How to not get a horrible brain parasite on your trip to Hawaii

By Rachel Feltman - March 20, 2019

Angiostrongylus cantonensis larva


You may have read a thing or two lately about the oh-so-grossly-named rat lungworm. This brain parasite isn’t new, but only became routine in the United States in recent years.

Angiostrongylus cantonensis favors tropical climes, and used to crop up only in Asia and some parts of the Caribbean. But after seeing just a pair of cases in the past decade, Hawaii has now had nine reports in three months—six on Maui and three on the Big Island. Patients have included vacationers, so travelers might have cause for concern. And The Atlantic reports that the continental U.S. should not be complacent: the infection now shows up with some regularity in California and along the Gulf Coast, and has even been spotted in Oklahoma.

So whether you’re headed off to a dream vacation in Hawaii or nervously eyeing the news from your couch in Alabama, here’s everything you need to know about these gnarly brain worms.

Angiostrongylus cantonensis, known as the rat lungworm, is spread primarily by rats. The adult form of the parasite—a roundworm that can grow to around 2 cm long—only takes up permanent residence inside rodent pulmonary arteries.

But it can still infect humans—and it goes for the brain. Here’s how: snails and slugs are intermediary hosts of the parasite, infected by its tiny larvae. The parasites don’t fully mature into adults until they end up inside a snail-guzzling rat, but these teenage worms can unwittingly find human hosts instead.

Once larvae enter the human bloodstream, they head to the central nervous system.

According to the Centers for Disease Control and Prevention, infection with rat lungworm is usually not something that requires treatment. The parasites will die off on their own within a year or so, because humans are a dead-end host—we can’t support their development to sexual maturity, and we can’t pass them along to another animals. The question is how your immune system will react to that process.

In some cases, the parasite’s presence around the brain can cause eosinophilic meningitis. Basically, an uptick in the number of a certain kind of white blood cell—your body’s totally understandable reaction to a freakin’ worm rummaging around in your skull—causes severe inflammation of the membrane that covers the brain and spinal cord. The symptoms include headache, stiff neck, tingling or painful feelings in the skin, low-grade fever, nausea, and vomiting, and these are signs to seek medical treatment. There’s no cure for the parasite, but doctors can manage your symptoms until your body’s gotten rid of the bugs for good. But this waiting period can be unpleasant for some.

“If you could imagine, it’s like having a slow-moving bullet go through your brain and there’s no rhyme or reason why it’s going to hang out in this part of the brain or that part of the brain,” Hawaii’s state epidemiologist Dr. Sarah Park told the Associated Press. Descriptions of symptoms from patients with the worst of it are, to put it simply, terrifying. And while most people who get eosinophilic meningitis will be fine, severe meningitis can be fatal or cause permanent damage.

In other words, infection with rat lungworm is generally not a big deal, but it can be pretty nasty if you get unlucky.

Good news: no matter where you live, you’re not going to pick up Angiostrongylus cantonensis by walking around barefoot or smooching someone who’s riddled with brain worms. It’s easy to get infected accidentally, but only if you don’t take some very simple precautions.

Humans get infected by swallowing bits of animals that carry the parasite larvae—just like rats do! So don’t eat undercooked, or raw snails or slugs. In fact, crazy idea here, maybe skip the escargot entirely if you’re in an area with recently reported infections. And keep an eye on any babies or toddlers you’ve got running around—apparently kids like to eat slugs sometimes.

Of course, not everyone who’s gotten sick has wittingly swallowed a snail. Even a teeny tiny bit of slug stuck to raw produce can actually make you sick, so washing fresh food properly is crucial. In fact, the CDC recommends avoiding raw produce entirely if you can help it. But, like, it’s Hawaii? You want to eat that sweet, sweet produce. Just make sure to wash each leaf of leafy veggies individually, and take care even with produce that might seem safe, like pineapple; you could definitely pick up a bit of slug from the outside in the process of cutting up the sweet berry flesh inside, so rinse before you cut. You should even wash bananas before you peel them. Really!

And this should go without saying, but wash your hands, too—after spending time outside, and before cooking. You don’t want to accidentally ingest tiny snail bits because you didn’t clean up after a hike.

There’s also evidence that animals such as freshwater shrimp, crabs, and frogs can be infected with larval parasites too, so you might want to avoid any creepy crawlers that haven’t been thoroughly cooked. Fish do not carry the parasite, according to the CDC, so your bowl of poke is safe. Unless it has unwashed produce or snails in it.