Traded animals spread deadly disease to native frogs

30 April 2013

A fungal disease that kills frogs may be spread to endangered frogs in Southeast Asia via commercial trading and releasing of live frogs if immediate conservation measures are not taken. A study by NUS and the Wildlife Conservation Society found the chytrid fungus (Batrachochytrium dendrobatidis) in both native and introduced exotic amphibians sampled in Singapore; it is potentially fatal to rare creatures such as St Andrew's Cross Toad, the Cinnamon Tree Frog and the Malaysian Horned Frog.

The first report to document the disease in Singapore and propose the very real possibility of its spread, the research led by Assistant Professor David Bickford from the NUS Department of Biological Sciences was published in the journal EcoHealth. The scientists believed that the commonly traded American bullfrog could be the vector in the transmission of the disease. The market for amphibians is driven by the sale of frogs as pets, food, bait and traditional medicine.

Assistant Professor Bickford voiced concern that the propagation of the chytrid fungus through commercial trade has serious implications for frogs in Southeast Asia. He said the team discovered animals which tested positive for the disease in local pet shops and in the wild, where buyers released non-native frogs. He said: "This infection could quickly spread to other frogs in Singapore and the region, which would be a huge problem for species which are already under threat."

In the study, samples were collected from 2,389 animals in Laos, Cambodia, Vietnam and Singapore at 51 different sites including farms, locally supplied markets, pet stores and from the wild.

Frogs from Laos and Vietnam tested negative for chytrid, while one in Cambodia came up positive. In Singapore, 13 samples tested positive for chytrid – the first reported for the country. The biologists determined that the fungus was most often detected in the American bullfrog, which is resistant to chytrid infections.

Another cause for concern was that all frogs sampled from 23 frog farms in Vietnam had swelling and inflammation on the skin as well as ulcers and deformed or missing toes associated with bacterial infections. The scientists suspected that frog farms could be a source of infection for the wider environment, as the farmers dumped untreated wastewater directly into natural water channels that can potentially carry infection to other places and animals.

The paper suggested that wider surveys of wild amphibians in Southeast Asia need to be urgently conducted to determine the extent and severity of chytrid fungus and other infectious diseases among a range of species over time. It also recommended research on identifying the chytrid strains endemic to the region and those that may be introduced including through international trade.