Detection of pathogenic Batrachochytrium dendrobatidis using water filtration, animal and bait testing.

Abstract

The pathogen Batrachochytrium dendrobatidis (Bd) can be challenging to detect at endangered amphibian reintroduction sites. Pre-release Bd detection can be confounded by imperfect animal sampling and the absence of animals. In Study 1, we used historical Bd-positive sites, to concurrently evaluate water filtrates and mouth bar (tadpoles) or skin swab (caudates) samples for Bd using molecular beacon realtime PCR. In Study 2, during a natural outbreak, we used PCR to detect Bd from zoospore-attracting keratin baits (three avian, three snake species). In Study 1, no captured animals (n=116) exhibited clinical signs, although 10.6% were positive, representing three of seven species sampled. In contrast, 5.4% of water filters (n=56) were Bd-positive. In Study 2, after short incubation times, a single duck down feather tested Bd-positive. In conclusion, Bd was detected in asymptomatic amphibians and water filtrate at two sites, and from water only, at two other sites. With continued refinement, semi-quantitative Bd water filtrate screening could better define zoospore-specific disease risk, allowing better characterization of the free-living phase of the organism's life cycle. Finally, these results suggest wild aquatic birds (e.g., waterfowl) should be systematically explored as a means of Bd spread. Since large numbers of aquatic birds migrate, even low Bd transfer rates could be a significant means for disease dissemination.