When frogs' legs are on the menu, it's not just bad news for their former owners. A new study suggests that the international trade in this delicacy can spread a deadly fungus, which has already driven a number of frog species extinct.
The fungus in question is called Batrachochytrium dendrobatidis, or Bd. First described a decade ago, Bd is spread through water or direct contact between frogs. It infects the skin and penetrates the central nervous system. The disease has already "shattered ecosystems" in some places, notably Central America, says biologist Brian Gratwicke of the Smithsonian Institution's National Zoo in Washington, D.C.
To see how the global frog trade might impact the spread of the disease, Gratwicke and colleagues compiled data from the United Nations Commodity Trade Statistics Database. According to the database, about 10,000 tons of frog legs are shipped around the world each year. The trade is worth roughly $40 million. Although that volume is trivial compared with the annual $42 billion global fish trade, it's risky because of the devastating nature of Bd, the team reported online 19 November in Frontiers in Ecology and the Environment.
Most exported frogs are skinned and frozen, Gratwicke says, thus eliminating the risk of Bd transmission. But, his team notes, products are poorly regulated. For example, frog legs prepared for export are not monitored for pathogens. Gratwicke says that although there has been no proven cases of the Bd pathogen moving to local frogs from frog leg imports, it is possible that spores could get into water systems from unskinned, unfrozen frog legs and thence into local frogs. Another concern is that people who have handled infected frog skins could track it outside. "Even though we have not been able to quantify these risks, given the size and extent of the trade, we feel that these risks need to be managed," says Gratwicke.
Biologist Ian Warkentin of the Memorial University of Newfoundland in Canada says the paper makes it "clearer that this massive, undocumented, and largely unregulated trade in amphibians," including the trade in live animals for pets, is harmful. But Corey Bradshaw, director of the marine biology program at the University of Adelaide, Australia, calls the paper "speculative" and says habitat loss is still the overwhelming threat for the world's frogs. "Disease very much takes the back seat in terms of extinction drivers."