12 year old boy with itchy bumps after swimming at lake cabin.
What is your diagnosis?
Swimmer's Itch also known as cercarial dermatitis is a distinctive papular eruption caused by penetration of the skin by the cercariae of nonhuman schistosomes. This cutaneous schistosomiasis is usually limited to the exposed areas of the body. It is commonly associated with fresh water lakes, although a related condition known as "clam digger's itch" has also been reported from the salt water tributaries in the Long Island Sound area of New York. The cercariae responsible infect birds, rodents, or undulates and belong commonly to the species Schistosoma. Cercarial dermatitis is a potential hazard worldwide wherever people share an aquatic environment with vertebrates and mollusks harboring schistosomes. These blood flukes require an intermediate snail host and a definitive vertebrate host to complete their life cycle. Inasmuch as humans are an accidental host, complete development cannot proceed and clinical manifestations of cercarial penetration resolve spontaneously within a week. A prickling sensation lasting minutes to an hour after exposure results from exposure to the schistosome infested waters. Pruritic erythematous macules, papules, and occasionally papulovesicles and wheals can be seen soon thereafter. Repeated exposures can also produce a more severe reaction. Postinflammatory hyperpigmentation is a common sequela. Edema, lymphangitis, and regional adenopathy develop in some individuals, as may eosinophilia and systemic symptoms of generalized urticaria, nausea, and vomiting. Once again, repeated exposures produce more severe insect bite reactions, with perivascular lymphocytes with more severe bite reactions.
Treatment is oriented toward the relief of symptoms. Oral antihistamines, topical steroids, and topical antipruritic agents may be helpful. The rash may be prevented by toweling off vigorously and showering promptly after fresh water bathing.
Charles E. Crutchfield III, MD
References: Pocket Guide to Cutaneous Medicine and Surgery by Dover, Arndt, LeBoit, Robinson, and Winthrob
Clinical Adjunct Associate Professor of Dermatology
University of Minnesota Medical School
Medical Director, Crutchfield Dermatology