendrag

  Chronic Wasting Disease (CWD) is an invariably fatal neurodegenerative disease of cervids, belonging to the group of transmissible spongiform encephalopathies. The disease is endemic in some areas in North America, with natural infection in different cervid species. Prior to 2016, CWD had never been reported outside North America, except in captive deer in South Korea introduced by import of CWD-infected animals. The surveillance for CWD in Europe has been limited. In Norway, approximately 2 100 cervids were tested for CWD in the period 2004-2015. Less than 20 of these were free-ranging reindeer (Rangifer tarandus tarandus). Norway is the last refugium for wild tundra reindeer in Europe that live in fragmented sub-populations in remote alpine regions of South Norway. In March 2016, a young adult female wild reindeer was diagnosed with CWD, representing the first detection of CWD in Europe and the first case of natural infection in reindeer worldwide. Since 2016, through enhanced surveillance, 18 free-ranging reindeers have been diagnosed in Norway along with three cases in moose (Alces alces), and one case in red deer (Cervus elaphus atlanticus) from a total of 39,496 cervids tested. Molecular analysis cannot differentiate the CWD-prions detected in reindeer from findings in North America, while prions found in Norwegian moose and red deer have an atypical character. This raises important questions concerning the disease itself (origin, pathogenesis and transmissibility) as well as its future management. CWD research conducted at the Norwegian Veterinary Institute is currently focusing on disease progression and pathogenesis, diagnostics, epidemiology and genetics. We will present and update on the surveillance and disease status two years post discovery, along with future perspectives and a brief overview of the current research projects.

• Våge, Jørn; Madslien, Knut; Vikøren, Turid; Hopp, Petter; Viljugrein, Hildegunn & Neves, Carlos G Das [Vis alle 9 forfattere av denne artikkelen] (2018). Chronic Wasting Disease in Norway: An update on surveillance, research and disease development. Fulltekst i vitenarkiv Vis sammendrag

  Norway Chronic Wasting Disease (CWD) is an invariably fatal neurodegenerative disease of cervids, belonging to the group of transmissible spongiform encephalopathies. The disease is endemic in some areas in North America, with natural infection in different cervid species. Prior to 2016, CWD had never been reported outside North America, except in captive deer in South Korea introduced by import of CWD-infected animals. The surveillance for CWD in Europe has been limited. In Norway, approximately 2 100 cervids were tested for CWD in the period 2004-2015. Less than 20 of these were free-ranging reindeer (Rangifer tarandus tarandus). Norway is the last refugium for wild tundra reindeer in Europe that live in fragmented sub-populations in remote alpine regions of South Norway. In March 2016, a young adult female wild reindeer was diagnosed with CWD, representing the first detection of CWD in Europe and the first case of natural infection in reindeer worldwide. Since 2016, through enhanced surveillance, 18 free-ranging reindeers have been diagnosed in Norway along with three cases in moose (Alces alces), and one case in red deer (Cervus elaphus atlanticus) from a total of 39,496 cervids tested. Molecular analysis cannot differentiate the CWD-prions detected in reindeer from findings in North America, while prions found in Norwegian moose and red deer have an atypical character. This raises important questions concerning the disease itself (origin, pathogenesis and transmissibility) as well as its future management. CWD research conducted at the Norwegian Veterinary Institute is currently focusing on disease progression and pathogenesis, diagnostics, epidemiology and genetics. We will present and update on the surveillance and disease status two years post discovery, along with future perspectives and a brief overview of the current research projects

