William Ryan Easterday

• 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.

• Nilsson, Pernille; Ravinet, Mark; Cui, Yujun; Berg, Paul Ragnar; Zhang, Yujiang & Guo, Rong [Vis alle 17 forfattere av denne artikkelen] (2022). Polygenic plague resistance in the great gerbil uncovered by population sequencing. PNAS Nexus. 1(5). doi: 10.1093/pnasnexus/pgac211. Fulltekst i vitenarkiv
• Nilsson, Pernille; Solbakken, Monica Hongrø; Schmid, Boris Valentijn; Orr, Russell; Lv, Ruichen & Cui, Yujun [Vis alle 15 forfattere av denne artikkelen] (2020). The Genome of the Great Gerbil Reveals Species-Specific Duplication of an MHCII Gene. Genome Biology and Evolution (GBE). 12(2), s. 3832–3849. doi: 10.1093/gbe/evaa008. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The great gerbil (Rhombomys opimus) is a social rodent living in permanent, complex burrow systems distributed throughout Central Asia, where it serves as the main host of several important vector-borne infectious pathogens including the well-known plague bacterium (Yersinia pestis). Here, we present a continuous annotated genome assembly of the great gerbil, covering over 96% of the estimated 2.47-Gb genome. Taking advantage of the recent genome assemblies of the sand rat (Psammomys obesus) and the Mongolian gerbil (Meriones unguiculatus), comparative immunogenomic analyses reveal shared gene losses within TLR gene families (i.e., TLR8, TLR10, and the entire TLR11-subfamily) for Gerbillinae, accompanied with signs of diversifying selection of TLR7 and TLR9. Most notably, we find a great gerbil-specific duplication of the MHCII DRB locus. In silico analyses suggest that the duplicated gene provides high peptide binding affinity for Yersiniae epitopes as well as Leishmania and Leptospira epitopes, putatively leading to increased capability to withstand infections by these pathogens. Our study demonstrates the power of whole-genome sequencing combined with comparative genomic analyses to gain deeper insight into the immunogenomic landscape of the great gerbil and its close relatives.

• Cui, Yujun; Schmid, Boris Valentijn; Cao, Hanli; Dai, Xiang; Du, Zhongmin & Easterday, William Ryan [Vis alle 24 forfattere av denne artikkelen] (2020). Evolutionary selection of biofilm-mediated extended phenotypes in Yersinia pestis in response to a fluctuating environment. Nature Communications. 11, s. 1–8. doi: 10.1038/s41467-019-14099-w. Fulltekst i vitenarkiv Vis sammendrag

  Yersinia pestis is transmitted from fleas to rodents when the bacterium develops an extensive biofilm in the foregut of a flea, starving it into a feeding frenzy, or, alternatively, during a brief period directly after feeding on a bacteremic host. These two transmission modes are in a trade-off regulated by the amount of biofilm produced by the bacterium. Here by investigating 446 global isolated Y. pestis genomes, including 78 newly sequenced isolates sampled over 40 years from a plague focus in China, we provide evidence for strong selection pressures on the RNA polymerase ω-subunit encoding gene rpoZ. We demonstrate that rpoZ variants have an increased rate of biofilm production in vitro, and that they evolve in the ecosystem during colder and drier periods. Our results support the notion that the bacterium is constantly adapting—through extended phenotype changes in the fleas—in response to climate-driven changes in the niche.

• Easterday, William Ryan; Ponciano, José Miguel; Gomez, Juan Pablo; Ert, Matthew N. Van; Hadfield, Ted & Bagamian, Karoun [Vis alle 9 forfattere av denne artikkelen] (2020). Coalescence modeling of intrainfection Bacillus anthracis populations allows estimation of infection parameters in wild populations. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 117(8), s. 4273–4280. doi: 10.1073/pnas.1920790117. Fulltekst i vitenarkiv Vis sammendrag

