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Joseph Kiesecker Background: For the past ten years, biologists have been puzzled by the apparent epidemic of frog limb deformities seen in Canada and the United States especially in the West, Midwest, and Northeast. Researchers are unsure whether the dramatic increase relates to increased awareness or environmental changes, but a variety of studies have sought to link the deformities and the dwindling number of frogs to ultraviolet radiation exposure, chemical pollution, predation, parasites, or disease outbreaks. Earlier reports by Kiesecker have suggested that extremely dry climatic conditions cause increased exposure to ultraviolet radiation which in turn causes immune dysfunction leading to decreases in population density resulting from increased susceptibility to diseases and parasite infestation. Advance: In the current study, Kiesecker reports field and laboratory studies that conclusively demonstrate that trematode infection was required for the development of limb deformities in wood frogs. Deformities were more common at sites adjacent to agricultural runoff. The laboratory studies corroborate the association between pesticide exposure and increased infection with pesticide-mediated immunocompetency as the apparent mechanism. Implication: The immune effects in the laboratory studies were seen at pesticide levels within the current EPA drinking water standards. Similar adverse effects are seen in other amphibians in other regions and may be explained by the widespread use of pesticides. Whether similar adverse effects are seen in other animal species remains to be determined, but the fact that these effects are seen at relatively low pesticide concentrations, suggests major public health implications and the possibility of the need for more stringent pesticide regulation. Citation: Kiesecker JM. Synergism between trematode infection and pesticide exposure: A link to amphibian limb deformities in nature? PNAS, July 23, 2002, v. 99:15, 9900-9904. |
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