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1. The changing ecology of primate parasites: Insights from wild‐captive comparisons

   https://doi.org/10.1002/ajp.22991  

   Herrera, James P. ; Chakraborty, Debapriyo ; Rushmore, Julie ; Altizer, Sonia ; Nunn, Charles ( July 2019 , American Journal of Primatology)

   Host movements, including migrations or range expansions, are known to influence parasite communities. Transitions to captivity—a rarely studied yet widespread human‐driven host movement—can also change parasite communities, in some cases leading to pathogen spillover among wildlife species, or between wildlife and human hosts. We compared parasite species richness between wild and captive populations of 22 primate species, including macro‐ (helminths and arthropods) and micro‐parasites (viruses, protozoa, bacteria, and fungi). We predicted that captive primates would have only a subset of their native parasite community, and would possess fewer parasites with complex life cycles requiring intermediate hosts or vectors. We further predicted that captive primates would have parasites transmitted by close contact and environmentally—including those shared with humans and other animals, such as commensals and pests. We found that the composition of primate parasite communities shifted in captive populations, especially because of turnover (parasites detected in captivity but not reported in the wild), but with some evidence of nestedness (holdovers from the wild). Because of the high degree of turnover, we found no significant difference in overall parasite richness between captive and wild primates. Vector‐borne parasites were less likely to be found in captivity, whereas parasites transmitted through either close or non‐close contact, including through fecal‐oral transmission, were more likely to be newly detected in captivity. These findings identify parasites that require monitoring in captivity and raise concerns about the introduction of novel parasites to potentially susceptible wildlife populations during reintroduction programs.

    

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2. Re‐emphasizing mechanism in the community ecology of disease

   https://doi.org/10.1111/1365-2435.13892  

   Shaw, Kelsey E. ; Civitello, David J. ( September 2021 , Functional Ecology)

   Hosts and their parasites exist within complex ecological communities. However, the role that non‐focal community members, species which cannot be infected by a focal pathogen, may play in altering parasite transmission is often only studied in the lens of the ‘diversity‐disease’ relationship by focusing on species richness. This approach largely ignores mechanistic species interactions and risks collapsing our understanding of the community ecology of disease down to defining the prominence of ‘amplification’ versus ‘dilution’ effects.

   However, non‐focal species vary in their traits, densities and types of interactions with focal hosts and parasites. Therefore, a community ecology approach based on the mechanisms underlying parasite transmission, host harm and dynamic species interactions may better advance our understanding of parasite transmission in complex communities.

   Using the concept of the parasite's basic reproductive ratio,R₀, as a generalizable framework, we examine several critical mechanisms by which interactions among hosts, parasites and non‐focal species modulate transmission and provide examples from relevant literature.

   By focusing on the mechanism by which non‐focal species impact transmission, we can emphasize the similarities among classic paradigms in the community ecology of disease, gain new insights into parasite invasion and persistence, better predict community traits correlated with disease dilution or amplification, and gauge the feasibility of biocontrol for parasites of conservation, agricultural or human health concern.

   A freePlain Language Summarycan be found within the Supporting Information of this article.

    

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3. Host blood meal identity modifies vector gene expression and competency

   https://doi.org/10.1111/mec.16413  

   Ring, Kacie ; Couper, Lisa I. ; Sapiro, Anne L. ; Yarza, Fauna ; Yang, X. Frank ; Clay, Keith ; Mateusiak, Chase ; Chou, Seemay ; Swei, Andrea ( January 2022 , Molecular Ecology)

   A vector's susceptibility and ability to transmit a pathogen—termed vector competency—determines disease outcomes, yet the ecological factors influencing tick vector competency remain largely unknown. Ixodes pacificus, the tick vector of Borrelia burgdorferi (Bb) in the western U.S., feeds on rodents, birds, and lizards. Rodents and birds are reservoirs for Bb and infect juvenile ticks, while lizards are refractory to Bb and cannot infect feeding ticks. Additionally, the lizard bloodmeal contains borreliacidal properties, clearing previously infected feeding ticks of their Bb infection. Despite I. pacificus feeding on a range of hosts, it is undetermined how the host identity of the larval bloodmeal affects future nymphal vector competency. We experimentally evaluate the influence of larval host bloodmeal on Bb acquisition by nymphal I. pacificus. Larval I. pacificus were fed on either lizards or mice and after molting, nymphs were fed on Bb-infected mice. We found that lizard-fed larvae were significantly more likely to become infected with Bb during their next bloodmeal than mouse-fed larvae. We also conducted the first RNA-seq analysis on whole-bodied I. pacificus and found significant upregulation of tick antioxidants and antimicrobial peptides in the lizard-fed group. Our results indicate that the lizard bloodmeal significantly alters vector competency and gene regulation in ticks, highlighting the importance of host bloodmeal identity in vector-borne disease transmission and upends prior notions about the role of lizards in Lyme disease community ecology. 