  Bacillus anthracis, the etiological agent of anthrax, is a well-established model organism. For B. anthracis and most other infectious diseases, knowledge regarding transmission and infection parameters in natural systems, in large part, comprises data gathered from closely controlled laboratory experiments. Fatal, natural anthrax infections transmit the bacterium through new host−pathogen contacts at carcass sites, which can occur years after death of the previous host. For the period between contact and death, all of our knowledge is based upon experimental data from domestic livestock and laboratory animals. Here we use a noninvasive method to explore the dynamics of anthrax infections, by evaluating the terminal diversity of B. anthracis in anthrax carcasses. We present an application of population genetics theory, specifically, coalescence modeling, to intrainfection populations of B. anthracis to derive estimates for the duration of the acute phase of the infection and effective population size converted to the number of colony-forming units establishing infection in wild plains zebra (Equus quagga). Founding populations are small, a few colony-forming units, and infections are rapid, lasting roughly between 1 d and 3 d in the wild. Our results closely reflect experimental data, showing that small founding populations progress acutely, killing the host within days. We believe this method is amendable to other bacterial diseases from wild, domestic, and human systems.

• Bruce, Spencer A; Schiraldi, Nicholas J; Kamath, Pauline L.; Easterday, William Ryan & Turner, Wendy C. (2019). A classification framework for Bacillus anthracis defined by global genomic structure. Evolutionary Applications. s. 1–10. doi: 10.1111/eva.12911. Fulltekst i vitenarkiv Vis sammendrag

  Bacillus anthracis , the causative agent of anthrax, is a considerable global health threat affecting wildlife, livestock, and the general public. In this study, whole‐genome sequence analysis of over 350 B. anthracis isolates was used to establish a new high‐resolution global genotyping framework that is both biogeographically informative and compatible with multiple genomic assays. The data presented in this study shed new light on the diverse global dissemination of this species and indicate that many lineages may be uniquely suited to the geographic regions in which they are found. In addition, we demonstrate that plasmid genomic structure for this species is largely consistent with chromosomal population structure, suggesting vertical inheritance in this bacterium has contributed to its evolutionary persistence. This classification methodology is the first based on population genomic structure for this species and has potential use for local and broader institutions seeking to understand both disease outbreak origins and recent introductions. In addition, we provide access to a newly developed genotyping script as well as the full whole‐genome sequence analyses output for this study, allowing future studies to rapidly employ and append their data in the context of this global collection. This framework may act as a powerful tool for public health agencies, wildlife disease laboratories, and researchers seeking to utilize and expand this classification scheme for further investigations into B. anthracis evolution.

• Carlson, Colin; Getz, Wayne M.; Kausrud, Kyrre Linné; Cizauskas, Carrie A.; Blackburn, Jason K. & Carrillo, Fausto A Bustos [Vis alle 14 forfattere av denne artikkelen] (2018). Spores and soil from six sides: interdisciplinarity and the environmental biology of anthrax (Bacillus anthracis). Biological Reviews. ISSN 1464-7931. 93(4), s. 1813–1831. doi: 10.1111/brv.12420. Fulltekst i vitenarkiv
• 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.

• Valseth, Karoline; Nesbø, Camilla Lothe; Easterday, William Ryan; Turner, Wendy Christine; Olsen, Jaran Strand & Stenseth, Nils Christian [Vis alle 7 forfattere av denne artikkelen] (2017). Temporal dynamics in microbial soil communities at anthrax carcass sites. BMC Microbiology. doi: 10.1186/s12866-017-1111-6. Fulltekst i vitenarkiv Vis sammendrag

  BackgroundAnthrax is a globally distributed disease affecting primarily herbivorous mammals. It is caused by the soil-dwelling and spore-forming bacterium Bacillus anthracis. The dormant B. anthracis spores become vegetative after ingestion by grazing mammals. After killing the host, B. anthracis cells return to the soil where they sporulate, completing the lifecycle of the bacterium. Here we present the first study describing temporal microbial soil community changes in Etosha National Park, Namibia, after decomposition of two plains zebra (Equus quagga) anthrax carcasses. To circumvent state-associated-challenges (i.e. vegetative cells/spores) we monitored B. anthracis throughout the period using cultivation, qPCR and shotgun metagenomic sequencing. ResultsThe combined results suggest that abundance estimation of spore-forming bacteria in their natural habitat by DNA-based approaches alone is insufficient due to poor recovery of DNA from spores. However, our combined approached allowed us to follow B. anthracis population dynamics (vegetative cells and spores) in the soil, along with closely related organisms from the B. cereus group, despite their high sequence similarity. Vegetative B. anthracis abundance peaked early in the time-series and then dropped when cells either sporulated or died. The time-series revealed that after carcass deposition, the typical semi-arid soil community (e.g. Frankiales and Rhizobiales species) becomes temporarily dominated by the orders Bacillales and Pseudomonadales, known to contain plant growth-promoting species. ConclusionOur work indicates that complementing DNA based approaches with cultivation may give a more complete picture of the ecology of spore forming pathogens. Furthermore, the results suggests that the increased vegetation biomass production found at carcass sites is due to both added nutrients and the proliferation of microbial taxa that can be beneficial for plant growth. Thus, future B. anthracis transmission events at carcass sites may be indirectly facilitated by the recruitment of plant-beneficial bacteria.