• Helgesen, Kari Marie Olli; Kristoffersen, Anja Bråthen; Viljugrein, Hildegunn & Qviller, Lars (2018). Mer lakselus på våren -økt trussel mot vill laksesmolt og mot vekst i oppdrettsnæringa. Norsk veterinærtidsskrift. ISSN 0332-5741. 130(2), s. 95–96. Fulltekst i vitenarkiv
• Hopp, Petter; Viljugrein, Hildegunn; Benestad, Sylvie Lafond; Våge, Jørn; Rolandsen, Christer Moe & Mysterud, Atle (2018). Evaluating freedom of chronic wasting disease in wild reindeer populations accounting for differential sensitivity during the course of infection. Fulltekst i vitenarkiv
• Helgesen, Kari Marie Olli; Son, Thijs Christiaan van; Qviller, Lars; Kristoffersen, Anja Bråthen; Viljugrein, Hildegunn & Jansen, Peder A (2018). Hvordan forvalte rigide lusegrenser ved hjelp av usikre lusetall? Fulltekst i vitenarkiv
• Mysterud, Atle; Viljugrein, Hildegunn & Meisingset, Erling L. (2017). Hjortedyr, flått og Lyme borreliose. Hjorteviltet. ISSN 1502-3729. 22, s. 18–21. Fulltekst i vitenarkiv
• Hopp, Petter; Mysterud, Atle; Benestad, Sylvie Lafond; Vikøren, Turid & Viljugrein, Hildegunn (2017). Skrantesyke. Resultater av overvåkingen 2016. Fulltekst i vitenarkiv
• Helgesen, Kari Marie Olli; Son, Thijs Christiaan van; Kristoffersen, Anja Bråthen & Viljugrein, Hildegunn (2017). Better salmon lice management through improved understanding of salmon lice counts. Fulltekst i vitenarkiv
• Helgesen, Kari Marie Olli; Viljugrein, Hildegunn; Kristoffersen, Anja Bråthen; Qviller, Lars & Jansen, Peder A (2017). Lusekart og lusekalkulator. Fulltekst i vitenarkiv
• Helgesen, Kari Marie Olli; Kristoffersen, Anja Bråthen; Viljugrein, Hildegunn & Qviller, Lars (2017). Mer lakselus om våren -økt trussel mot vill laksesmolt og mot vekst i næringa. Norsk Fiskeoppdrett. ISSN 0332-7132. s. 50–51. Fulltekst i vitenarkiv
• Mysterud, Atle; Viljugrein, Hildegunn; Hopp, Petter; Rolandsen, Christer Moe & Nilsen, Erlend Birkeland (2017). Utbruddet av skrantesyke er et tidsskille i norsk naturforvaltning. Fulltekst i vitenarkiv
• Johnsen, Julie Føske; Viljugrein, Hildegunn; Bøe, Knut Egil; Gulliksen, Stine Margrethe; Beaver, Annabelle & Grøndahl, Ann Margaret [Vis alle 8 forfattere av denne artikkelen] (2016). Passive immunity of suckling calves and associations with colostrum management routines on organic dairy farms. Fulltekst i vitenarkiv
• Lyngstad, Trude Marie; Hellberg, Hege; Viljugrein, Hildegunn; Jensen, Britt Bang; Brun, Edgar & Tavornpanich, Saraya (2016). Fiskehelsetjenesetene - bærebjelken i overvåking av norsk fiskehelse. Norsk Fiskeoppdrett. ISSN 0332-7132. s. 60–65. Fulltekst i vitenarkiv
• Mysterud, Atle; Viljugrein, Hildegunn & Meisingset, Erling L. (2016). Flåttnytt. Fulltekst i vitenarkiv Vis sammendrag

  Flåttbårne sykdommer øker, men ikke bare på grunn av flere hjortedyr. "Forskning viser at..."

