Jenifer Dugan, Mark Walter and Carrie Culver of the Marine Science Institute at the University of California at Santa Barbara analyzed tissue samples from more than 800 mitten crabs collected in the bay -- not a single crab was shown to be infected with either Asian or North American lung flukes. The crabs were collected at 15 to 20 sites over a two-year period beginning in 1999.
Dugan said, "We have not found any evidence of lung flukes. There have been a few other parasites found, but only in a couple of specimens. The crabs seem to be healthy and thriving. Nonnative species may flourish in a new habitat because they have escaped many of their native predators and parasites."
Lung flukes are parasites with a complex lifecycle that requires them to infect two intermediate hosts before they mature into adults inside a warm-blooded animal or person. Flukes in their "larval" form infect snails, then crustaceans, such as mitten crabs and crayfish. In mammals, they attack the respiratory system as they breed.
In Asia, where mitten crabs are a delicacy, people regularly suffer lung damage from eating infected seafood. The flukes can also spread to the brain.
State health officials have been concerned that mitten crabs in the San Francisco Bay area might also be carrying lung flukes and putting recreational fishers at a health risk. Although commercial fishing for the crabs is prohibited, sport fishing is allowed, and people do eat the crabs. Live females with eggs can sell for more than $20 per crab in Asian markets, although the sale and transport of live mitten crabs is illegal in California, an effort to curb their spread.