Nov
20

Global trade in frog legs may be spreading deadly disease

Frog legs are a delicacy in many cuisines and most countries participate in the $40-million-per-year culinary trade of frogs in some way, with 75 percent of frog legs consumed in France, Belgium and the United States. However, Smithsonian scientists and colleagues have found that this trade may be helping to spread a pathogen that is deadly to amphibians around the world.
Amphibians are rapidly declining worldwide. More than one-third of the nearly 6,000 amphibian species are threatened with extinction—primarily because of disease. Among the known amphibian pathogens, the parasitic fungus Batrachochytrium dendrobatidis, also known as amphibian chytrid (KI-trid), is a top concern. The fungus, which attacks keratin proteins in the skin of amphibians, including frogs, causes respiratory and neurological damage and eventually death.

The American bullfrog is one of many species used in the international  frog leg trade. (Photo by Mehgan Murphy)

The American bullfrog is one of many species used in the international frog leg trade. (Photo by Mehgan Murphy)

“Amphibian chytrid is an unusual example of a disease that is a primary cause of extinction in amphibian species,” Brian Gratwicke, biologist at the National Zoo and lead author of the team’s paper, explains. “In fact, amphibian chytrid has been listed as a likely threat in 94 cases out of the 159 extinct and potentially extinct amphibian species. There are several hypotheses about how amphibian chytrid has spread around the world, but the trade in amphibians for food, bait, pets and laboratory animals has been identified as the most likely mode of spread.”

The scientists’ research focused on the decade between 1996 through 2006, during which more than 100,000 metric tons of frog legs—approximately 100 to 400 million individual animals—were imported from both wild and farmed sources, at a net value approaching half a billion dollars. One kilogram of frog legs, requiring 10 to 40 frogs averaged about $4 over this period.

The scientists found no recorded cases of the extinction of a frog species caused by collection for food. However, given the growing importance of aquaculture to supply frog legs to global markets, the team stresses that the risk of disease spread through poorly regulated amphibian trade is probably an even greater risk to amphibian biodiversity than the direct population effects of overharvesting.

Frog legs for sale at an Indonesian market (Photo by A. Roselli)

Frog legs for sale at an Indonesian market (Photo by A. Roselli)

In countries such as Indonesia, which exports about 45 percent of all frog legs, the majority of animals are thought to be wild-caught and there is little to no effort to monitor this food source for disease pathogens. “Any trade in live frogs or fresh, un-skinned frog legs presents a substantial risk of the spread of amphibian chytrid,” Gratwicke says. “The implementation and enforcement of some key amphibian trade policies could be a cost-effective conservation tool to mitigate disease risks associated with the trade.”

The exact origin of amphibian chytrid is unknown, but one theory is that it originated in Southern Africa and was distributed worldwide in the 1950s through the trade of the African clawed frog for use in pregnancy-testing. Amphibian chytrid has been detected in many parts of the United States, but some species are apparently resistant to the fungus, and it is not always associated with amphibian declines. The most dramatic declines have been observed in mountainous parts of Central and South America and Australia where it is responsible for the disappearance and probable extinction of many species.

The team’s findings are published in the scientific journal Frontiers in Ecology and the Environment.

Global exporters and importers of frog legs (1996 – 2006). (Data from the United Nations Commodity Trade Statistics Database)

Global exporters and importers of frog legs (1996 – 2006). (Data from the United Nations Commodity Trade Statistics Database)


Posted: 20 November 2009
About the Author:

John Gibbons is the Press Secretary for Science at the Smithsonian. He spends much of his time skulking around the collections and research centers sniffing out all the cool science going on at the Institution. In his non-skulking hours, he’s most easily found on a hiking trail looking at anything with feathers.