"But we need to remind people that there are serious health impacts of not dealing with invasions.Swimmer’s itch, also known as lake itch, duck itch, cercarial dermatitis, and Schistosome cercarial dermatitis, is a short-term, immune reaction occurring in the skin of humans that have been infected by water-borne schistosomatidae. "People think of invasive species as an environmental problem," Cohen said. Tests in Mobile Bay, Ala., during that period showed the same strain of cholera bacteria in the ballast water of 18 ships that had traveled from South America, Cohen said. In the early 1990s, a cholera epidemic swept Peru, killing upward of 10,000 people. What worries Gaither and Cohen most, though, are incidents like those at Crown Beach, in which invasive organisms have a direct impact on human health. "It impacts ranching, agriculture, management of water resources, natural areas and fisheries." Human health impact "It's hard to estimate the economic damage caused by invasive species," said Jim Gaither, an ecologist with the Nature Conservancy in Sacramento. The freshwater bivalve originated in Russia but has overrun ecosystems around the planet, devouring plankton, clogging water pipelines and choking beaches with their characteristic striped shells. Of all invasive species, the zebra mussel is probably the best known. The exponential growth of global commerce is blamed for spreading a host of nonindigenous plants, microbes and animals around the world.
"I've been swimming here for years," said the Oakland resident. This week, Judith Mader splashed in the water with her two curly-haired granddaughters, Piza, 2, and Maxine, 7 months. Warning signs about swimmer's itch posted at Crown Beach have done little to deter fans of the picturesque spot, however. The San Francisco Bay-Delta, the largest and most important estuary on the West Coast, has at least 234 invasive species of plants and animals and more are being discovered each year. But they may have hitchhiked in shipments of oysters for farming or in the ballast tanks of cargo ships, which are filled with or emptied of water to stabilize the vessels depending on the size of their cargo loads. Researchers can't pinpoint exactly how the Asian snails made their way to Northern California. Over the past five years, researchers say the worm has wriggled into Bay Area beachgoers' bathing suits from the Japanese bubble snail, a three-quarter-inch-long gastropod first identified in San Francisco Bay 10 years ago and in Alameda in 2003. In people, the worms are rejected and the rash subsides in a couple of days, or, at most, in a couple of weeks. Usually, the parasite - a microscopic flatworm with a forked tail - bores into the legs and feet of birds, hitches a ride in the bloodstream and settles in the intestines to breed. It is an immune system reaction caused when a certain type of parasite emerges from snail shells and attempts to burrow into a host's skin. Swimmer's itch, or cercarial dermatitis, normally crops up in freshwater. However, Cohen said the real number might be far higher, since many cases are incorrectly linked to other conditions or go unreported. Seventy-one additional cases have been reported to Alameda County public health authorities since then. In it, researchers detailed the most recent onset when 90 elementary schoolchildren contracted swimmer's itch in 2005 after a visit to Crown Beach for an end-of-the-year picnic.
This month, Cohen co-authored an article on the outbreaks for the journal Emerging Infectious Diseases.
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