COS 61-5 - Winter is coming: Temperature dependent virulence of Batrachochytrium salamandrivorans

Wednesday, August 14, 2019: 2:50 PM
L011/012, Kentucky International Convention Center
E. Davis Carter1, Debra L. Miller1,2, Brittany A. Bajo1, Markese L. Bohanon1, Anna C Peterson1, Kurt T. Ash1, Pattarawan Watcharaanantapong1 and Matthew J. Gray1, (1)Center for Wildlife Health, University of Tennessee, Knoxville, TN, (2)Department of Biomedical and Diagnostic Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN
Background/Question/Methods

Batrachochytrium salamandrivorans (Bsal) is a recently emergent fungal pathogen that has caused dramatic population declines of European fire salamanders (Salamandra salamandra). Initial in vitro growth experiments suggested that Bsal has an optimum growth temperature between 10 – 15 C and an upper thermal limit of 25 C. However, field studies in Vietnam, an area where Bsal is suspected to be endemic, detected the pathogen on amphibian skin swabs from animals inhabiting aquatic systems with average temperatures between 20 – 25 C and reaching as high as 26.4 C. The average temperature in northern Europe where Bsal was first detected emerging is 18 C during summer and 3 C during winter. Preliminary risk analyses suggest that temperature will be an important factor driving Bsal invasion in the United States if the pathogen is introduced. To evaluate this hypothesis, we exposed adult eastern newts (Notophthalmus viridescens) – a salamander species found throughout eastern North America – to a sham inoculation of autoclaved water (control) or one of four Bsal zoospore doses (5 x 10e3-6) at one of three ambient temperatures, 6 C, 14 C or 22 C. Survival and infection prevalence were recorded for 90 days post-exposure to the pathogen.

Results/Conclusions

At 14 C, all eastern newts became infected and died within one month post-exposure to Bsal. Median survival duration at 14 C was 26, 20, 14 and 7 days for 5x10e3, 5x10e4, 5x10e5 and 5x10e6, respectively. In contrast, no individuals became infected or died when exposed to Bsal at 22 C. At 6 C, results were intermediate, with survival durations approximately one week longer than 14 C. However, newts that died from Bsal chytridiomycosis at 6 C had lower zoospore loads than at 14 C, suggesting lower infection tolerance at lower temperature. Thus, slower Bsal growth on salamanders may occur at colder temperatures, but mortality occurs at a lower zoospore threshold, perhaps due to negative influences of temperature on host immune responses or microbiome. Collectively, our results suggest that Bsal invasion probability in the United States may be geographically narrower than indicated in previous risk models, with greatest likelihood of emergence occurring at mid- to northern latitudes and at higher elevations, often where salamander diversity is the greatest. Seasonal fluctuations in disease emergence also are expected, with autumn and winter months experiencing greatest mortality – the White Walker Effect. Future experiments are planned at finer temperature gradients, while allowing diel fluctuations.