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4. Multimodal pathogen transmission as a limiting factor in host distribution

   https://doi.org/10.1002/ecy.3956  

   Uricchio, Lawrence H. ; Bruns, Emily L. ; Hood, Michael E. ; Boots, Mike ; Antonovics, Janis ( January 2023 , Ecology)

   Theoretical models suggest that infectious diseases could play a substantial role in determining the spatial extent of host species, but few studies have collected the empirical data required to test this hypothesis. Pathogens that sterilize their hosts or spread through frequency‐dependent transmission could have especially strong effects on the limits of species' distributions because diseased hosts that are sterilized but not killed may continue to produce infectious stages and frequency‐dependent transmission mechanisms are effective even at very low population densities. We collected spatial pathogen prevalence data and population abundance data for alpine carnations infected by the sterilizing pathogenMicrobotryum dianthorum, a parasite that is spread through both frequency‐dependent (vector‐borne) and density‐dependent (aerial spore transmission) mechanisms. Our 13‐year study reveals rapid declines in population abundance without a compensatory decrease in pathogen prevalence. We apply a stochastic, spatial model of parasite spread that accommodates spatial habitat heterogeneity to investigate how the population dynamics depend on multimodal (frequency‐dependent and density‐dependent) transmission. We found that the observed rate of population decline could plausibly be explained by multimodal transmission, but is unlikely to be explained by either frequency‐dependent or density‐dependent mechanisms alone. Multimodal pathogen transmission rates high enough to explain the observed decline predicted that eventual local extinction of the host species is highly likely. Our results add to a growing body of literature showing how multimodal transmission can constrain species distributions in nature.

    

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5. Local community composition drives avian Borrelia burgdorferi infection and tick infestation

   https://doi.org/10.3390/vetsci9020055  

   Lilly, M. ; Amaya-Mejia, W. ; Pavan, L. ; Peng, C. ; Crews, A. ; Tran, N. ; Sehgal, R. ; Swei, A. ( January 2022 , Veterinary sciences)

   Globally, zoonotic vector-borne diseases are on the rise and understanding their complex transmission cycles is pertinent to mitigating disease risk. In North America, Lyme disease is the most commonly reported vector-borne disease and is caused by transmission of Borrelia burgdorferi sensu lato (s.l.) from Ixodes spp. ticks to a diverse group of vertebrate hosts. Small mammal reservoir hosts are primarily responsible for maintenance of B. burgdorferi s.l. across the United States. Never- theless, birds can also be parasitized by ticks and are capable of infection with B. burgdorferi s.l. but their role in B. burgdorferi s.l. transmission dynamics is understudied. Birds could be important in both the maintenance and spread of B. burgdorferi s.l. and ticks because of their high mobility and shared habitat with important mammalian reservoir hosts. This study aims to better understand the role of avian hosts in tick-borne zoonotic disease transmission cycles in the western United States. We surveyed birds, mammals, and ticks at nine sites in northern California for B. burgdorferi s.l. infection and collected data on other metrics of host community composition such as abundance and diversity of birds, small mammals, lizards, predators, and ticks. We found 22.8% of birds infected with B. burgdorferi s.l. and that the likelihood of avian B. burgdorferi s.l. infection was significantly associated with local host community composition and pathogen prevalence in California. Addition- ally, we found an average tick burden of 0.22 ticks per bird across all species. Predator and lizard abundances were significant predictors of avian tick infestation. These results indicate that birds are relevant hosts in the local B. burgdorferi s.l. transmission cycle in the western United States and quantifying their role in the spread and maintenance of Lyme disease requires further research. 

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