By Christine Hitt

It starts with a headache. Symptoms sometimes resemble the flu, with nausea, coughing and a fever. But it’s actually extremely small roundworm parasites traveling inside the stomach. By the time doctors diagnose neuroangiostrongyliasis, commonly known as rat lungworm disease, it can be severe to the point where the parasites have already reached the brain.

“Hawaii Island is really the epicenter of the disease for the entire country,” said Kay Howe. In late 2008, her son contracted the disease while living in the Puna District of Hawaii Island at the age of 23. He went into a coma and was in the hospital for months; it changed his life forever. Howe has since become an advocate committed to raising awareness, receiving a master’s in tropical conservation biology and environmental science at the University of Hawaii at Hilo and working in Hilo’s Jarvi Lab, which specializes in rat lungworm.

The life of the parasite begins in a rat, which then passes the parasite’s larvae through feces to snails, slugs or other animals that ingest the parasite. People can accidentally or intentionally (such as through a dare) come in contact with the parasite by eating a slug, snail or other infected carriers. But unless someone is taking a bite into a spring roll and sees a half-eaten slug, most times, people aren’t sure how they get the disease.

“Don’t eat raw food in Hawaii,” said Howe, who is even leery of restaurant safety protocols. “This is a tropical place. There’s a parasite, and we advise to cook everything.” She added that any “headed vegetable,” such as lettuce or cabbage, has to be “taken completely apart” and “washed leaf by leaf” under running, potable water, then dried.

Franny Brewer, the program manager for the Big Island Invasive Species Committee, said that she wouldn’t recommend roadside smoothies with greens. “I know it’s very popular. It’s very healthy. But if you haven’t been able to inspect the kale yourself, I wouldn’t recommend that you include that,” Brewer said. She also said people should ask Airbnb hosts in the area how they are filtering their water, as slugs can get into water catchment tanks if they aren’t properly maintained.

Depending on the practice, clinicians sometimes require a diagnosis to give an antiparasitic medicine, such as Albendazole. But there is no simple test to diagnose rat lungworm disease, as it requires a spinal tap.

Many people are often unaware that they may have the parasite, especially since the symptoms resemble the flu. Generally, locals know about the disease, but there are few, if any, initiatives aimed at educating visitors. There are large, uncontrolled populations of rats and slugs, Brewer said. But above all, getting a diagnosis quickly enough or finding an informed doctor who recognizes it right away are two of the biggest issues for patients.

“We often have to fight a doctor to get them to deliver [the Albendazole],” Howe said. “You know, they’ll be, ‘Oh, wait until symptoms develop.’ And it’s like, you don’t want to wait for symptoms to develop. That’s how bad this is. You know, once it’s in your brain, it’s in your brain.” In her experience talking with people — and in the case of her son — doctors often refuse to test for rat lungworm, not believing it to be the culprit.

“The people who are in the ER with symptoms, they have to somehow convince the doctor to give them a spinal tap,” Howe said, adding that Susan Jarvi, the founder of Jarvi Lab, has had to accompany people to the emergency room and show lab results proving a host such as a slug was infected.

“That is still going on, which has been extremely frustrating because I don’t have the capacity to educate the medical professionals,” Howe added. The Centers for Disease Control and Prevention website is also an issue, she said, and it’s outdated, resulting in misinformation.

The CDC website currently states that some people with rat lungworm will either have no symptoms or mild symptoms that don’t last very long, adding that “there is no specific treatment” and that “most infections resolve on their own.”

After reaching out to the CDC, and the agency responded, “The parasite dies over time, even without treatment. Even people who develop eosinophilic meningitis usually don’t need antiparasitics … Given the limited data available and the lack of randomized, controlled trials for treatment options, some questions remain. CDC supports the conclusion of the Hawaii guidelines — the decision to use anthelminthics [antiparasitic drugs] should be made on a case-by-case basis.”

From 2014 to 2023, there were 80 laboratory-confirmed cases of rat lungworm in Hawaii. Both residents and visitors are affected by the disease. In 2017, two newlyweds from San Francisco who were on a two-week trip to Hana on the island of Maui contracted the disease, leading to several medical operations. So far in 2025, there is one case.

