More Like this

1. Host abundance and heterogeneity in infectiousness determine extent of the environmental reservoir

   Nichole A. Laggan, Katy L. (January 2022, bioRxiv)

   Environmental pathogen reservoirs exist for many globally important diseases and can fuel disease outbreaks, affect pathogen evolution, and increase the threat of host extinction. Differences in pathogen shedding among hosts can create mosaics of infection risk across landscapes by increasing pathogen contamination in high use areas. However, how the environmental reservoir establishes in multi-host communities and the importance of factors like host-specific infection and abundance in environmental contamination and transmission remain important outstanding questions. Here we examine how Pseudogymnoascus destructans, the fungal pathogen that causes white-nose syndrome in bats, invades and establishes in the environment. We quantified dynamic changes in pathogen shedding, infection intensities, host abundance, and the subsequent propagule pressure imposed by each species within the community. We find that the initial establishment of the pathogen reservoir is driven by different species within the community than those that are responsible for maintaining the reservoir over time. Our results also show that highly shedding species do not always contribute the most to pathogen reservoirs. More broadly, we demonstrate how individual host shedding rates scale to influence landscape-level pathogen contamination. 

   more » « less
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. 

   more » « less
3. Wildfire alters the disturbance impacts of an emerging forest disease via changes to host occurrence and demographic structure

   https://doi.org/10.1111/1365-2745.13495  

   Simler‐Williamson, Allison B.; Metz, Margaret R.; Frangioso, Kerri M.; Rizzo, David M.; Thrall, ed., Peter (September 2020, Journal of Ecology)

   Abstract Anthropogenic activities have altered historical disturbance regimes, and understanding the mechanisms by which these shifting perturbations interact is essential to predicting where they may erode ecosystem resilience. Emerging infectious plant diseases, caused by human translocation of nonnative pathogens, can generate ecologically damaging forms of novel biotic disturbance. Further, abiotic disturbances, such as wildfire, may influence the severity and extent of disease‐related perturbations via their effects on the occurrence of hosts, pathogens and microclimates; however, these interactions have rarely been examined.The disease ‘sudden oak death’ (SOD), associated with the introduced pathogenPhytophthora ramorum, causes acute, landscape‐scale tree mortality in California's fire‐prone coastal forests. Here, we examined interactions between wildfire and the biotic disturbance impacts of this emerging infectious disease. Leveraging long‐term datasets that describe wildfire occurrence andP. ramorumdynamics across the Big Sur region, we modelled the influence of recent and historical fires on epidemiological parameters, including pathogen presence, infestation intensity, reinvasion, and host mortality.Past wildfire altered disease dynamics and reduced SOD‐related mortality, indicating a negative interaction between these abiotic and biotic disturbances. Frequently burned forests were less likely to be invaded byP. ramorum, had lower incidence of host infection, and exhibited decreased disease‐related biotic disturbance, which was associated with reduced occurrence and density of epidemiologically significant hosts. Following a recent wildfire, survival of mature bay laurel, a key sporulating host, was the primary driver ofP. ramoruminfestation and reinvasion, but younger, rapidly regenerating host vegetation capable of sporulation did not measurably influence disease dynamics. Notably, the effect ofP. ramoruminfection on host mortality was reduced in recently burned areas, indicating that the loss of tall, mature host canopies may temporarily dampen pathogen transmission and ‘release’ susceptible species from significant inoculum pressure.Synthesis. Cumulatively, our findings indicate that fire history has contributed to heterogeneous patterns of biotic disturbance and disease‐related decline across this landscape, via changes to the both the occurrence of available hosts and the demography of epidemiologically important host populations. These results highlight that human‐altered abiotic disturbances may play a foundational role in structuring infectious disease dynamics, contributing to future outbreak emergence and driving biotic disturbance regimes. 

   more » « less
4. The importance of peripheral populations in the face of novel environmental change

   https://doi.org/10.1098/rspb.2024.2331  

   Hoff, Samantha; Hoyt, Joseph R; Langwig, Kate E; Johnson, Luanne; Olson, Elizabeth; O’Dell, Danielle; Pendergast, Casey J; Herzog, Carl J; Parise, Katy L; Foster, Jeffrey T; et al (January 2025, Proceedings of the Royal Society B: Biological Sciences)

   Anthropogenically driven environmental change has imposed substantial threats on biodiversity, including the emergence of infectious diseases that have resulted in declines of wildlife globally. In response to pathogen invasion, maintaining diversity within host populations across heterogenous environments is essential to facilitating species persistence. White-nose syndrome is an emerging fungal pathogen that has caused mass mortalities of hibernating bats across North America. However, in the northeast, peripheral island populations of the endangered northern myotis (Myotis septentrionalis) appear to be persisting despite infection while mainland populations in the core of the species range have experienced sharp declines. Thus, this study investigated host and environmental factors that may contribute to divergent population responses. We compared patterns of pathogen exposure and infection intensity between populations and documented the environmental conditions and host activity patterns that may promote survival despite disease invasion. For island populations, we found lower prevalence and less severe infections, possibly due to a shorter hibernation duration compared to the mainland, which may reduce the time for disease progression. The coastal region of the northern myotis range may serve as habitat refugia that enables this species to persist despite pathogen exposure; however, conservation efforts could be critical to supporting species survival in the long term. 

   more » « less
5. Putative resistance and tolerance mechanisms have little impact on disease progression for an emerging salamander pathogen

   https://doi.org/10.1111/1365-2435.13754  

   Wilber, Mark Q.; Carter, Edward Davis; Gray, Matthew J.; Briggs, Cheryl J.; Pedersen, ed., Amy (January 2021, Functional Ecology)

   Abstract Resistance and tolerance are unique host defence strategies that can limit the impacts of a pathogen on a host. However, for most wildlife–pathogen systems, there are still fundamental uncertainties regarding (a) how changes in resistance and tolerance can affect disease outcomes and (b) the mechanisms underlying resistance and tolerance in host populations.Here, we first compared observed patterns of resistance and tolerance and their effects on disease outcomes among salamander species that are susceptible to infection and mortality from the emerging fungal pathogenBatrachochytrium salamandrivorans(Bsal). We then tested whether two putative mechanisms that contribute to host resistance and tolerance, skin sloughing and skin lesion reduction, predicted reducedBsalgrowth rate or increased host survival during infection, respectively.We performed multi‐doseBsalchallenge experiments on four species of Salamandridae found throughout North America. We combined the laboratory experiments with dynamic models and sensitivity analysis to examine how changes in load‐dependent resistance and tolerance functions affectedBsal‐induced mortality risk. Finally, we used our disease model to test whether skin sloughing and lesion reduction predicted variability in infection outcomes not described byBsalinfection intensity.We found that resistance and tolerance differed significantly among salamander species, with the most susceptible species being both less resistance and less tolerant ofBsalinfection. Our dynamic model showed that the relative influence of resistance versus tolerance on host survival was species‐dependent—increasing resistance was only more influential than increasing tolerance for the least tolerant species where changes in pathogen load had a threshold‐like effect on host survival. Testing two candidate mechanisms of resistance and tolerance, skin sloughing and lesion reduction, respectively, we found limited support that either of these processes were strong mechanisms of host defence.Our study contributes to a broader understanding of resistance and tolerance in host–pathogen systems by showing that differences in host tolerance can significantly affect whether changes in resistance or tolerance have larger effects on disease outcomes, highlighting the need for species and even population‐specific management approaches that target host defence strategies. A freePlain Language Summarycan be found within the Supporting Information of this article. 

   more » « less