Amphibian deformities and Ribeiroia infection: an emerging helminthiasis.

Since their widespread appearance in the mid-1990s, malformed amphibians have evoked fear, as well as fascination within the scientific and public communities. Recent evidence from field and laboratory studies has implicated infection by a digenetic trematode--Ribeiroia ondatrae--as an important cause of such deformities. Ribeiroia spp. have a complex life cycle involving planorbid snails, amphibians and water birds. Under natural conditions, malformations might promote parasite transmission by increasing the susceptibility of infected amphibians to predation by definitive hosts. However, with respect to the recent outbreak of deformities, we suggest that exogenous agents (e.g. pesticides, nutrient run-off, introduced fishes) might be interacting with Ribeiroia, resulting in elevated infection levels, and we highlight the need for studies incorporating multiple stressor dynamics to further explore this problem.