Distribution of the amphibian chytrid Batrachochytrium dendrobatidis and keratin during tadpole development

A large outbreak of chytridiomycosis occurred in captive metamorphs of Mixophyes fasciolatus that died between 9 and 25 days post metamorphosis. The mortality rate in infected tubs was 100% and more than 500 frogs died. Examination of the husbandry records suggested that tadpoles had been infected before two weeks of age. However, a sample of tadpoles separated before hatching remained uninfected. We studied the changes in distribution of keratin and sporangia of Batrachochytrium dendrobatidis in tadpoles during development, by examination of histology sections stained with Ayoub-Shklar stain. Keratin occurred only on the mouthparts during most of tadpole life, and appeared onthe feet shortly before metamorphosis. At metamorphosis the keratinized mouthparts are shed before keratin forms on the skin of the body, B. dendrobatidis only occurred on keratinized, stratified epidermis and followed the changes in distribution. There is a rapid redistribution of B. dendrobatidis at metamorphosis leading to fatal infection in M. fasciolatus. These findings are useful considerations when translocating tadpoles as well as for diagnosis and treatment.