Efficacy of Visual Surveys for White-Nose Syndrome at Bat Hibernacula

Abstract

White-Nose Syndrome (WNS) is an epizootic disease in hibernating bats caused by the fungus Pseudogymnoascus destructans. Surveillance for P. destructans at bat hibernacula consists primarily of visual surveys of bats, collection of potentially infected bats, and submission of these bats for laboratory testing. Cryptic infections (bats that are infected but display no visual signs of fungus) could lead to the mischaracterization of the infection status of a site and the inadvertent spread of P. destructans. We determined the efficacy of visual detection of P. destructans by examining visual signs and molecular detection of P. destructans on 928 bats of six species at 27 sites during surveys conducted from January through March in 2012–2014 in the southeastern USA on the leading edge of the disease invasion. Cryptic infections were widespread with 77% of bats that tested positive by qPCR showing no visible signs of infection. The probability of exhibiting visual signs of infection increased with sampling date and pathogen load, the latter of which was substantially higher in three species (Myotis lucifugus, M. septentrionalis, and Perimyotis subflavus). In addition, M. lucifugus was more likely to show visual signs of infection than other species given the same pathogen load. Nearly all infections were cryptic in three species (Eptesicus fuscus, M. grisescens, and M. sodalis), which had much lower fungal loads. The presence of M. lucifugus or M. septentrionalis at a site increased the probability that P. destructans was visually detected on bats. Our results suggest that cryptic infections of P. destructans are common in all bat species, and visible infections rarely occur in some species. However, due to very high infection prevalence and loads in some species, we estimate that visual surveys examining at least 17 individuals of M. lucifugus and M. septentrionalis, or 29 individuals of P. subflavus are still effective to determine whether a site has bats infected with P. destructans. In addition, because the probability of visually detecting the fungus was higher later in winter, surveys should be done as close to the end of the hibernation period as possible.

Determinants of Pseudogymnoascus destructans within bat hibernacula: Implications for surveillance and management of white‐nose syndrome

“…Environmental substrates (sediment or wall surfaces) were sampled for Pd at each data‐logger location within each hibernaculum three times per year in summer (August), early hibernation (November/December) and late hibernation (March) to coincide with the hibernation phenology of bats and seasonal dynamics of WNS (Janicki et al., ; Langwig, Frick, et al., ; Norquay & Willis, ). March sampling trips were delayed at NY1 to May 2013 and at NY2 to June 2013 and 2014 because of ice obstructing site entrances.…”

“…For environmental substrates, we hypothesized that presence–absence and abundance of Pd would be correlated with location in a hibernaculum (Vanderwolf, Malloch, McAlpine, & Forbes, ), time since first detection of WNS at the site (Langwig, Hoyt, et al., ), time of year (Langwig, Frick, et al., ) and temperature at the sampling location (Verant, Boyles, Waldrep, Wibbelt, & Blehert, ). Additionally, we hypothesized that Pd on bats would correlate with species and temperature (Langwig et al., ), sex (Grieneisen, Brownlee‐Bouboulis, Johnson, & Reeder, ), body condition and visual evidence of WNS (Janicki et al., ; Turner et al., ). We tested these hypotheses using a multi‐step modelling approach applied to six hibernacula at different stages of WNS, from first introduction of Pd to establishment of WNS within a bat population undergoing severe declines.…”

Detecting viable Pseudogymnoascus destructans (Ascomycota: Pseudeurotiaceae) from walls

“…Pd was initially detected at sites by assessing live hibernating bats for the presence of characteristic Pd fungal growth. However, lack of visible Pd growth does not equate to its absence (Janicki et al 2015), so visual assessments of Pd presence on bats may underestimate arrival date.…”

“…The ability to detect Pd within a hibernaculum is an important part of disease surveillance. Detection often relies on the observation of visible fungal growth and behavioral changes in hibernating bats, but Pd can arrive before such changes are noticeable (Janicki et al, 2015). Pd surveillance is often conducted with culture-independent methods of molecular genetics, but such approaches cannot discriminate between viable and nonviable fungus.…”

Molecular Detection ofPseudogymnoascus destructans(Ascomycota: Pseudeurotiaceae) and Unidentified Fungal Dermatitides on Big Brown Bats (Eptesicus fuscus) Overwintering inside Buildings in Canada

“…As winter approaches some migratory bats leave the northern portion of their range, possibly avoiding the need for torpor. Although WNS is reported in caveroosting big brown bats (Eptesicus fuscus) and Pd prevalence on this species can be high (Langwig et al 2014 Janicki et al 2015). The affected individuals also lacked grossly visible or microscopic lesions consistent with WNS (Meteyer et al 2009), providing further evidence of the cryptic nature of these preclinical or subclinical infections.…”