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Rat Lungworm Parasite Found on Molokai

Black dots show positive rat lungworm test locations, white dots show sample sites. Map courtesy of UH

A recently-released University of Hawaii study has confirmed the presence of rat lungworm on Molokai and on every island throughout the state except Lanai. Rat lungworm is a parasite that has a complicated lifecycle that requires slugs or snails as well as rats to mature. Ingesting a slug or snail infected with the parasite can cause neurological damage, pain and disability, and Hawaii has seen a recent influx of cases of the rare disease.

Researchers tested 11 sites on Molokai starting in 2004 and two sites had a total of four slugs or snails that tested positive for rat lungworm, according to Robert H. Cowie, UH research professor and senior author on the study. The two sites were central Molokai near the forest reserve and east end, near Halawa Valley. Though the study showed limited dispersal of the disease-causing parasite on Molokai, Cowie said it doesn’t mean that it’s not more widespread.

“Non-detection in a particular area does not mean it is absent in that area, just that we did not detect it in our samples,” he said, via email. “And as you can see, we did not do a very broad survey of the island. So it could be more widespread on Molokai than our data show. Nonetheless, just as elsewhere, it is not in every snail/slug.”

Across the state, researchers used molecular techniques to screen almost 1,300 snails and slugs representing 37 species from almost 200 sites on each main island. In general, the study found the spread of rat lungworm to be more prevalent at lower elevation sites with warmer temperatures and higher rainfall. Researchers also developed mathematical models to make predictions on the parasite’s growth under anticipated climate conditions in the year 2100.

“Under these future climate conditions, rat lungworm was predicted to expand its range to higher elevations in Hawaii,” stated a UH release. “The findings imply that the parasite could also expand its primarily tropical and subtropical range globally to regions that are currently more temperate.”
Though rat lungworm disease has existed around for years, the Hawaii cases increased after the invasive semi-slug came to the islands in the early 2000s, according to Department of Health’s District Health Officer Dr. Lorrin Pang, who visited Molokai last year to educate the community on the disease.

According to Pang, the semi-slug is known as the most common type to carry the parasite, but Cowie said the snails or slugs that tested positive on Molokai were of three different species.

Humans can contract the disease by ingesting an infected snail or slug, or its slime. While symptoms generally include extremely painful headaches, Pang said an infected individual won’t notice any symptoms until the parasite has reached the brain — which happens within about 18 hours of eating it. Once in the brain, he said there is no treatment and it cannot be removed but the parasite will die there.

So far this year, there have been five confirmed cases of rat lungworm disease in Hawaii, with a toddler from Hawaii Island contracting it earlier this month.
Experts agree the best prevention is to thoroughly wash all produce before eating it. Pang said to hand rinse each vegetable leaf — soaking in water won’t work. Alternatively, you can “cook the heck out of it, or freeze it for 24 hours.” Pang said boiling for at least three to five minutes will kill the parasite.

“No doubt people are mostly aware of the DoH’s media efforts to inform people that they should thoroughly wash produce, taking special care with leafy greens in which a small snail/slug could easily hide and be missed and then inadvertently eaten,” said Cowie. “All produce, not just local produce, should be washed anyway, as there are other harmful things like bacteria and pesticides that could be on produce regardless of where it came from.”

Experts suggest controlling the snail, slug and rat populations as a way to help prevent the spread of the disease.

“But remember rat lungworm disease is rare, despite the headlines, so there is no need to panic,” added Cowie.


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