The life cycle of swimmer’s itch.
What is Swimmer’s Itch?
Cercarial dermatitis, also known as “swimmer’s itch,” is an uncomfortable rash caused by microscopic parasites found in freshwater lakes. These tiny parasites naturally cycle between birds, snails, and mammals in the lakes. When the parasite larvae enter human skin, they cannot survive and soon die. This contact is what causes an itchy allergic reaction. Symptoms such as burning, itchy red pimples or small blisters typically appear within 12 hours and may last over a week. Not everyone reacts to swimmer’s itch, but like poison ivy, sensitivity can increase with repeated exposure.
Swimmer’s itch relies on a diverse list of hosts to complete its life cycle, and it maintains a natural ebb and flow in cases from year to year due to changes in its host animal populations.
This year, the GLA has received reports of increased cases of swimmer’s itch.
The Swimmer’s Itch Cycle is Complex in Glen Lake
Swimmer’s itch has a remarkably complex life cycle in Glen Lake. Multiple species of waterfowl including mallards, mergansers, and Canada geese serve as hosts for several species of parasitic flatworms. Those parasites, in turn, rely on multiple species of aquatic snails as intermediate hosts. Many birds can carry multiple parasite species, and many snails can host more than one parasite, creating an intricate web of interactions. Because there are so many host and parasite combinations, eliminating any single bird or snail species would not break the cycle. This complexity is why management efforts focus on reducing swimmer’s itch risk through science-based monitoring and targeted interventions, rather than attempting to eliminate the parasite entirely.