A few years ago I heard about a weird disease on the Big Island. I live on Maui so I didn’t worry about it.

A few months ago I heard about an alien slug on Maui. I didn’t worry about it.

When two Maui friends got sick from a disease transmitted by slugs, I started to worry. Now I will never see a salad, my garden and my yard the same way again.

A “semi-slug” is seen in East Maui in this photo taken March 22. Courtesy of Maui Invasive Species Committee via Dr. Robert Cowie

A week ago my neighbor four doors down took a picture of a half snail-half slug in his yard and posted it on Facebook. With his permission, I sent the photo to the Hawaii Department of Health. State epidemiologist Sarah Park forwarded it to mollusk expert Robert H. Cowie at the University of Hawaii Manoa.

“Yep, that’s the so-called ‘semi-slug’ generally identified scientifically as Parmarion martensi,” said Cowie, research professor at the Pacific Biosciences Research Center. “It has not been previously reported on Maui in any medium and has only in the last couple of weeks come to my attention as being present on Maui.”

The creature was known to exist on the Big Island and Oahu, but “people are saying it has been around on Maui for at least four years,” Cowie said. “There is concern that its presence is associated with a number of recent rat lungworm disease cases on Maui.”

‘A Particularly Good Carrier’

Now we all should worry about the potentially lethal rat lungworm disease and a near-perfect carrier slug that loves our parks, yards, gardens and veggies as much as we do.

In phone interviews and email exchanges, Cowie said that confirmation of the new mollusk find on Maui “adds to this being a very fluid situation.”

“We need to be concerned about all slugs and snails, but the semi-slug is a particularly good carrier of rat lungworm … 80 out of 100 of these slugs can test positive for the worms.”

According to the Health Department, there have been 58 recorded cases of rat lungworm, most of on Hawaii Island. Cowie notes that “the DOH is conservative in its definitive records.”

“Worms develop in the brain, grow bigger and start moving around in the brain, looking for a way out.” — Robert H. Cowie, University of Hawaii Manoa

The only previously confirmed case of a Maui resident contracting rat lungworm was in 2010. But this March another case was confirmed and Health Department officials are looking into four more possible victims.

These developments will change two daily habits for me – no more going barefoot in the yard, a delight since infancy, and a much more vigilant, vigorous washing of fruits and vegetables, especially Hawaii-sourced leafy greens.

Rats host the lungworm. Slugs and snails eat rat waste and become carriers of parasites that can migrate to human brains in a day, causing eosinophilic meningitis. Other known carriers are freshwater prawns, crabs and frogs. Fish do not spread the parasite.

This photo of a semi-slug was taken March 28 in the Hana area. Courtesy of Kawika Kaina

Dr. Lorrin Pang, Maui’s district health officer, has been searching for the semi-slug for four years, first on Hawaii Island. On his second trip to the Puna district in early March, “I turned over my first rock and found five of them.”

But when East Maui residents reported seeing the slug, Pang’s two visits failed to produce a specimen.

“They are tiny, the babies could be invisible or just the size of a comma, until they mature, and even then they are only three-quarters of an inch long,” Pang said in a phone interview. “They are different from other slugs, they have a weird greenish-yellow cap on their back.”

He cautioned residents to wear gloves and use tongs to remove them from gardens and yards.

“Don’t squish them,” he said. “You only spread them.”

As a precaution, gardeners should pull all greens and lettuce leaves off at the base instead of cutting them, Pang said.

“My wife has been scrubbing every piece of lettuce under running water, front and back, with a soft brush,” he said. “Then she puts the greens in a mild vinegar solution before a final rinse under running tap water.” 

How safe from contamination are tomatoes, cucumbers and other Hawaii-grown vegetables?

“Slugs like to hide in moist, confined spaces,” Pang said. “Even the mucus in a slug’s slime trail can carry the disease.”

Along with using slug bait pellets, Cowie advised residents to “make sure everything is neat and tidy around and under your house, no piles of thrown-away cardboard or sheets of plastic. Slugs like to be out of the wind, out of the sun.”

Thoroughly cooking food at least three to five minutes, or freezing it at 5 degrees Fahrenheit for at least 24 hours, will kill the larval stage of the worms, health experts say.

A Cure Has Not Been Found

Humans become infected when we absorb the rat lungworm larvae by ingesting food contaminated by affected slugs and snails. Symptoms can include severe headaches, neck stiffness, skin sensitivity, fever, nausea, paralysis, light sensitivity and tremors.

The only diagnostic test must be performed by the State Laboratories Division on cerebrospinal fluid extracted through lumbar puncture. There is no cure, only palliative care with pain medication, antibiotics and possibly steroids.

Cowie gathered an international group of scientists in Honolulu in 2011 to establish guidelines to deal with rat lungworm on “a global scale.”  Experts from as far away as Brazil, China, Thailand and Jamaica identified priorities to protect food, and diagnosing and treating the disease’s victims.

Robert Cowie has researched slugs and snails in many parts of the world. He’s pictured here in Brazil. Courtesy of Robert Cowie

Along with health officials and disease researchers, Cowie testified at a joint Senate and House briefing at the state Capitol on Feb. 22 as lawmakers debated whether to spend more money on rat lungworm research and to educate us about how to protect ourselves. Senate Bill 272 is under consideration, but no funding is currently attached.

As politicians talk and health officials fret, potentially deadly slugs on three of our islands continue to multiply and most of us are unaware of an infectious danger in some yards and parks where we picnic, play with our kids and seek respite from the cares of daily life.

“I go out in my yard every night gathering up slugs, usually four a night but if I am not home for a few days I likely get 40 or more,” Cowie said.

“I know we can’t eradicate the slugs or snails or rats. We have to reduce the possibility of people interacting with the them, make sure people know how to clean produce so they don’t inadvertently eat a slug or snail. There’s always a chance a very small translucent one is missed. I think that’s the most likely way people are getting infected. Also through water. Slugs and snails fall into water and drown, then release the worms in the water.”

Cowie warned that anyone with a water catchment system should keep the tank cover “sealed tight. These things are a pain but it is possible to do them to minimize human exposure. Birds, cows, pigs, horses and dogs can get rat lungworm too.”

My two Maui friends who have rat lungworm disease are enduring, as one put it, “unimaginable pain and suffering.” Their recovery time and ultimate prognosis are uncertain, as is the case with every victim, medical experts say.

The constant presence of lungworm-hosting rats and ideal carrier slugs means that more Hawaii residents could be vulnerable to a potentially fatal disease.

“It only takes a day to go from ingestion of larvae for the disease to travel to the brain,” Cowie said. “Worms develop in the brain, grow bigger and start moving around in the brain, looking for a way out. When they do finally die there is an immense reaction in the brain. Some people never fully recover.”

About the Author