One patient treated for rat lungworm disease insists that he got the illness by eating raw 'opihi in Hawai'i, but doctors say that's highly unlikely.

'Opihi is the Hawaiian name for several species of limpet that grow on rocks at the ocean's edge. They are prized in Hawai'i as a traditional food that's often eaten raw at lu'au and other celebrations.

But two University of Hawai'i mollusk specialists say because of the life cycle of the parasite that causes the disease, getting it from eating 'opihi would be a long shot.

"That would be a real surprise," said Michael Hadfield, a zoologist who specializes in marine and land mollusks. "I can't imagine how 'opihi, which live on really wave-pounded, basaltic shores," would get a chance to eat rat dung, he said.

Even if a rat ventured into a tidal area at low tide, the next tide would dilute any droppings, Hadfield said.

"The snails (that are a known carrier of the disease) have to eat rat poop somewhere along the line" to pass on the parasite, Hadfield said.

Angiostrongyliasis cantonensis (rat lungworms) live in the lungs of rats. Worm larvae in rat feces can be transmitted to slugs and snails, freshwater crabs or shrimp, and even lizards, according to medical literature on the disease.

Infected slugs and snails can contaminate raw vegetables. Once inside a person, the parasites can cause a rare form of meningitis, an infection of the spinal fluid.

That's what has happened to at least 33 people in the Islands since 2001, according to state Department of Health statistics.

Two recent Big Island victims are in comas caused by the disease. It's believed they ate raw vegetables contaminated by infected slugs.

Robert Cowie, of UH's Pacific Biosciences Research Center, agreed that an 'opihi contaminated with rat lungworms would be "extraordinarily unusual."

Dr. Francis Pien, an infectious disease specialist, told The Advertiser that one patient he treated for rat lungworm disease a couple of years ago believes he got it by eating raw 'opihi in Hawai'i.

"He will swear to you that's how he got it," Pien said, calling the patient "a very reliable person." The man has since recovered fully and lives on the Mainland.

The patient also could have gotten the parasite via vegetables, Pien said.

Pien said he has treated "at least 20 cases" of rat lungworm disease in 35 years of practice. None of the victims in the past went into comas or died. "Everybody else got well," he said.

Pien maintains that it's possible his 'opihi-eating patient got sick from another food contaminated by the rat lungworm parasite, or that the 'opihi were somehow contaminated after harvest.

"I don't like raw anything myself," Pien said. "Any raw thing, you're taking risk."

Oysters, he said, can be carriers of a potentially harmful Vibrio bacteria that makes people sick. Raw fish, such as sushi, has been the source of infection by the Anisakasis worm, which requires surgical removal of the parasite from the victim's stomach.

While Hadfield isn't worried about rat lungworm in seafood, he warns that any snail or slug in Hawai'i could potentially carry disease and recommends thorough hand-washing after handling snails or slugs.