Avoid rat lungworm disease by washing all local produce

Kokua Line has received several questions about rat lungworm disease in recent days, thanks to an uptick in cases that has readers asking how to wash local produce and whether it’s safe to walk barefoot in the yard, and about the snails and slugs that transmit parasitic worms to humans.

We’ll address them with the help of Robert H. Cowie, a research professor at the University of Hawaii-­Manoa’s Pacific Biosciences Research Center. Cowie, a mollusk expert, guest-edited a June 2013 supplement to the Hawai‘i Journal of Medicine & Public Health that focused on rat lungworm disease, which was first reported in Hawaii in 1961. You can read the 88-page journal at 808ne.ws/hjmphrat.

First, a recap: Rats carry a parasitic nematode (roundworm), which they shed in their feces. Snails and slugs eat rat feces and become carriers. Humans can become infected when they ingest raw or undercooked snails or slugs; sometimes tiny ones clinging to fresh, raw produce are ingested accidentally. The parasitic worms travel to the afflicted person’s brain and can cause severe symptoms, including a type of meningitis.

Question: Regarding the story about rat lungworm disease in Monday’s Honolulu Star-Advertiser (808ne.ws/april9sty), is this rat lungworm in all of our locally grown produce or does it like certain vegetables? We wash our lettuce, leaf by leaf, but should we also rinse it in salt water before eating? Can you provide us with more information?

Answer: Snails and slugs that transmit the worm are widespread in Hawaii and could presumably be on any type of local, raw produce. But they are easier to see on, and therefore rinse off from, smooth-skinned produce like tomatoes or cucumbers. Tiny snails and slugs are harder to detect on leafy greens such as lettuce. Cowie’s practice is to carefully wash each leaf, front and back, with plain cold tap water. There’s no need to add salt, he says. Controlled experiments showed that plain water removed snails just as well as solutions containing bleach, vinegar and salt water or commercial produce-washing agents, he said. (See page 83 of the journal.) “The best advice is to wash all your produce, no matter where it’s from. There are other things to worry about besides rat lungworm, like bacteria, pesticides, etc. So, rule No. 1, wash your produce,” Cowie said. Cooking kills the snails and worms, so cooked vegetables such as steamed spinach and kale are unaffected.

Q: Why are they only talking about Hawaii produce?

A: Because rat lungworm disease has not been reported in U.S. locations other than Hawaii and a few places in the Southeast where the weather also is warm and humid. It is present elsewhere in the world. In southern China, for example, an invasive apple snail that is eaten raw as a delicacy is “strongly associated with rat lungworm disease. Don’t eat (snails) raw,” Cowie said.

Q: Some people don’t even want to walk around barefoot in the grass, thinking they’re going to step on a snail. Can you really catch it that way?

A: “I’d say that’s highly unlikely,” said Cowie, who knows of no evidence of anyone contracting the disease by stepping on a snail, slug or slime, or of contracting it through an open wound. “Personally, I think it’s fine to walk around barefoot in the grass.”

Q: What about the slime from slugs? I see the trails on my lanai every morning.

A: There are far fewer worms in the slime. Even a quarter-inch snail can carry thousands of worms, while its slime might have one or two, Cowie said. The severity of symptoms in an afflicted person depends in part on the number of worms ingested. To be safe, avoid touching snails, slugs or slime with your bare hands. Wash hands thoroughly if that does occur.

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