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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

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A: Skin of a patient showing the inflammatory response to cercariae in the skin.