Rat lungworm is found currently on Maui, Molokai
UH study finds parasite has not made it to Lanai
Researchers who studied nearly 1,300 snails and slugs across the islands say that rat lungworm could eventually make its way to higher elevations as the climate warms.
Rat lungworm, a parasite that lives inside slugs and snails, was found on five of the six largest Hawaiian Islands — including Maui and Molokai, though not on Lanai — according to a University of Hawaii at Manoa study released Tuesday.
Considered “an emerging infectious disease,” rat lungworm has spread throughout the tropics, including the Hawaiian Islands. A spate of cases in 2017 raised concerns and awareness of the disease, making the study “especially timely,” the college said in a news release.
“Local residents and visitors need to know what the risks are,” said Robert Cowie, senior author of the study and a research professor at the UH-Manoa Pacific Biosciences Research Center. “The data will be important to the state Department of Health in targeting epidemiological surveys and interventions.”
Rats harbor the parasite and pass the larvae along in their feces, which can be ingested by slugs, snails and other animals, such as frogs or freshwater shrimp. Humans can become infected by eating raw or undercooked products that have been contaminated by the parasite.
Hoping to understand where the disease might spread next, researchers in the study screened almost 1,300 snails and slugs representing 37 species from almost 200 sites around the islands.
Rat lungworm tended to occur in warmer and rainier locations, generally — but not exclusively — on the windward side. On Maui, rat lungworm was found in northwest Maui, South Maui, the north shore, Upcountry and East Maui. On Molokai, it was detected in a central part of the island near the forest reserve, and in the East End near Halawa. Researchers tested sites around Lanai City but found no instances of rat lungworm.
“Remember that it is not possible to say that rat lungworm is absent from locations where we did not detect it,” Cowie said. “One can never do a totally comprehensive survey of all snails present in Hawaii, so people must not be complacent and assume, for instance, that based on this study rat lungworm is not in their yards.”
Based on the areas where rat lungworm was found, as well as anticipated climate conditions through the year 2100, researchers found that areas with higher rainfall and temperatures provided ideal habitats for rat lungworm. They predicted rat lungworm will spread to higher elevations, and possibly expand to more temperate regions around the globe.
Cowie said that rat lungworm has “been considered globally as a neglected but emerging infectious disease.”
The disease causes a rare type of meningitis, according to the state Department of Health. Symptoms include severe headaches and stiffness of the neck, tingling or painful feeling in the skin or extremities, low-grade fever, nausea and vomiting. They usually occur one to three weeks after exposure and last two to eight weeks, though it varies by person.
Responding to questions via email Thursday, Cowie said Hawaii researchers first made the connection between snails, the parasite and rat lungworm disease in 1961. Since then, researchers have recorded a total of 123 cases by the end of 2017.
Cowie said Maui County does not “stand out from the rest of the state” in his study, but said that the study was conducted prior to his UH research center confirming the presence of the semi-slug on Maui. He said this species of snail is an especially good host for the parasitic disease and has been associated with the spike in rat lungworm cases in the state last year.
In the first three months of 2017, Maui recorded six cases of rat lungworm disease; the island had seen only two recorded cases over the past decade. Statewide, there were 18 reported cases in 2017, a large number on Hawaii island.
Maui’s first, and so far only, case reported this year occurred in mid-February when a person became ill and was briefly hospitalized. The state Department of Health said the infection “likely” occurred on Maui but could not say conclusively because the person had traveled so much.
“A major motivation for my research was to help people to make informed decisions,” said Jaynee Kim, lead author of the study as a UH graduate student and now a malacology researcher at Bishop Museum. “We encourage the public to buy local and support Hawaii’s economy but, at the same time, to be vigilant about washing produce, especially to inspect and wash greens leaf by leaf.
“Buying and planting native plants instead of non-native plants can also help keep invasive snail hosts from being introduced and spread throughout the islands.”
For more information on rat lungworm, visit health.hawaii.gov/docd/disease_listing/rat-lungworm-angiostrongyliasis/.
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