• Mysterud, Atle; Viljugrein, Hildegunn & Meisingset, Erling L. (2016). Flåttnytt. Flåttbårne sykdommer øker, men ikke bare på grunn av flere hjortedyr. s. 29–29. Fulltekst i vitenarkiv
• Gjevre, Anne Gerd; Grøntvedt, Randi & Viljugrein, Hildegunn (2015). Termisk avlusing av laks - dokumentasjon av velferd og effekt. Fulltekst i vitenarkiv
• Lyngstad, Trude Marie; Hellberg, Hege; Viljugrein, Hildegunn; Jensen, Britt Bang; Brun, Edgar & Sergeant, Evan [Vis alle 7 forfattere av denne artikkelen] (2015). Routine clinical inspections in marine salmonid farms have a high capability of detecting viral haemorrhagic septicaemia (VHS) and play a key role in surveillance for freedom. Fulltekst i vitenarkiv
• Vrålstad, Trude; Strand, David; Jussila, Japo; Johnsen, Stein Ivar; Viljamaa-Dirks, Satu & Edsman, Lennart [Vis alle 9 forfattere av denne artikkelen] (2014). Environmental DNA monitoring of the crayfish plague pathogen Aphanomyces astaci - news and views for research and management. Fulltekst i vitenarkiv Vis sammendrag

  Environmental DNA monitoring is increasingly used for detection and surveillance of diseases and invasive species in aquatic environments. Here, sampled water volumes and downstream analyses are imperative for successful detection of infrequent target organisms. We have studied the spore abundance of the crayfish plague pathogen Aphanomyces astaci (Oomycetes) in water bodies with resistant carrier signal crayfish compared to waters with susceptible noble crayfish suffering from crayfish plague. We tested two large scale filtering approaches (depth filtration and ultrafiltration, 5-100 L per sample, respectively) followed by A. astaci specific qPCR for spore quantification. Comparative analyses of crayfish and water samples demonstrated a significant positive association between A. astaci spore density in the water, pathogen prevalence in the corresponding crayfish population, and the crayfish tissue pathogen load. Signal crayfish areas typically contained low spore numbers, often less than one spore/L. In contrast, water samples from the outbreak area contained on average 43 times more A. Astaci spores/L. The sensitivity of the filtering techniques was evaluated using simulation of random events, and showed that an optimization of the spore recovery from ultrafiltration could yield a 10-fold increase in detection sensitivity. The monitoring approach is suitable for a range of research and management applications in nature and aquaculture, including studies of temporal and spatial sporulation dynamics, targeted disease surveillance, habitat evaluation prior to crayfish re-stockings, and water monitoring that can minimize disease transmission and spread. Our study emphasizes the need for optimized large volume filtering techniques for successful eDNAdetection of infrequent target organisms.

• Lindsø, Lars; Mysterud, Atle; Viljugrein, Hildegunn; Rivrud, Inger Maren & Anders, Jason Lee (2024). The role of small mammals in the enzootic cycle of Lyme disease in northern Europe. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Small mammals are important hosts to Ixodes ricinus larvae and maintain natural reservoirs of Borrelia afzelii, the most common genospecies of Borrelia-bacteria that causes Lyme disease in Europe. In my PhD project, I aimed to provide quantitative data on the role of small mammals as hosts to I. ricinus ticks and Borrelia-reservoirs to aid our understanding of Lyme disease emergence in northern Europe. By using data on pathogen infection in captured small mammals and their harboured ticks from Son, Vestby (2014-2022), I found that both tick infestations and pathogen infection prevalence in hosts increased markedly during the study period. The increase indicates a corresponding increase in the production of infected tick nymphs from fed and infected larvae, which in turn is directly linked to Lyme disease hazard for humans. Moreover, I found positive effects of warm years on the number of ticks on small mammals and that the proportion of infected hosts were lower in peak rodent years. Taken together, my thesis provides quantitative field-based evidence on the role of rodents and shrews in the Lyme disease cycle in northern Europe and provides important insights to explain the Lyme disease emergence in northern Europe in the last decades.

• Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie L.; Viljugrein, Hildegunn & Solberg, Erling Johan [Vis alle 14 forfattere av denne artikkelen] (2023). Kartlegging og overvåking av skrantesjuke (chronic wasting disease - CWD) 2022. Norsk institutt for naturforskning (NINA). ISSN 9788242650740. Fulltekst i vitenarkiv Vis sammendrag

  Norge, skrantesjuke, CWD, klassisk CWD, atypisk CWD, hjortedyr, elg, hjort, rådyr, villrein, tamrein, kartlegging

• Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie L.; Viljugrein, Hildegunn & Solberg, Erling Johan [Vis alle 15 forfattere av denne artikkelen] (2022). Kartlegging og overvåking av skrantesjuke (chronic wasting disease - CWD) 2021. Norsk institutt for naturforskning (NINA). ISSN 9788242649515. Fulltekst i vitenarkiv Vis sammendrag

  Norge, skrantesjuke, CWD, klassisk CWD, atypisk CWD, hjortedyr, elg, hjort, rådyr, villrein, tamrein, kartlegging

• Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie L.; Viljugrein, Hildegunn & Solberg, Erling Johan [Vis alle 16 forfattere av denne artikkelen] (2021). Kartlegging og overvåking av skrantesjuke (Chronic Wasting Disease - CWD) 2020. Norsk institutt for naturforskning (NINA). ISSN 9788242647610. Fulltekst i vitenarkiv Vis sammendrag

  Denne rapporten oppsummerer arbeidet som er gjennomført i 2020 for å kartlegge forekomsten av CWD, etter at sykdommen ble påvist hos villrein og elg i 2016. Den oppsummerer også totalt antall hjortedyr som er testet i perioden 2016-2020. I 2020 ble 22 527 hjortedyr testet for CWD, og myndighetenes mål om testing av 22 000 hjortedyr ble dermed nådd. I løpet av året ble det påvist ett tilfelle av klassisk CWD hos en 8 år gammel villreinbukk på Hardangervidda og ett nytt tilfelle av atypisk CWD hos en 17 år gammel elgku i Steinkjer kommune. Totalt er det i perioden 2016-2020 påvist klassisk CWD hos 20 villrein, og atypisk CWD hos sju elgkyr og ei hjortekolle. Prøvetakingen i 2020 omfattet som tidligere både hjerneprøve og lymfeknuter (primært svelglymfeknuter). Av de innsamlede prøvene inneholdt 72 % begge vevstypene. Dette er noe lavere enn i 2019 og 2018 med henholdsvis 78 % og 80 %. Selv om det har vært god oppslutning om prøveinnsamlingen og det er et høyt antall testede dyr, er det utfordringer med dårlig kvalitet på en god del prøver og det er problemer med mangelfull registrering. For eksempel var 3 % av prøvene ikke merket med kommune eller område, 2 % manglet informasjon om art, og for 9 % av ville hjortedyr manglet informasjon om prøven kom fra jakt eller fallvilt. I 2020 ble det testet i overkant av 20 % av registrerte fallvilt av viltlevende hjortedyr, noe som er en lavere andel enn ønsket. I gjennomsnitt ble over 80 % av felte villrein i de ulike villreinområdene testet, men bare for 67 % av disse ble det sendt inn både hjerne og lymfeknute. Med prøver fra både lymfeknute og hjerne vil det ta kortere tid å få kunnskap om forekomst og prevalens i områder med smitte og vi kan raskere sannsynliggjøre fravær av CWD i områder uten smitte. Fremover er det viktig å avklare om klassisk CWD forekommer i andre områder, og særlig i områder nær Nordfjella og Hardangervidda. Et stort antall prøver er dessuten viktig for å øke kunnskapen om forekomsten av atypisk CWD hos hjortedyr. Kunnskapen som er ervervet så langt viser at det er viktig å kjenne alder på dyrene. Dette gjelder både for klassisk og atypisk CWD. Hjorter og elger fra Fennoskandia med påvist atypisk CWD har vært gamle dyr. Det er derfor fortsatt ønskelig å aldersbestemme hjortevilt i utvalgte områder de neste årene, både fallvilt og dyr som felles under jakta. Med bedre kunnskap om aldersfordelingen kan vi med større sikkerhet beregne forekomst av atypisk CWD, og eventuelt også klassisk CWD, i ulike bestander.

• Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie Lafond; Viljugrein, Hildegunn & Solberg, Erling Johan [Vis alle 17 forfattere av denne artikkelen] (2020). Kartlegging og overvåking av skrantesjuke (Chronic Wasting Disease - CWD) 2016-2019. Norsk institutt for naturforskning (NINA). ISSN 9788242645777. Fulltekst i vitenarkiv Vis sammendrag

  Denne rapporten oppsummerer arbeidet som er gjennomført i 2019 for å kartlegge forekomsten av CWD, etter at sykdommen ble påvist hos villrein og elg i henholdsvis mars og mai 2016. Den oppsummerer også totalt antall hjortedyr som er testet i perioden 2016-2019. I 2019 ble 30 147 hjortedyr testet for CWD, og dermed ble myndighetenes mål om testing av 30 000 hjortedyr nådd. I 2019 ble det påvist to nye tilfeller av atypisk CWD, først hos en 20 år gammel elgku i Selbu kommune og senere hos en 12 år gammel elgku i Sigdal kommune. Totalt er det nå påvist atypisk CWD hos seks elgkyr og ei hjortekolle. Klassisk CWD er fortsatt kun funnet hos villrein fra sone 1 i Nordfjella villreinområde 2016-2018. Prøvetakingen i 2019 omfattet som i 2018 og tidligere, både hjerneprøve og lymfeknuter (primært svelglymfeknuter). Begge vevstypene var inkludert i 78 % av de innsamlede prøvene. Dette er omtrent på samme nivå som i 2018 (80 %). I det store og hele har innsamlingen vært preget av god oppslutning. Selv om det er tilfredshet med det høye antall testede dyr, er det utfordringer med innsendt vev av mangelfull kvalitet og med mangelfull registrering. For eksempel var 1,9 % av prøvene ikke merket med kommune eller område, 1,5 % manglet informasjon om art, og for 10,9 % av ville hjortedyr manglet informasjon om prøven kom fra jakt eller fallvilt. Andel fallvilt som er prøvetatt er lavere enn ønsket. Fremover er det spesielt viktig å avklare om klassisk CWD er tilstede i andre områder, og særlig i områdene nær Nordfjella. Et stort antall prøver er dessuten viktig for å utrede graden av smittsomhet for de tilfellene med CWD hos elg og hjort med atypiske karakteristika. Hos disse kan ikke smittestoff påvises i lymfeknutene. Dette til sammenlikning med CWD hos villrein, der man finner prioner også i lymfatisk vev. Kunnskapen vi har ervervet de tre siste årene viser hvor viktig det er å kjenne til alderen på dyrene som testes for CWD. Dette gjelder både for klassisk og atypisk CWD. Hjorten og elgene fra Fennoskandia med påvist atypisk CWD har vært gamle hunndyr. Som følge av denne kunnskapen, er det de neste årene ønskelig å aldersbestemme et større antall av hjorteviltet som testes for CWD, enn hva som er gjort tidligere. For fallvilt av elg, hjort, rådyr og rein er det aldri gjennomført systematiske aldersbestemmelser basert på tannsnitt. Fallvilt representerer en viktig risikogruppe for å avdekke sykdom i viltbestander. Med bedre kunnskap om aldersfordelingen hos fallvilt og felte dyr, vil det med større sikkerhet kunne beregnes forekomst av atypisk CWD, og eventuelt også klassisk CWD, dersom denne skulle dukke opp i nye bestander. I de neste 23 årene av kartleggingsprogrammet har NINA og Veterinærinstituttet derfor foreslått økt omfang på aldersanalyser av dyr som testes for CWD, både av fallvilt og dyr felt under jakt. Dette vil kunne gi et bedre kunnskapsgrunnlag for fremtidig kartlegging av CWD. I 2020 har myndighetene redusert målet om antall prøver fra 30 000 til 22 000. Dette skyldes i hovedsak at Mattilsynet i flere områder vil redusere testingen av tamrein fordi det her allerede har blitt testet et så høyt antall dyr tidligere år. Antall prøver av viltlevende elg og hjort som felles under jakt samt testing av slakt av oppdrettshjort, skal opprettholdes på omtrent samme nivå som i 2019. For fallvilt av både ville og tamme hjortedyr, er målet å få inn prøver fra så mange som mulig, kun med unntak av de som blir funnet så lenge etter dødstidspunktet at prøven ikke er egnet til undersøkelser.

• Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie Lafond; Viljugrein, Hildegunn & Solberg, Erling Johan [Vis alle 16 forfattere av denne artikkelen] (2019). Kartlegging av skrantesjuke (CWD) i 2016-2018. Norsk institutt for naturforskning (NINA). ISSN 9788242634610. Fulltekst i vitenarkiv Vis sammendrag

  Skrantesjuke (Chronic Wasting Disease - CWD) ble oppdaget hos villrein (Rangifer tarandus) og elg (Alces alces) våren 2016, og hos hjort (Cervus elaphus) høsten 2017. Dette var første gang sykdommen ble påvist i Europa. CWD forårsakes av opphopning av feilfoldede prionproteiner i hjernen og nervesystemet. Den klassiske formen for CWD er smittsom, alltid dødelig, og har evne til å spre seg mellom hjortedyrarter. Alvorlighetsgraden av denne sykdommen medførte at Mattilsynet og Miljødirektoratet initierte et storstilt nasjonalt prøvetakingsarbeid fra hjortedyr. Norsk institutt for naturforskning (NINA) og Veterinærinstituttet fikk ansvaret for å organisere innsamlingsarbeidet og gjennomføre nødvendige analyser av det innsamlede materialet. Ved utgangen av 2017 var det analysert prøver fra 35 794 individer. Flere funn av klassisk (smittsom) CWD hos villrein fra sone 1 i Nordfjella villreinområde, medførte statlig vedtak om å skyte ut hele denne delbestanden. Dette ble gjennomført vinteren 2017/2018. Ved inngangen til 2018 var det registrert 13 tilfeller av CWD hos villrein, tre tilfeller hos elg og ett tilfelle hos hjort. Tilfellene hos elg og hjort ble klassifisert som atypisk CWD. Dette er en type av sykdommen som trolig oppstår spontant, primært hos eldre individer, og som antas å ikke være smittsom, eller i så fall, ikke i samme grad som klassisk CWD. Innsamlingsarbeidet i 2018 avdekket ytterligere seks funn av klassisk CWD hos villrein. Alle disse stammet fra den statlige fellingen i Nordfjella sone 1. Det ble også funnet en elgku med atypisk CWD i Flesberg kommune i Buskerud. Arbeidet med å kartlegge forekomsten av CWD hos norske hjortedyr ble ytterligere intensivert i 2018. En medvirkende årsak til opptrappingen var EUs vedtak om å initiere et europeisk kartleggingsprogram. I 2018 ble det organisert innsamling av hjerneprøve og lymfeknuter fra elg, hjort og villrein felt under ordinær jakt i 125 kommuner, 21 villreinområder, og viltbehandlingsanlegg spredt rundt i landet. Innsamlingen ble utført av jegere på felte dyr. I tillegg ble alle landets kommuner bedt om å samle prøver fra fallvilt fra alle hjorteviltarter. Det ble også tatt prøver av slaktet tamrein fra 65 av landets 83 reinbeitedistrikter og fra annet oppdrettet hjortevilt (hjort, dåhjort). Myndighetenes mål for 2018 var prøver fra 30 000 individer. Formålet med innsamlingen var å få mer kunnskap om forekomst og geografisk utbredelse av CWD i Norge. Takket være en formidabel innsats fra jegere og representanter fra kommuner, villreinnemder, villreinutvalg, fjelloppsyn m.m., ble innsamlingsarbeidet i 2018 svært vellykket. Totalt ble det samlet inn og analysert prøver fra 33 656 hjortedyr. Av dette stammet prøvene fra 16 400 individer felt under jakt, 12 461 individer fra slaktet tamrein og 3743 individer fra fallvilt. I tillegg stammet 1052 prøver fra individer med ukjent opprinnelse. Prøvetakingen i 2018 omfattet både hjerneprøve og lymfeknuter (primært svelglymfeknuter). Over 80 % av de innsamlede prøvene inneholdt begge vevstypene. Dette er en vesentlig økning fra tidligere år. I 2018 har det også vært utøvd betydelig innsats fra Miljødirektoratet, Veterinærinstituttet og NINA med tilrettelegging av funksjonelle merkesystemer og løsninger for innsamling av individdata, rapportering av analyseresultater og informasjonsvirksomhet. Eksisterende løsninger fungerer godt, og sørger for god sporbarhet og rask resultatformidling. Det er imidlertid fortsatt forbedringspotensial med hensyn til ufullstendig merking av prøver og fortsatt utfordringer med varierende kvalitet på hjerneprøver som sendes inn. I 2019 er det myndighetens mål å opprettholde omfanget av overvåkingen på samme nivå som i 2018. Dette vil gjøres innenfor rammer definert av Mattilsynet og Miljødirektoratet.

