Emerging wildlife diseases have had severe impacts on host populations. In systems where pathogens have been introduced to naïve host populations, understanding differences in pathogen virulence are important to disentangle mechanisms of host persistence. Following invasion, pathogen evolution is generally balanced between virulence and transmission but can be influenced by numerous factors such as host population structure, variation in host susceptibility, and free-living pathogen survival. Here we examine virulence of the pathogen, Pseudogymnoascus destructans that causes white-nose syndrome, in a North American bat species that has suffered population declines. We experimentally infected 88 Eptesicus fuscus (big brown bats) with P. destructans from enzootic (Eurasia) and epizootic (North America) regions, isolates that span across clades, an isolate from a site in North America where population declines historically occurred and a contemporary isolate collected from the same site 14 years after invasion. Bats were experimentally infected with 5.0 x 106 P. destructans conidia on each wing. Bats were overwintered in environmental chambers for 110 days at 8°C and ~95% RH. To evaluate virulence across isolate treatments, we took epidermal swabs to determine infection intensity (via qPCR) and photographed wing membranes under ultraviolet light to assess P. destructans invasion within wing tissue.
Results/Conclusions
We observed differences in P. destructans infection intensity between contemporary isolates collected from North America and Eurasia. However, we also found that a P. destructans isolate collected during initial pathogen introduction to North America caused higher infections and more tissue invasion than a contemporary isolate from the same site. These findings suggest the slower growth rate and decreased tissue invasion of contemporary isolates may help facilitate recovery of North American bats. Additionally, some international isolates, that have not yet been introduced to North America were also highly virulent to a North American host species, which would support the need for surveillance and prevention of additional introductions in the future.
