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1. Estimating pathogen‐spillover risk using host–ectoparasite interactions

   https://doi.org/10.1002/ece3.11509  

   Brennan, Reilly N; Paulson, Sally L; Escobar, Luis E (June 2024, Ecology and Evolution)

   Abstract Pathogen spillover corresponds to the transmission of a pathogen or parasite from an original host species to a novel host species, preluding disease emergence. Understanding the interacting factors that lead to pathogen transmission in a zoonotic cycle could help identify novel hosts of pathogens and the patterns that lead to disease emergence. We hypothesize that ecological and biogeographic factors drive host encounters, infection susceptibility, and cross‐species spillover transmission. Using a rodent–ectoparasite system in the Neotropics, with shared ectoparasite associations as a proxy for ecological interaction between rodent species, we assessed relationships between rodents using geographic range, phylogenetic relatedness, and ectoparasite associations to determine the roles of generalist and specialist hosts in the transmission cycle of hantavirus. A total of 50 rodent species were ranked on their centrality in a network model based on ectoparasites sharing. Geographic proximity and phylogenetic relatedness were predictors for rodents to share ectoparasite species and were associated with shorter network path distance between rodents through shared ectoparasites. The rodent–ectoparasite network model successfully predicted independent data of seven known hantavirus hosts. The model predicted five novel rodent species as potential, unrecognized hantavirus hosts in South America. Findings suggest that ectoparasite data, geographic range, and phylogenetic relatedness of wildlife species could help predict novel hosts susceptible to infection and possible transmission of zoonotic pathogens. Hantavirus is a high‐consequence zoonotic pathogen with documented animal‐to‐animal, animal‐to‐human, and human‐to‐human transmission. Predictions of new rodent hosts can guide active epidemiological surveillance in specific areas and wildlife species to mitigate hantavirus spillover transmission risk from rodents to humans. This study supports the idea that ectoparasite relationships among rodents are a proxy of host species interactions and can inform transmission cycles of diverse pathogens circulating in wildlife disease systems, including wildlife viruses with epidemic potential, such as hantavirus. 

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2. Environmental reservoir dynamics predict global infection patterns and population impacts for the fungal disease white-nose syndrome

   https://doi.org/10.1073/pnas.1914794117  

   Hoyt, Joseph R.; Langwig, Kate E.; Sun, Keping; Parise, Katy L.; Li, Aoqiang; Wang, Yujuan; Huang, Xiaobin; Worledge, Lisa; Miller, Helen; White, J. Paul; et al (March 2020, Proceedings of the National Academy of Sciences)

   Disease outbreaks and pathogen introductions can have significant effects on host populations, and the ability of pathogens to persist in the environment can exacerbate disease impacts by fueling sustained transmission, seasonal epidemics, and repeated spillover events. While theory suggests that the presence of an environmental reservoir increases the risk of host declines and threat of extinction, the influence of reservoir dynamics on transmission and population impacts remains poorly described. Here we show that the extent of the environmental reservoir explains broad patterns of host infection and the severity of disease impacts of a virulent pathogen. We examined reservoir and host infection dynamics and the resulting impacts of Pseudogymnoascus destructans , the fungal pathogen that causes white-nose syndrome, in 39 species of bats at 101 sites across the globe. Lower levels of pathogen in the environment consistently corresponded to delayed infection of hosts, fewer and less severe infections, and reduced population impacts. In contrast, an extensive and persistent environmental reservoir led to early and widespread infections and severe population declines. These results suggest that continental differences in the persistence or decay of P. destructans in the environment altered infection patterns in bats and influenced whether host populations were stable or experienced severe declines from this disease. Quantifying the impact of the environmental reservoir on disease dynamics can provide specific targets for reducing pathogen levels in the environment to prevent or control future epidemics. 

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3. Prior heat waves improve survival of field but not domesticated populations of tobacco hornworm exposed to repeated bacterial infections

   https://doi.org/10.1111/1365-2435.70001  

   Malinski, Katherine H; Willett, Christopher S; Kingsolver, Joel G (March 2025, Functional Ecology)

