Swimmer’s Itch is an itching rash that occurs in bathers who have been exposed to the larval form of a flatworm that normally infects waterfowl (ducks, geese). Although the larva does not cause any serious illness (it dies quickly in human skin), it can trigger an allergic reaction in those that are senstized.
Swimmer’s itch can occur anywhere that infected snails and birds meet in water, fresh or saltwater. Although reported more commonly on the Atlantic coast, swimmer’s itch appears in the Midwest and now on the Pacific Coast.
A September 27th story in the Oakland Tribune, “Rash on Alameda Beachgoers Blamed on Invading Snail“, reports of increasing incidents of swimmer’s itch occurring in the SF Bay Area where an invasive snail has taken hold in the waterways.
The culprit is a previously unknown parasite carried by the Japanese bubble snail, a ¾-inch snail first discovered in the Bay in 1999 and in Alameda by 2003, that is now abundant on Alameda’s beach. In 2005, about 90 children, many of whom were celebrating the end of the school year, were infected at the beach.
Most reports of swimmer’s itch occur between May to September. This is due to the combination of 1) warming waters leading to snail population growth 2) migrating birds resting in bodies of water, and 3) humans attempting to cool off by unwittingly taking a dip in infested waters.