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I read in the paper that frogs and toads are becoming scarce and that many of them have extra legs and other deformities. Is this a sign of disease that is causing them to die?

Declines in several amphibian species have been studied for over 20 years. More recent concern about deformed frogs arose with the discovery of large numbers of deformed leopard frogs in Minnesota in 1995, however, scientists agree that deformities are unlikely to have caused the extensive, well-documented declines of many amphibian species worldwide. USGS scientists have described severe declines of several amphibian species in Colorado and California. Although they have observed that many species are absent from historically documented localities, often in national parks and wilderness areas, they have rarely observed deformities. For example, USGS scientist Dr. Gary Fellers has studied declining amphibian populations in California for 9 years. He and his field crews have visited over 4,500 sites and examined over 8,000 frogs and toads. Fewer than 10 of these individuals had any type of deformity. 

Research on deformities provides additional evidence that deformed frogs may occur naturally as a result of parasite infections but does not prove that all deformities are caused by parasites nor that global species declines are associated with deformities. It is probable that deformities in different localities have different causes. In the Upper Midwest, deformities similar to those in wild frogs have been produced in laboratory-reared frogs exposed to water and soil extracts from sites where deformed frogs have been studied. Extracts did not contain the parasite (metacercariae) but did contain chemicals present when samples were taken. Thus, chemical causes of deformities should continue to be explored.

Learn more: USGS National Wildlife Health Center: Amphibian Malformations and Declines

Tags: Fish, Amphibians, Endangered Species, Disease, Health, Frogs