Cercarial dermatitis (swimmer’s itch) is caused by the penetration of human skin by cercariae (larva) of schistosome parasites that develop in and are released from snail hosts.

In 2004, cases of swimmer’s itch among beach visitors at Robert Crown Memorial Beach in Alameda were subsequently found to be caused by an invasive, previously un-described marine parasite. From 2005 to 2008, our District collaborated with the University of New Mexico in identifying the new parasite. The swimmer’s itch was caused by a previously unknown microscopic parasite that was shed by a newly invasive snail-the Japanese bubble snail. This snail was first reported in San Francisco Bay in 1999. This collaborative effort resulted in a publication that summarized the current biology and classification of this parasite.

Presently, there is a “Beach Water/Swimmer’s Itch Hotline” (510.567.6706) to enable the public to report swimmer’s itch cases. Once a case is reported and verified, warning posters are posted at the site to inform swimmers and beach comers of the potential risk and precautions they should take.

Emerging Infectious Diseases: “Cercarial Dermatitis Transmitted by Exotic Marine Snail” Brant et al., 2010