A flatworm parasite called Ribeiroia ondatrae infects several species of frogs just as they're developing their limbs, causing an assortment of defects such as no legs or even multiple legs that jut out at weird angles from the frogs' bodies scientists say.
The deformed frogs are often unable to move and either die or quickly get eaten by predators.
Scientists already knew that the parasite was the culprit in the frog malformations, but the researchers wanted to find out whether known hot spots of Ribeiroia populations in four western states had changed since they were last surveyed in 1999.
So in 2010 Pieter Johnson, an ecologist at the University of Colorado at Boulder, and colleagues gathered data on frogs and parasites in 48 wetlands in California, Oregon, Washington, and Montana.
The scientists found that the parasite infections were still pervasive in amphibians at the study sites.
"We found that, although the distribution of Ribeiroia across wetlands changed, there was little net effect on overall parasite prevalence, with 31 percent of wetlands gaining the parasite and 27 percent losing the parasite," according to the study.