Rat Lungworm 101: What You Need to Know About This Potentially Deadly Parasite

Did you know rat lungworm has been found on five of the six largest Hawaiian Islands?
Rat lungworm disease cycle
illustration: erica kunihisa


Washing your veggies is common practice. But, until recently, most of us thought we were removing dirt and pesticides—not tiny slugs that carry a parasitic worm that invades our brains.


A recent Hawai‘i outbreak of rat lungworm disease, or angiostrongyliasis, included a San Francisco couple who contracted it on a recent honeymoon, making national headlines. By the end of May, the total number of local infections rose to 15, according to the state Department of Health.


Most cases result from consuming raw or undercooked snails and slugs—particularly invasive semi-slugs—that are infected with the parasite, often found in poorly washed greens or other raw produce.


Rat lungworm is a rare illness, with one to nine cases reported every year and two deaths since 2007. Symptoms can range from very mild—headaches, stiffness of the neck, nausea—to severe, even resulting in temporary paralysis or comas.


Susan Jarvi, a professor of pharmaceutical sciences at UH Hilo, says she’s been researching this disease for more than five years, talking with farmers and residents on the Big Island about what it is and how to prevent it. “On the Big Island, practically everybody knows somebody with rat lungworm disease,” she says. “It’s been going on so long … It’s a fairly preventable disease, if you know about it.”


Many people think that rat lungworm is a problem only on the Big Island and Maui, but the parasite has also been found on O‘ahu, Kaua‘i and Moloka‘i.


In 2013, UH student Jaynee Kim conducted a statewide study for a master’s thesis and found instances of rat lungworm across Hawai‘i: “Numerous gastropod species (16 of 37 screened) tested positive for A. cantonensis, with a large range of parasite load among and within species. The parasite occurs on five of the six largest islands (not Lāna‘i),” Kim wrote.


Fortunately preventing rat lungworm is simple: Wash all veggies and fruits, even ones with skins you’ll peel off. Leafy greens should be carefully washed, front and back, in water (no need for salt, bleach, vinegar or other cleaners). Mikala Minn of Mahele Farm, a 10-acre community farm in Hāna, says you have to wash fruits and vegetables under running water, not soak them in a bowl of water. He recommends peeling bananas from the closed end and not eating any part of the fruit that was exposed. “Slugs are all over bananas,” he says.


You can also cook your produce—heating it to at least 165 degrees—or freezing it for more than 48 hours. Extreme heat and cold will kill most bacteria and parasites, including rat lungworm.


(One additional bit of advice: Never drink straight from your garden hose; slugs or snails could be lurking within.)