But according to Howe and the Hawaii State Department of Health, rat lungworm is an underdiagnosed disease.

“Not everyone wants to get the spinal tap or is able to get the spinal tap at the time where the diagnosis could be made, so there are certainly misdiagnoses,” said Dr. Sarah Kemble, an epidemiologist at the Hawaii State Department of Health.

“We find that a lot of visitors have never heard of it or might not realize that it’s endemic in our state, and we want people to know what they can do to protect themselves,” she continued. “Don’t eat raw snails, slugs, freshwater shrimp. And visitors should be aware that when they buy locally fresh fruits and vegetables, they should wash them very carefully before consuming them.”

The disease occurs on all of the Islands, but the vast majority of cases happen on Hawaii Island, and the Puna District is ground zero. Outside of Hilo, Puna is known for its rainforests, small farms, off-grid residences and unique Airbnbs. Many people frequent farmers markets, grow food themselves and eat all-natural food. But the environment is also a thriving one for rats, snails and slugs.

Dr. Jon Martell, an internal medicine physician, has seen CAT scans showing the damage done by the worms once they’re ingested. He worked at the Hilo Medical Center on Hawaii Island for nearly 27 years, retiring in 2022, and he was also the chief medical officer from 2015-2020. Martell became known as the “rat lungworm guy” who took care of most of the cases, particularly the severe ones.

“It burrows through the intestines,” Martell said. “In severe cases, people have nausea and stomach pain before the headache comes. Then they burrow through the intestines to the bloodstream. They go up to the brain. They get access to the brain, and that’s when the headache starts.”

The parasites don’t eat the brain, Martell pointed out. They drink the spinal fluid around the brain. When the worms reach adulthood, growing to a size of around 11 to 12 millimeters, they try to leave the brain but can’t.

“They can’t get out of the brain, so they keep wandering around inside your brain trying to get out, and then they die in your brain,” he said. “You can see the actual tracks where the worms have burrowed along trying to get out.”

Patients who survive are often left with disabilities, such as those linked to memory problems, fatigue and nerve pain. “It’s a nasty disease,” Martell said.

Martell, who first encountered rat lungworm in the 1980s, said the cases used to be mild. Pain medicine was the treatment, and patients would get better. But he saw that shift drastically in the early 2000s.

“Right about 2008, everything changed,” Martell said. The cases started trending severe. “We were seeing people coming in with absolutely horrible pain, not just headache, but nerve pain everywhere to the point that they needed to be hospitalized, and in some cases, they either had severe brain damage or death.”

The shift likely coincided with the introduction of an invasive semi-slug that has since spread. While other slugs carry “maybe as much as 100 of those juvenile rat lungworms, the semi-slug would have 10,000 or 15,000,” Martell said. “So what was happening, instead of getting four or five worms and getting a bad headache, you were getting 1,000 worms in your brain and getting severe brain damage.” It all depends on the number of worms swallowed, he added.

Brewer of the Big Island Invasive Species Committee said that it would be impossible to stop the disease in Hawaii because that would mean trying to rid the islands of rats, slugs and snails. When asked if the situation could get worse, she said, “Hawaii Island is the worst-case scenario,” but she added that she has concerns about the disease spreading to other states.

Rat lungworm is already in the southeastern United States, said Jarvi, but she added that the region doesn’t currently have the semi-slug, so there are only a few cases. “That’s how Hawaii was before the semi-slug,” she said. Her lab is working on trying to make blood-based diagnostics a possibility so a spinal tap test won’t be necessary.

Howe, now living in Colorado eight blocks away from her son, said her son is able to live independently but is permanently disabled, with his vision and short-term memory affected.

She published a memoir three years ago to educate the public of the disease and wants people to take it seriously, even though it’s considered rare. “When you have seven serious cases a year or 15 serious cases a year amongst a relatively small population on Hawaii Island, that’s not really rare anymore,” she said.

“The severity of the disease and the fact that you may never, very well ever, recover the quality of life that you had,” she continued. “You shouldn’t be looking at case numbers. You should be looking at severity.”