"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.

But "what was most intriguing," Johnson said, "was that the locations of hot spots had changed substantially over the last decade."

For instance, ponds where scientists had found few "grotesque" frogs in 1999 now had 30 percent or more frogs with deformed limbs, he said. Likewise, former hot spots now had fewer of the diseased amphibians, according to their results, which are not yet published in a journal.

Because some of the hot spots can house threatened or endangered amphibians, conservationists need to know where the parasite is moving.

Predicting future hot spots by keeping track of environmental factors—for example how land is used—may also help scientists figure out what's happening to amphibian populations.

"These severe malformations—even though it's not in the headline news—these continue to occur in a lot of amphibian populations in the western U.S.," said Johnson, who received funding from the National Geographic Society's Committee for Research and Exploration. (The Society owns National Geographic News.)