Picture this: you spent the day swimming in one of Michigan’s many lakes. After a while, you notice the formation of red, itchy blisters on your legs. What are these blisters? How did it happen?
The red itchy blisters form a rash called cercarial dermatitis, colloquially known as swimmer’s itch, and is caused by parasitic activity in the water. The cercariae of some species of schistosomes (the larval form of a parasite that requires two hosts to complete its life cycle) penetrate the skin and enter the blood vessels of waterfowl.
Parasite eggs located in waterfowl feces are then released into the water which hatch into miracidia that develop in their intermediate hosts, snails, before producing cercariae that infect the parasite’s second host, waterfowl. Sometimes the parasite may try to enter the blood vessels of a second non-viable host: humans. The parasite burrows into human skin causing the rash, but it cannot survive in humans and move forward in its life cycle.
These parasites “like to move towards the light towards the surface of the water, where ducks and geese would float and swim, and they try to infect a bird,” said Dr. Thomas Raffel, associate professor at the Oakland University. . “They [the parasites] cannot complete their life cycle in a person, but they will still try to penetrate our skin which is the infection mechanism that causes swimmer itch.
The incidence of swimmer’s itch is unpredictable, but there may be factors that increase the likelihood of contracting it. Dr Raffel was part of a research team that studied how windy conditions influenced the incidence of swimmer’s itch on a private beach in Crystal Lake in Northwestern Michigan, Assembly Beach d summer of Congress (CSA).
Over the course of four summers, CSA beach lifeguards recorded various data points, including total number of swimmers and self-reported swimmer itch cases, water temperature, wind speed and wind direction. .
The researchers analyzed this data and found that swimming near CSA Beach in the morning or on days with direct wind from the shore perpendicular to the shore indicated the greatest risk of contracting swimmer’s itch. The light produced at sunrise can lead to an increased presence of avian schistosome cercariae in the morning, and the wind can move these cercariae to swimming areas near the beach. It’s important to stress that it is not the wind that directly increases the risk of contracting swimmer itch, but rather the way the wind moves water carrying the avian schistosome cercariae that humans might be exposed to.
While these results may not apply to other lakes or locations in Crystal Lake due to their unique biological nature, it is important that the data collected at the ASC be consistent over a long period of time. Further research on the subject is needed.
To reduce the risk of getting swimmer’s itch, the Mayo Clinic recommends avoiding swampy swimming spots or where swimmer’s itch is common, not feeding ducks near swimming spots, and rinsing exposed skin. with clean water after swimming.