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Swimmer's itch is a temporary, itchy rash caused by small worm-like parasites called schistosomes (Shiss-toe-soams). These little worms are found in many lakes and ponds in British Columbia, usually in the warm summer months when beaches are busy.
Schistosomes spend their life cycle as parasites in the bodies of water snails and in the blood stream of aquatic mammals, ducks or other waterfowl. Schistosome larvae (lar-vie) leave their snail host and swim around near the surface of the water, intending to come into contact with birds and certain mammal hosts. Larvae sometimes mistakenly get on to the skin of people swimming or wading when they are looking for aquatic mammals or waterfowl.
After a person leaves the water, these microscopic larvae start to burrow under their skin. However, these larvae can not survive in humans and die almost immediately after they burrow into the skin. It is the allergic reaction to these tiny larvae under the skin that causes the itchy rash.
On-shore winds tend to push these tiny larvae to the edges of lakes where the larvae float near the surface. Although less common, cases of swimmer's itch have also been reported at certain coastal beaches in British Columbia - a result of a species of snail from the Atlantic coast.
Young children who wade and splash in shallow areas of lakes and ponds may be at higher risk due to the following factors:
The degree of symptoms will depend on how many of the larvae get onto your skin, and how sensitive you are to them. Symptoms also tend to get worse with repeated exposures.
Swimmer's itch ranges from just a mild irritation to a very severe, itchy red rash. This may become badly infected from too much scratching.
When a person starts to dry off, and the larvae start to burrow into the skin, a tingling feeling may begin almost right away. Small, pin-point sized red spots will soon appear, which grow into larger red rashes within several hours. As these red spots grow, the tingling feeling will be replaced by a strong itch, which feels like a nettles sting or an insect bite.
The itching feeling gradually gets worse, and may last two to five days, or as long as two weeks, before fading away slowly.
Too much scratching can cause severe pain with swelling or other skin infections.
The rash cannot be spread from person to person.
Repeat infections are usually worse because people become more sensitive to the larvae and develop stronger allergic responses each time they are exposed.
The rash and itch can be very irritating, especially for young children, but there should not be any serious danger. However, if a skin infection occurs from too much scratching, you should see your doctor.
There is no sure way to avoid swimmer's itch entirely, unless you avoid lakes and ponds. Before going into any lake that you are not familiar with, find information about the lake by speaking with other people at the lake, local health officials or parks representatives. Some lakes may be posted as having a swimmer's itch problem. Check for warning signs at public beaches and areas.
If you are not sure about a lake, avoid areas with lots of weed growth. There may be more snails around plants, and there may also be more larvae.
There tend to be more larvae near the shore. If there is a pier or wharf to enter the water from, it may reduce your risk of exposure. However, make sure the pier has been approved for swimming. Do not dive into unknown waters! Applying waterproof sunscreen before bathing may help reduce the number of larvae from penetrating the skin.
Most importantly, dry yourself off briskly with a dry towel as soon as you come out of the water. Ideally, you should have a shower and then dry yourself off briskly right away. However, taking a shower will not remove any larvae already penetrated into the skin.
There are a number of steps you can take which may reduce some of the itchiness. Check with your doctor or pharmacist about treatment. Commonly recommended treatments include:
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