Overview of Batrachochytrium and frog declines

Lee Berger^1,2, Rick Speare², Alex Hyatt¹ and Gerry Marantelli³

¹ CSIRO Australian Animal Health Laboratory, Geelong, Victoria, Australia.
² School of Public Health and Tropical Medicine, James Cook University, Townsville, Queensland, Australia
³ Amphibian Research Centre, P.O. Box 424, Brunswick, Victoria, Australia 3056.
Email: lee.berger@dah.csiro.au

The pattern of many declines in Australian frogs is consistent with being caused by epidemic deaths after the suspected introduction of Batrachochytrium into numerous protected habitats after 1978. As sudden declines occurred in stream dwelling frogs while tadpoles survived, Batrachochytrium is a likely cause as it is waterborne and does not kill tadpoles. Tadpoles can potentially carry infections in their mouthparts from soon after hatching until metamorphic climax when the beaks are shed and sporangia are rapidly redistributed to the skin of the body. Exposure of great barred frogs (Mixophyes fasciolatus) to cultured fungal zoospores or infected skin samples resulted in 100% mortality with doses down to 100 zoospores. Frogs died between 10 and 47 days post exposure. The fungal sporangia grow within cells in the superficial layers of the skin that results in thickening of the epidermis and the keratin layer. Batrachochytrium is now widespread in Australian frogs and has so far been found in 43 native Myobatrachid and Hylid species, as well as cane-toads and axolotyls. Infected frogs have been found in all states but not the Northern Territory. In Queensland and NSW 71% of ill frogs examined from 1993 to the present were collected between July and October. We are continuing to find new host and location records. Current diagnostic tests rely on microscopy, but polyclonal and monoclonal antibodies have been produced for use in simple field and laboratory tests.