'Fatal phaeohyphomycosis due to Exophiala sp. infection in a free-living common toad (Bufo bufo)

A wild adult female common toad (Bufo bufo) found dead in Scotland, Great Britain, in September 2016, was found to have hepatomegaly, a large soft tissue mass in the coelomic cavity (2.7g, 3.5 x 2.3 x 1.8 cm), and numerous dark-red papules (1-2 mm diameter) in the skin and subjacent tissue over the back and dorsal aspects of the limbs. Histopathological examination identified marked hepatitis and coelomitis associated with pigmented fungal hyphae; results consistent with a diagnosis of phaeohyphomycosis. Sequencing of the internal transcribed spacer region and the D1-D2 region of the large subunit of the ribosomal RNA gene from affected liver tissue identified the presence of Exophiala (Chaetothyriales) sp., a black yeast previously identified as a cause of amphibian phaeohyphomycosis. To the authors’ knowledge, this is the first published report of Exophiala sp. in a wild or captive amphibian in Europe and the first description of phaeohyphomycosis affecting a free-living amphibian in Great Britain. Exophiala spp. are saprobes and opportunistic pathogens. It has been postulated that phaeohyphomycosis is a disease of immunocompromised amphibians. However, we found no evidence of significant concurrent infection or generalised debility in this common toad. Phaeohyphomycosis appears to be a sporadic cause of mortality in amphibians and this report adds to the growing list of pathogens known to affect wild amphibians in Europe