Swimmer's Itch

Swimmer's Itch

 Key Points
Condition, sometimes called cercarial dermatitis, is a skin rash caused by infestation by the larvae of a flatworm that typically affects snails and waterfowl.
These cercaria penetrate the human host through exposed skin or the mouth instead of the intended waterfowl or aquatic mammal.
Symptoms begin as red marks from larvae penetration and itching, which becomes more intense a few hours later, occasionally developing into papules, hives, or blisters.
People who have been previously exposed to swimmer's Itch are more susceptible.

Swimmer's Itch, sometimes referred to as cercarial dermatitis, is a skin rash caused by an allergic reaction to infestations of certain parasites of birds and mammals. Immature larva, called cercariae, of parasitic flatworms, called schistosomes, are released from infected snails into fresh and/or salt water. Swimmer's Itch develops on exposed areas of skin after contact with these larva when they penetrate the person's skin. Swimmer's Itch occurs when a film of cercariae-infested water dries on exposed skin.

Cercariae penetrate the skin of a bird or mammal, migrate through the various organs, and reside in the blood vessels, usually those surrounding the intestine. There, the parasites develop to adulthood, when female worms lay eggs that end up in the host's intestines. When the host defecates into the water, the eggs hatch, which is called miracidium. These miracidium swim through the water seeking a specific species of aquatic snail, Lynmnaeidae or Physidae. Once the miracidium find the right snail, they infest them through skin or the mouth. Within the snail, the miracidium form the sporocyst. In about a month, the sporocysts develop into cercaria. These cercaria burrow out of the snail, seeking a bird host to repeat the cycle. Again, this is through either skin penetration or ingestion.

If someone is unfortunate enough to be in the wrong place at the wrong time, the cercariae can penetrate the outer layer of human skin. After the parasite enters the skin, it dies and may cause Dermatitis in individuals who have been previously infected. Larvae are generally infective for 24 hours only, once they are released from the snail. However, an infected snail will continue to produce cercariae for it's entire life, which can be up to two months. Waterfowl are the usual hosts of these flatworms, with humans only infected accidentally. Certain aquatic mammals such as muskrats and beavers can also be a host.

Several combining factors may lead to infection. In summer, the water temperature reaches the appropriate level for snails to reproduce and grow rapidly, migrating aquatic birds infected with the trematode parasite return from their winter habitats or domesticated aquatic birds return to full activity, and people go out swimming.

A swimmer’s first exposure to infested water may not result in any reaction. However, after repeated exposure, sensitivity may develop. Symptoms include an initial itchy or tingling sensation that usually settles quickly, leaving the infected person with tiny red spots at the sites of penetration of the larvae. After a few hours, intense itching may develop and the red spots enlarge to form pimple-like bumps (papules) and occasionally, Hives. Blisters may develop over the next 24 to 48 hours. Untreated, the rash usually settles within several weeks. The rash is usually limited to areas of the body that get exposed directly to water, so skin under swimwear is often protected. People who have suffered swimmer’s Itch before may be more severely affected on repeated exposures.

Differential Diagnosis (Other conditions with similar appearance)
Amebiasis
Hepatitis A, B, C, D, E or Viral
Inflammatory Bowel Disease
Leishmaniasis
Pancreatitis, Acute
Pancreatitis, Chronic
Splenomegaly
Tuberculosis
Typhoid Fever,
Urinary Tract Infection, Male or Female

Diagnosis
Key Points
There are no skin biopsies or blood tests that indicate cercaria infection.

Treatment
Key Points
Toweling off can prevent some cercariae from penetrating the skin.
*Once the rash has developed, there are various lotions and creams that can be used to alleviate and treat itching including calamine lotion and mild corticosteroid creams.

For some species of schistosomes that cause swimmer’s Itch, toweling off may help; with other species, it will not do any good because the cercariae have already penetrated the skin while the person was in the water. Treatment may not be necessary when there are only a few itching spots. Once the reaction has occurred, the skin should be lightly rinsed with isopropyl (rubbing) alcohol and then coated with calamine lotion. An antihistaminic or mild corticosteroid cream (1% hydrocortisone) can be beneficial. If the initial itching is severe, then scratching can cause abrasions and skin infections may develop. Antibiotics may be used to treat secondary infections. If the reaction is severe, oral steroids (Prednisone) may be appropriate. Other treatments that have been recommended include cool compresses, bath with baking soda, baking soda paste to the rash, and colloidal oatmeal baths. Infection can be prevented by avoiding the shallow, warm water areas where snails are prevalent.