Swimmer’s Itch

An interesting phase of schistosome biology concerns cercarial dermatitis or “swimmer’s itch”. Cercariae of species that normally infect birds (waterfowl and shorebirds) and other vertebrates, especially certain mammals (e.g., muskrats and mink), attempt to penetrate the skin of humans. In doing so, they sensitize the area of attack, resulting in itchy rashes. Because humans are not suitable definitive hosts for these cercariae, the flukes do not enter the bloodstream and mature, but die after penetrating the skin. One of the most common causative agents of marine swimmer’s itch on both the east and west coasts of North America is a blood parasite of seagulls, the larval stage (cercariae) of which develop in a common mudflat snail.