• Bernhoft, Aksel; Torget, Vidar; Vikøren, Turid; Ørnsrud, Robin; Lyche, Jan Ludvig & Sandvik, Morten [Vis alle 10 forfattere av denne artikkelen] (2018). Miljøgifter i hubro i Norge 1994-2014 - Rottegifter, klororganiske forbindelser og toksiske metaller. Veterinærinstituttet. Fulltekst i vitenarkiv
• Rolandsen, Christer Moe; Våge, Jørn; Hopp, Petter; Benestad, Sylvie Lafond; Mysterud, Atle & Viljugrein, Hildegunn [Vis alle 17 forfattere av denne artikkelen] (2018). Kartlegging av skrantesjuke (CWD) i 2016 og 2017. Norsk institutt for naturforskning (NINA). ISSN 9788242632609. Fulltekst i vitenarkiv
• Kristoffersen, Anja Bråthen; Qviller, Lars; Viljugrein, Hildegunn; Helgesen, Kari Marie Olli & Jansen, Peder A (2017). Produksjon av lakselus i oppdrett, estimert lusepåslag og vurdering av luseindusert dødelighet for villaks innen produksjonsområder for oppdrettslaks. Veterinærinstituttet. Fulltekst i vitenarkiv
• Kristoffersen, Anja Bråthen; Qviller, Lars; Viljugrein, Hildegunn; Helgesen, Kari Marie Olli & Jansen, Peder A (2017). Risikomodell for kvantifisering av luseindusert dødelighet på villaks. Veterinærinstituttet. Fulltekst i vitenarkiv
• Son, TC van; Kristoffersen, Anja Bråthen; Viljugrein, Hildegunn; Helgesen, Kari Marie Olli; Qviller, Lars & Jansen, Peder A (2016). Forslag til håndtering av falske positive og negative lusetellinger ved lave lusetall. Veterinærinstituttets rapportserie. Fulltekst i vitenarkiv
• Gismervik, Kristine; Østvik, Asgeir & Viljugrein, Hildegunn (2016). Pilotflåte Helixir-dokumentasjon av fiskevelferd og effekt mot lus. Del 1 uten legemiddel. Veterinærinstituttet. Fulltekst i vitenarkiv
• Grøntvedt, Randi; Nerbøvik, IKG; Viljugrein, Hildegunn; Lillehaug, Atle; Nilsen, Hanne Katrine & Gjevre, Anne Gerd (2015). Termisk avlusning av laksefisk - dokumentasjon av fiskevelferd og effekt. Veterinærinstituttet. Fulltekst i vitenarkiv

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