• 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.

• Turner, Wendy Christine; Kausrud, Kyrre Linné; Beyer, Wolfgang; Easterday, William Ryan; Barandongo, Zoe R. & Blaschke, Elisabeth [Vis alle 13 forfattere av denne artikkelen] (2016). Lethal exposure: An integrated approach to pathogen transmission via environmental reservoirs. Scientific Reports. 6. doi: 10.1038/srep27311. Fulltekst i vitenarkiv
• Valseth, Karoline; Nesbø, Camilla Lothe; Easterday, William Ryan; Turner, Wendy Christine; Olsen, Jaran Strand & Stenseth, Nils Christian [Vis alle 7 forfattere av denne artikkelen] (2016). Draft Genome Sequences of Two Bacillus anthracis Strains from Etosha National Park, Namibia. Microbiology Resource Announcements (MRA). 4(4). doi: 10.1128/genomeA.00861-16. Fulltekst i vitenarkiv
• Schmid, Boris Valentijn; Büntgen, Ulf; Easterday, William Ryan; Ginzler, Christian; Walløe, Lars & Bramanti, Barbara [Vis alle 7 forfattere av denne artikkelen] (2015). Climate-driven introduction of the Black Death and successive plague reintroductions into Europe. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 112(10), s. 3020–3025. doi: 10.1073/pnas.1412887112. Fulltekst i vitenarkiv
• Mysterud, Atle; Easterday, William Ryan; Qviller, Lars; Viljugrein, Hildegunn & Ytrehus, Bjørnar (2013). Spatial and seasonal variation in the prevalence of Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato in questing Ixodes ricinus ticks in Norway. Parasites & Vectors. 6(187). doi: 10.1186/1756-3305-6-187. Fulltekst i vitenarkiv Vis sammendrag

  Background. Understanding the variation in prevalence of Borrelia burgdorferi sensu lato (Lyme Borreliosis Spirochaetes, LBS) and Anaplasma phagocytophilum (causing tick-borne fever in ruminants and human granulocytic ehrlichiosis) in ticks is vital from both a human and an animal disease perspective to target the most effective mitigation measures. From the host competence hypothesis, we predicted that prevalence of LBS would decrease with red deer density, while prevalence of A. phagocytophilum would increase. Methods. Based on a sample of 112 adult and 686 nymphal Ixodes ricinus ticks collected with flagging during questing from 31 transects (4–500 m long) corresponding to individual seasonal home ranges of 41 red deer along the west coast of Norway, we tested whether there were spatial and seasonal variations in prevalence with a special emphasis on the population density of the most common large host in this area, the red deer (Cervus elaphus). We used a multiplex real-time PCR assay for detection of A. phagocytophilum and LBS. Results. Prevalence of LBS was higher in adult female ticks (21.6%) compared to adult male ticks (11.5%) and nymphs (10.9%), while prevalence was similar among stages for prevalence of A. phagocytophilum (8.8%). Only partly consistent with predictions, we found a lower prevalence of LBS in areas of high red deer density, while there was no relationship between red deer density and prevalence of A. phagocytophilum in ticks. Prevalence of both bacteria was much higher in ticks questing in May compared to August. Conclusions. Our study provides support to the notion that spatial variation in host composition forms a role for prevalence of LBS in ticks also in a northern European ecosystem, while no such association was found for A. phagocytophilum. Further studies are needed to fully understand the similar seasonal pattern of prevalence of the two pathogens.

