Amphibian developmental response to a natural anti-fungal treatment for the bat White-nose syndrome

Background/Question/Methods White-Nose Syndrome is an emerging bat epidemic that, with its current spread, is rapidly turning into a wildlife crisis.  Outside of limiting cave access, wildlife managers have few methods of control of this fungal infection.  The fungus in question is Geomyces destructans. Our study investigates the environmental impact of a naturally occurring, plant produced, volatile organic compound (Carvone) that is currently undergoing testing as an antifungal agent to treat White-Nose Syndrome in bats. Carvone is a derivative of spearmint oil and this investigation focuses on the potential toxicity of this anti-fungal agent on other cave aquatic organisms, namely amphibians.  In testing Carvone, we conducted Frog Embryo Teratogenesis Assays with tadpoles of the frog Xenopus laevis (FETAX).  This FETAX protocol provides a standardized method for evaluating potentially hazardous materials on the development of vertebrates.  Mortality and developmental abnormalities were recorded in these replicates through the 96 hour stage of development followng the FETAX protocols.

Results/Conclusions After running a range finding series of Carvone test concentrations followed by a set of test series of Carvone concentrations, we were able to find a sequence of lethal concentrations of this fungicide. The LC₅₀ for Carvone tested on X. laevis was 10.1 ppm based on a Probit analysis. An optimal solution was determined after 10 iterations,  with Z = 11.203, P < 0.001. The 5% mortality level of X. laevis was determined to be 4.0 ppb. Tests are currently being made to determine if this lower concentration of Carvone is sufficient to retard or eliminate the G. destructans growth. By determining if antifungal compounds like Carvone can limited impact on sentinel species like X. laevis, we can continue tests on more sensitive cave species.