Developing a safe antifungal treatment protocol to eliminate Batrachochytrium dendrobatidis from amphibians.

ABSTRACT

Batrachochytrium dendrobatidis is one of the most pathogenic microorganisms affecting amphibians in both captivity and in nature. The establishment of B. dendrobatidis free, stable, amphibian captive breeding colonies is one of the emergency measures that is being taken to save threatened amphibian species from extinction. For this purpose, in vitro antifungal susceptibility testing and the development of efficient and safe treatment protocols are required. In this study, we evaluated the use of amphotericin B and voriconazole to treat chytridiomycosis in amphibians. The concentration at which the growth of five tested B. dendrobatidis strains was inhibited was 0.8 µg/ml for amphotericin B and 0.0125 µg/ml for voriconazole. To completely eliminate a mixture of sporangia and zoospores of strain IA042 required 48 h of exposure to 8 µg/ml of amphotericin B or 10 days to 1.25 µg/ml of voriconazole. Zoospores were killed within 0.5 h by 0.8 µg/ml of amphotericin B, but even after 24 h exposure to 1.25 µg/ml of voriconazole they remained viable. Amphotericin B was acutely toxic for Alytes muletensis tadpoles at 8 µg/ml, whereas toxic side effects were not noticed during a seven-day exposure to voriconazole at concentrations as high as 12.5 µg/ml. The voriconazole concentrations remained stable in water during this exposure period. On the basis of this data, experimentally inoculated postmetamorphic Alytes cisternasii were sprayed once daily for 7 days with a 1.25 µg/ml solution of voriconazole in water which eliminated the B. dendrobatidis infection from all treated animals. Finally, treatment of a naturally infected colony of poison dart frogs (Dendrobatidae) using this protocol, combined with environmental disinfection, cleared the infection from the colony.