Clinical Features:
Cercarial dermatitis (swimmer's itch) is a cutaneous inflammatory response usually associated with penetration of the skin by cercariae of bird schistosomes.  Symptoms include reddening and itching of exposed skin in the water or immediately after emerging.  This is an indication of initial penetration of the cercariae.  After a period of approximately 12 hours, pruritic papules may become vesicular.  Scratching the affected areas may result in secondary bacterial infections.  An interesting note is that previous contact with cercariae can lead to a more immediate and intense immune response.

Laboratory Diagnosis:
Specific snails that would be suitable hosts for these particular avian schistosomes (such as Nassarius obsoletus, the intermediate host for the duck schistosome Austrobilharzia variglandis) need to be collected from the area where cases of cercarial dermatitis have been reported.  The snails need to be checked to verify if they are shedding cercariae by standard methodology.  Sunlight may be preferred over using artificial light to stimulate shedding.  Another method is to crush the snails and examine the body for parasite sporocysts and/or cercariae.  The cercariae then must be identified as being a type that can cause cercarial dermatitis by using appropriate reference material.

Diagnostic findings

• Microscopy

Treatment:
Most cases do not require medical attention.  Topical use of corticosteroid cream may be used for relief.  In addition, cool compresses, bathing with baking soda, applying baking soda paste to the rash, and anti-itch lotion may also be tried.  Scratching the affected area may cause the rash to become infected.  See recommendations on the Division of Parasitic Diseases (http://www.cdc.gov/ncidod/dpd/) Web site for additional information.

Reference:

CDC. MMWR 1992 April 10;41 (14):225-228.