Human symptoms of Echinostoma infestation include weakness, emaciation, and, in serious cases, hemorrhagic enteritis. Some research suggests, however, that digenetic trematode infection may have other effects in different species. Studies in the 1990s, for instance, indicate that the parasites are likely responsible for some cases of limb abnormalities in amphibian populations. The growth of extra digits or duplicate limbs may be a localized response to the mechanical disruption caused by trematodes encysted in the hindquarters of frogs, salamanders, and other amphibians.