The discovery of the parasite that causes mouse lungworm disease, long associated with Hawaii, at the San Diego Zoo in California has raised concerns that the debilitating disease may become more common.
Hawaii is a hotspot for rat lungworm in the United States, with more than 80 laboratory-confirmed cases of rat lungworm from 2016 to 2026. Despite this, it is still considered a severely underdiagnosed disease. The greatest number of rat lungworm cases occur on the island of Hawaii.
People can contract the disease after finding slugs in washed salads, eating unwashed fruit or vegetables, or even risking eating slugs. Awareness of the disease has changed the way some Hawaii residents shop for produce, where they choose to buy salads or smoothies from and how they prepare fruits and vegetables at home before eating them.
While there have been no human cases in California so far, Hawaii’s experience with the disease is a sign of what California residents and doctors should know about the disease and how to avoid it.
“Probably everywhere”
Susan Jarvi, a Hawaii researcher who studied rat lungworm in the Aloha State for more than a decade and retired last year, told SFGATE she was not surprised to find the virus in Southern California. She said the parasite may be more widespread than people think because it is not tested regularly.
“It could be more prevalent, it could be across the country, especially in the South. It could be everywhere. We know it’s in Louisiana, Texas, Georgia, Florida, so it could be spreading again,” Jarvey told SFGATE.
In the third stage of its life cycle, parasitic Angiostrongylus cantonensis larvae can infect humans. (Kay Howe)
The disease is caused by the parasite Angiostrongylus cantonensis, often called rat lungworm because the parasite’s life begins in mice. The larvae are then passed on to snails and slugs in the mice’s droppings. Humans can become infected if the tiny larvae are accidentally ingested, most commonly through contaminated produce.
In humans, the disease can be serious. Once inside the body, the roundworm parasite travels from the intestines into the bloodstream and then to its final destination in the brain, where it feeds on spinal fluid until adulthood, when it is about 11 millimeters long.
“They can’t leave the brain, so they keep hanging around in your brain trying to escape, and then they die in your brain,” Dr. Jon Martell, a former Hilo doctor, told SFGATE in a story last year.
Rat lungworm symptoms may begin with cough, nausea, and fever but may progress to severe headache, neuralgia, and neurological complications. Prompt treatment with the antiparasitic drug albendazole can help people recover. In some cases, people improve quickly, while others may experience severe, life-changing illness or death.
The introduction of the invasive half-slug in Hawaii in the 1990s made symptoms even more severe, Martell said, because half-slugs can carry 10,000 to 15,000 parasites, while other slugs carry hundreds.
There are currently no half-slug populations in California, but if there were, the pest would likely spread, according to the California Department of Food and Agriculture’s ratings. It’s unclear how California’s slugs interact with the parasite and how many larvae they might carry.
Cleaning alone does not eliminate risk
Since parasites are often transmitted to humans through contaminated produce, cleaning is helpful but does not completely eliminate the risk, Jarvi said.
“You can’t wash that slime off, and you know, slug and snail slime is very, very thick and you can’t really wash it off and there are live parasites in there that can be contagious,” she said.
Invasive semislugs carry extremely high numbers of parasites compared to other hosts. (Kay Howe)
Her first tip is to inspect the product and look for anything unusual. “Sometimes, you can tell if something’s chewing the lettuce or the tomatoes or whatever. I recommend you don’t even handle it. Throw it away. Don’t eat it, you know, because you don’t know what’s chewing it,” she said.
Products should be washed under running water, not soaked, and then dried completely. Javi said she would put the tomatoes on the windowsill, let the sun shine on them, and dry them thoroughly before eating them. The same goes for lettuce, washing it piece by piece. Javi said she even rewashes pre-washed lettuce.
Cooking and freezing are the best ways to kill parasites. “I cook as much as I can,” Jarvi said, adding that even hydroponic lettuce is at risk of contamination from slugs and snails. “I should say, it’s less common than the ones that grow in the ground…but they do crawl.”
defend yourself
In Hawaii, the disease also exposed gaps in awareness among clinicians unfamiliar with the infection. When the parasite reaches the brain and the disease becomes more severe, this can delay diagnosis and treatment.
In the past, residents had to convince doctors to perform the spinal tap needed to diagnose the infection. In at least one case, a slug was brought to Jarvi, who confirmed the infection, and Jarvi sent those results to the emergency room to convince doctors to provide albendazole. Things are improving, but much still depends on a doctor’s familiarity with the disease.
“Education is key. You know, education of the public and education of clinicians is key. If you don’t know anything about it, you don’t even know if you’re looking at it,” she said. “So in my mind, education came first, and it still does.”
SFGATE reached out to the California Department of Public Health for comment but had not received a response prior to publication of this article.
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This article was originally published on Hawaii’s battle against brain-invading parasite shows California what’s possible.