• Easterday, William Ryan; Kausrud, Kyrre Linné; Star, Bastiaan; Heier, Lise; Haley, B. J. & Ageyev, Vladimir [Vis alle 8 forfattere av denne artikkelen] (2012). An additional step in the transmission of Yersinia pestis? The ISME Journal. ISSN 1751-7362. 6(2), s. 231–236. doi: 10.1038/ismej.2011.105. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Kausrud, Kyrre; Lagesen, Karin; Easterday, William Ryan; Whittington, Jason; Turner, Wendy Christine & Wolff, Cecilia Mia [Vis alle 8 forfattere av denne artikkelen] (2021). How much time have we got? ARPHA Conference Abstracts. doi: 10.3897/aca.4.e68934. Fulltekst i vitenarkiv
• Kausrud, Kyrre; Turner, Wendy C.; Easterday, William Ryan; Feiring, Marie; Skjerdal, Taran & Whittington, Jason [Vis alle 11 forfattere av denne artikkelen] (2021). Evolving at the speed of risk. Fulltekst i vitenarkiv
• Easterday, William Ryan; Muinck, Eric de & Stigum, Vetle Malmer (2021). the not so straight-forward way of generating long reads on the PacBio. Fulltekst i vitenarkiv
• Nave, Oline Birgitte & Easterday, William Ryan (2020). Kaldere vær og mer innetid: Slik kan corona-høsten bli. [Journal]. https://www.vg.no/nyheter/innenriks/i/vAm8aX/kaldere-vaer-og. Fulltekst i vitenarkiv
• Easterday, William Ryan (2020). The first step in the success or failure of emerging pathogens. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. doi: 10.1073/pnas.2020709117. Fulltekst i vitenarkiv
• Røsjø, Bjarne & Easterday, William Ryan (2020). Hvor mange korona-virus trengs for å gjøre deg syk? [Internet]. https://titan.uio.no/livsvitenskap-naturvitenskap-medisin/20. Fulltekst i vitenarkiv
• Freid, David & Easterday, William Ryan (2017). Nobody Dies in Longyearbyen. [Internet]. https://www.youtube.com/watch?v=lyrjDpkX6nA. Fulltekst i vitenarkiv
• Mjønes, Caroline Skar; Easterday, William Ryan & Mysterud, Atle (2014). Developing a targeted method for capturing DNA from ticks for genome sequencing of Borrelia. Fulltekst i vitenarkiv
• Nilsson, Pernille; Easterday, William Ryan; Schmid, Boris Valentijn; Jentoft, Sissel; Jakobsen, Kjetill Sigurd & Zhange, Yujiang [Vis alle 8 forfattere av denne artikkelen] (2014). Plague and the Chinese experience – how to collaborate and work in China. Fulltekst i vitenarkiv
• Cloete, Claudine Catherine; Kausrud, Kyrre Linné; Easterday, William Ryan; Turner, Wendy Christine & Stenseth, Nils Christian (2014). Climate fluctuations and zoonotic diseases – The case of anthrax in Etosha National Park. Fulltekst i vitenarkiv
• Schmid, Boris Valentijn; Buntgen, U; Easterday, William Ryan; Ginzler, Christian; Walløe, Lars & Bramanti, Barbara [Vis alle 7 forfattere av denne artikkelen] (2013). The pulse of Asia: The Black Death and successive reintroductions of plague into Europe. Fulltekst i vitenarkiv
• Kausrud, Kyrre Linné; Боровая, Наталья; Easterday, William Ryan; Star, Bastiaan & Ageyev, Vladimir (2010). Умы против чумы. [Journal]. Almaty, Kazakhstan. Fulltekst i vitenarkiv Vis sammendrag

  Свидание с дикой природой, будь то леса, горы, степи и пустыни, оставляет неизгладимый след в душе человека. Вглядываясь в ночное небо, усыпанное мириадами звёзд, он ощущает себя крохотной частицей миро-здания, задумывается о вечности и своём месте во Вселенной. Ночные за-пахи, шорохи и слабое дуновение ветра ока- зывают усыпляющее действие, и путник плавно погружается в блаженный сон. Однако не всегда природа бы- вает ласковой матерью для человека. Незнание медико-биологических особенностей посещаемой территории и забвение элементарных правил поведения на местности может привести к непоправимым последствиям.

• Aas, Anders Bjørnsgaard; Davey, Marie Louise; Kauserud, Håvard; Easterday, William Ryan & Brysting, Anne Krag (2017). Root-associated microbes: Spatial Oddities and Methodological Perspectives. Universitetet i Oslo. Fulltekst i vitenarkiv

Se alle arbeider i NVA