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USGS2025

Differential population responses to white-nose syndrome between two Michigan bat hibernacula are not due to differences in host susceptibility

Disease outcomes result from the interaction between host, pathogen, and environmental factors. Understanding how these components interact to influence spatial and temporal variations in disease severity can enhance our insights into the drivers of disease outbreaks, ultimately improving our ability to mitigate the impact of disease through better forecasts and management actions. White-nose syndrome (WNS) in bats, caused by the fungal pathogen Pseudogymnoascus destructans (Pd), has been detected in hibernating bats across much of the United States and Canada. This pathogen has led to widespread population declines in some bat species, for example, Myotis lucifugus ; however, not all infected populations exhibit similar decreases in numbers. Despite long-term detection and high infection levels, the population of M. lucifugus that uses Tippy Dam, in northern Michigan, as a hibernaculum has not experienced a decline compared to other populations in the state. To assess local population effects that may contribute to reduced disease severity at Tippy Dam, we brought 30 hibernating M. lucifugus from Tippy Dam and 30 from a geographically similar hibernaculum with a history of declines from WNS into captivity at the U.S. Geological Survey, National Wildlife Health Center. We challenged the bats with a Pd inoculum and monitored survival, pathology, and Pd loads for up to 120 days. This allowed us to remove local environmental effects that could influence WNS disease severity. We observed no effect of source population on either survival or wing damage from Pd infection. Our results suggest that population persistence and lowered disease severity in Tippy Dam are likely driven by local environmental factors found within the dam. As Pd continues to spread westward, understanding environmental factors that influence the severity of Pd infection in hibernating bats has the potential to guide management decisions and help predict the survival of susceptible bat species in the western United States.

Michigan↗

USGS2012

Frequent arousal from hibernation linked to severity of infection and mortality in bats with white-nose syndrome

White-nose syndrome (WNS), an emerging infectious disease that has killed over 5.5 million hibernating bats, is named for the causative agent, a white fungus (Geomyces destructans (Gd)) that invades the skin of torpid bats. During hibernation, arousals to warm (euthermic) body temperatures are normal but deplete fat stores. Temperature-sensitive dataloggers were attached to the backs of 504 free-ranging little brown bats (Myotis lucifugus) in hibernacula located throughout the northeastern USA. Dataloggers were retrieved at the end of the hibernation season and complete profiles of skin temperature data were available from 83 bats, which were categorized as: (1) unaffected, (2) WNS-affected but alive at time of datalogger removal, or (3) WNS-affected but found dead at time of datalogger removal. Histological confirmation of WNS severity (as indexed by degree of fungal infection) as well as confirmation of presence/absence of DNA from Gd by PCR was determined for 26 animals. We demonstrated that WNS-affected bats aroused to euthermic body temperatures more frequently than unaffected bats, likely contributing to subsequent mortality. Within the subset of WNS-affected bats that were found dead at the time of datalogger removal, the number of arousal bouts since datalogger attachment significantly predicted date of death. Additionally, the severity of cutaneous Gd infection correlated with the number of arousal episodes from torpor during hibernation. Thus, increased frequency of arousal from torpor likely contributes to WNS-associated mortality, but the question of how Gd infection induces increased arousals remains unanswered.

Michigan, Pennsylvania, Vermont, West Virginia↗