   Abstract In insects and other invertebrates, prior pathogen exposures can improve immune responses and survival to subsequent infections through immune priming. Alternatively, stress and metabolic costs of multiple infections can impair host immunity and survival. The effects of high‐temperature extremes on host–pathogen interactions are not well understood despite the increasing occurrence of heat waves caused by climate change.The response of insects to heat waves and pathogens depends on recent evolutionary history with selective pressures. Domestication of insect pests has occurred in lab colonies of model species, reducing selective pressures for immune and heat stress responses. Lab strains are often used in immunological or heat stress experiments to represent wild field strains, but the efficacy of this approach is seldom evaluated.Using the tobacco hornworm (Manduca sexta), we tested the impact of a heat wave during initial pathogen exposure on survival of a secondary infection withBacillus thuringiensisbacteria. We used a domesticated lab population and a naturally occurring field population ofM. sextato evaluate the impacts of recent domestication on immune and thermal responses.A heat wave during initial infection significantly increased survival of the secondaryB. thuringiensisinfection in the field, but not the lab population ofM. sexta.In the field population, survival of the repeated infection was temperature dependent: exposure to an initial infection event reduced survival of the secondary infection at the control temperature regime, consistent with a stress effect. However, a heat wave during the initial infection event increased survival of the secondary infection, consistent with immune priming effects.The results of this study demonstrate that (a) insect response to thermal stress and pathogens can depend on recent domestication and (b) responses of hosts to repeat pathogen exposures can be temperature‐dependent, suggesting that cross‐talk between the heat stress and immune memory pathways may have important consequences for host–pathogen outcomes under heat wave events. Read the freePlain Language Summaryfor this article on the Journal blog. 

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4. Many roads to reservoirs? How susceptibility and shedding shape host competence in amphibians

   https://doi.org/10.1111/1365-2435.70250  

   DeMarchi, Joseph A; Carter, Edward D; Gray, Matthew J; Lutz, Kurt R; Schrock, Sarah_A R; Searle, Catherine L; Wallace, Cassidy L; Wilber, Mark Q (March 2026, Functional Ecology)

   Abstract Host competence—the ability to acquire, harbour and transmit infections—drives pathogen spread and persistence in multi‐host communities. Evaluating species‐specific competence is critical for predicting transmission, particularly for generalist fungal pathogens likeBatrachochytrium dendrobatidis(Bd). Despite its central role in disease dynamics, we lack an epidemiologically grounded competence metric that rigorously accounts for how infection intensity affects a host's competence. This knowledge gap limits our ability to compare mechanisms across species and assess their roles in pathogen persistence. To address these challenges, we developed a novel, load‐dependent competence metric using host–pathogen Integral Projection Models (IPMs) that integrates variation in susceptibility, within‐host pathogen growth and pathogen shedding dynamics.We applied this metric to laboratory‐based challenge experiments with three common North American amphibians (Notophthalmus viridescens,Rana clamitansandRana catesbeianus) that persist endemically with Bd. Using dose–response assays and repeated pathogen shedding measurements across species, we asked: (i) is there a consistent, non‐linear relationship between infection intensity and pathogen shedding across species? and (ii) which load‐based traits best predict host competence? We quantified four of five components of host competence—susceptibility, pathogen growth, pathogen survival and load‐dependent shedding—and used these to parameterize species‐specific IPMs, integrating competence into a single relative metric across species.We found that Bd shedding increased non‐linearly with infection intensity, contradicting the standard assumption that Bd shedding is linearly related to infection intensity.Notophthalmus viridescensandR. catesbeianuswere the most competent hosts but through distinct pathways: high susceptibility inN. viridescensand elevated shedding rates inR. catesbeianus. In contrast, density‐dependent reductions in pathogen growth and shedding limitedR. clamitanscompetence. Thus, species‐level competence is not determined by a single trait, but emerges from interactions among multiple load‐based processes.Our results demonstrate that variation in competence emerges from distinct, species‐specific processes across multiple dimensions of competence. By linking individual infection dynamics to population‐level transmission potential, our integrative framework provides a more mechanistic approach to predicting host contributions to community‐level pathogen persistence. Read the freePlain Language Summaryfor this article on the Journal blog. 

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5. ‘Disease‐smart’ outcrossing can enhance individual fitness and increase survival via immune priming against pathogens: New approaches to strengthen genetic rescue efforts

   https://doi.org/10.1111/icad.12842  

   Ghosh, Enakshi; Wallace, Matthew; Hufbauer, Ruth A (September 2025, Insect Conservation and Diversity)

   Abstract We studied the potential of combining insect immune priming with the introduction of diverse migrants to safeguard individuals from an inbred population from disease as a technique for enhancing genetic rescue efforts.Immune priming in insects refers to the stronger immune response insects have against pathogens following exposure. This enhanced immunity can be passed on to offspring and holds promise for insect conservation efforts against diseases.We compared the fitness benefits to individuals from a small, inbred population of two treatments: the addition of genetically diverse migrants that had not been primed and the addition of immune‐primed migrants. While both types of migrants enhanced reproduction, as in cases of genetic rescue, only primed migrants led to improved survival on exposure to a pathogen.Better immunity led to a trade‐off with reproduction in immune‐primed migrants, but this was not evident upon outcrossing with the target individuals, revealing synergies between hybrid vigour and immune priming.Given the demographic constraints and stochasticity that can exacerbate the effects of disease outbreaks in small populations, our results serve as a proof of concept for combining immune priming with assisted migration, which offers a proactive strategy to mitigate disease impacts while enhancing genetic diversity. 

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