Chytrid fungus (Batrachochytrium dendrobatidis) infection in field and imported amphibian in Taiwan

Batrachochytrium dendrobatidis is the cause of chytridiomycosis, a potentially fatal epidermal infection in amphibian. The fungus infects 2 amphibian orders (Anura and Caudata), 14 families, and at least 250 species. Bull frog (Rana catesbeiana), Xenopus laevis, tadpoles, tiger salamander (Ambystoma tigrinum), and cane toad (Bufo marinus) are known carriers. To determine whether chytridiomycosis has intruded Taiwan, a survey was carried to examine the infecion by histopathology and/or polymerase chain reaction (PCR) in the imported pet frogs, salamanders, meat frogs and field frogs. Retrospectively, a total of 64 frogs and 36 salamanders dying spontaneously and necropsied routinely at Taipei Zoo during the years of 1993 and 2007 were subjected to evaluation. During this period, only one Dendrobates auratus died in December of 2003, which was diagnosed as a mild infection of chytrid fungus histopathologically. For imported pet frogs, a total of 278 frogs were examined by light microscopy, hostopathology and /or PCR, specimens including 14 fresh skin samples, 109 skin swabs, 132 bath water samples and 99 paraffin-embedded skin tissues. Seventeen positive cases were diagnosed, including 4 Ceratophrys sp., 4 Ceratophrys crawelli, 3 Ceratophrys cranwelli, alphosis, 2 Ceratophrys ornate, 2 Phyllomedusa hypochondrialis and 2 Xenopus laveis. Ceratophrys sp. seemed to be the major species affected by chytridiomycosis with a positive rate of 76.4％ (13/17), and the overall positive rates of Ceratophrysl, Xenopus laveis, Phyllomedusa hypochondrialis were 12.9% (13/101), 5.7% (2/35), and 33.3% (2/6), respectively. For meat frogs, a total of 35 fresh skin samples, 35 skin swabs, 36 bath water samples, and 50 paraffin-embedded tissues were collected from 113 frogs. For field frogs, a total of 9 fresh skin sampels, 39 skin swabs, 2 mouthpart swab, 32 bath water samples, and 393 paraffin-embedded tissues were collected from 443 frogs. However, all specimens from meat frogs and field frogs were negative by light microscopy, histopathology and/or PCR. The results of the investigation indicate that chytridiomycosis has indeed been introduced into Taiwan possibly via the importation of pet frogs. Utile now, no evidence of spreading chytridiomycosis to meat frogs and field frogs has been revealed.