The disease that struck Hawaii this year is spread from rats to particular types of snails and slugs. Here’s how to avoid getting infected.

A holiday in Hawaii conjures up images of beautiful beaches and ocean views — a tropical paradise.

What is less likely to come to mind is a brain-invading parasite known as a rat lungworm.

But that was the reality for newlyweds from California, who contracted the disease while vacationing on Maui.

The couple are two of at least nine reported cases of the disease in Hawaii so far in 2017.

Experts say the rising number of cases is worrying.

“It’s concerning for everyone. People’s health is at risk and produce growers’ livelihood is at risk,” Robert Cowie, PhD, a professor at the Pacific Biosciences Research Center at the University of Hawaii, told Healthline.

Read more: Dengue fever outbreak in Hawaii »

Rat lungworm (Angiostrongylus cantonensis) is a form of parasitic worm.

According to the Centers for Disease Control and Prevention (CDC), the adult parasite is found in rats, which pass the larvae of the parasite in their feces.

Snails and slugs then get infected by ingesting the larvae from the feces.

Humans can become infected with the disease by ingesting raw or undercooked snails or slugs that have been infected by the parasite.

It is also possible to come into contact with the disease by eating raw produce like lettuce that hasn’t been properly washed and may have been contaminated by snails or slugs.

The effects vary and can include cold and flu-like symptoms, paralysis, coma, and in rare cases, death.

James Creecy, PhD, assistant professor at the University of Central Oklahoma’s Forensic Science Institute, has done research into the expansion of rat lungworm in the United States.

He says the disease can in some cases lead to serious complications, like meningitis.

“Eosinophilic meningitis is better described as white blood cells in the cerebrospinal fluid. Other symptoms include cranial nerve abnormalities, ataxia [loss of full control of bodily movements], encephalitis, coma, and rarely death,” he told Healthline.

“While this all seems very bad,” he added, “the disease is rare and there is an effective treatment for human infections. Infected wildlife are not as fortunate.”

The CDC says that common types of treatment are for symptoms of the infection, rather than rat lungworm itself. Even without treatment, they say, the parasite will die over time.

Read more: Once again, Hawaii named the healthiest state »

Robert Hollingsworth, PhD, is an entomologist for the U.S. Pacific Basin Agricultural Research Center, based in Hilo, Hawaii.

He has done research on a species of semi-slug (Parmarion martensi) that has been on the Hawaiian Islands since at least 2004.

“Semi-slugs were new pests on Hawaii Island when I was asked to investigate an outbreak in 2004. The residents reporting the outbreak had all become sick from sharing a salad. That’s why I sent off specimens to the CDC for testing. The specimens were highly infected,” he told Healthline.

Semi-slugs are considered especially dangerous in the spread of rat lungworm disease.

“This species is high risk because it likes to climb, is relatively fast moving, and quickly locates rich food sources, and because specimens are likely to be infected by rat lungworm. More so than many other slug/snail species, they avoid soil and favor plastic and building materials. They have a penchant for getting in harm’s way,” Hollingsworth said.

“I think of them as a ‘trash’ species that does particularly well around residences due to hiding places and the types of materials found around residences. In fact, inside and under trash cans are a favorite hiding place,” he added.

Cowie agrees the latest spate of incidences of the disease is most likely due to this species of semi-slug.

“The current outbreak on Maui seems associated with a particular species of slug [Parmarion martensi] that we know to be a very good carrier of the worms. So if the outbreak is related to this species, why is it only happening now? Maybe because it has become more abundant and widespread,” he said.

Read more: Zika virus probably won’t travel far in the United States »

Kathleen Howe became interested in rat lungworm after her son was infected with the disease.

With Susan Jarvi, of the University of Hawaii, she formed the Hawaii Island Rat Lungworm Working Group.

“My son contracted rat lungworm disease … was in the hospital for four months and in a coma for three months. He suffered a lot of brain and nerve damage and was not expected to recover,” Howe told Healthline.

“I became interested in research and education because there was no apparent research or education happening,” she added.

Jarvi, PhD, a professor of pharmaceutical sciences at the University of Hawaii at Hilo, says it is important people understand the dangers of rat lungworm and take proper precautions against the disease.

“Wash vegetables thoroughly … It’s also important to be educated about it and implement proper vector control,” she told Healthline.

Experts advise people to minimize the areas slugs and snails may like to hide (such as in mulch, under plant pots, and piles of wood) and to use approved baits. It’s also important to get rid of rats.

Jarvi agrees the spread of the disease is most likely due to semi-slugs, but she believes there may also be another factor.

“The lack of action in control by the state also likely contributes,” she said.

The Hawaii Department of Health did not respond to Healthline’s request for comment on this story.