Swimmer's itch

What is Swimmer's Itch?

Swimmer's itch is a temporary skin rash that is caused by an allergic reaction to microscopic parasites that are carried by waterfowl, semi-aquatic mammals, and snails. As a part of their life cycle, these parasites are released by infected snails into the water, where they may come in contact with people and burrow into their skin.

The good news is the organism that causes swimmer's itch cannot complete its life history in the human body. Your body's immune system detects it as a foreign protein, then attacks and kills it shortly after it penetrates your skin. The itching and welts are not caused by the organism living under your skin, but by an allergic reaction.

Not everyone is sensitive to swimmer's itch. Some people show no symptoms of swimmer's itch even though others swimming at the same time and place break out severely. Much like poison ivy, however, your sensitivity to swimmer's itch will increase with each exposure. There are several over the counter remedies your pharmacist can recommend to help relieve the discomfort, but see your physician for a definitive diagnosis.

Where does it come from?

The organism that causes swimmer's itch has a complicated life history.

  1. It starts out as a worm (parasite) in the intestinal lining of aquatic birds and mammals (host).
  2. The worms lay eggs inside the the host animal.
  3. The eggs are eliminated by the host and drop to the bottom of the lake.
  4. Then the eggs hatch into miracidia that swim around in the water until they find a snail.
  5. Once they find a snail, they live inside them and develop into cercariae.
  6. The snails then release the cercariae back into the water where they look for another host - aquatic birds, mammals or humans.
  7. When the cercariae find a potential host, they burrow into the host's skin.
  8. If the host is suitable, the life cycle starts all over again.
  9. Humans are not a suitable host and the cercariae die after penetrating the skin.

Swimmer’s itch is not spread from person to person.

Reducing the odds of getting swimmer's itch

The cercariae only live for a day or so and typically swim around in the upper few inches of lake water. This increases their chances of coming into contact with a duck. Once the cercariae is in the duck, it easily moves around the lake as a parasite, and ultimately along the shoreline.

There are actions you can take to help reduce your odds of getting swimmer's itch.

If all else fails...

Copper sulfate may be used to kill the snails which are an intermediate host of the parasite.

For questions on identifying and managing aquatic plants, or swimmer's itch contact the regional DNR headquarters nearest you.