Confirmed Detection of Rat Lungworm Vector in Kohala District

Staff from the University of Hawai‘i-Hilo Daniel K. Inouye College of Pharmacy (DKICP) confirmed a collection of Parmarion martensi, an invasive slug, from the Kohala District of the Big Island. Inquiries of local residents further revealed multiple sightings in the area, indicating that this invasive pest has established in the Kohala District of the Big Island.

Rat lungworm disease is carried by slugs and snails. PC: Hawai‘i Department of Health

It is commonly called the “semi-slug” for the partially formed shell on its back. It has been associated with increased incidences of Angiostrongylus, or rat lungworm disease (RLWD). The parasite, Angiostrongylus cantonensis, infects rats and snails or slugs at different times during its life cycle.””

Humans can contract the disease after accidentally consuming the parasite from a slug or snail. Cases range from severe discomfort and illness to permanent disability or even death, depending on the amount of microscopic parasites consumed.

Although all snails and slugs can carry the infective form of the parasite, semi-slugs are effective hosts with a high percentage of infection and can be heavily infected, said Kay Howe, DKICP education coordinator at UHH,

“They have unusual behavior in that they like to be around human dwellings, are good climbers and are relatively fast,” said Howe. “Research at the DKICP has also shown the semi-slug can shed the rat lungworm parasite if drowned in water, such as in a catchment tank or uncovered beverage.”

The presence of the slug was confirmed through the efforts of students at Kohala Middle School, who are participating in a citizen science effort led by teacher Cristy Athan. Athan enrolled in a professional development class offered by UHH-DKICP and the Big Island Invasive Species Committee to learn more about rat lungworm and invasive rats and slugs. Teachers are taught safe handling protocols for the collection and disposal of snails and slugs, and are guided to develop an Integrated Pest Management Strategy to reduce slug and snail populations in school gardens. The students embraced the project and have enthusiastically committed to their roles as ambassadors for RLWD prevention.

“They’re so into it,” said Athan. “Every single day, they’re telling me a new slug or snail story!” Funded by the Hawai‘i Community Foundation’s Career Connected Learning STEM grant, the teacher professional development class offers standards-aligned lessons for teachers to use in their classrooms to increase awareness and safety in their school and at home, and to contribute to ongoing scientific efforts to develop a better understanding of slug/snail behavior.

Howe was inspired to create the curriculum after her son contracted a serious case of the disease in 2008. Although she had worked at a school garden in Waimea the year before, she had never heard of RLWD. Over the years of supporting residents and visitors who contracted RLWD, Howe often heard a similar sentiment: before diagnosis, many of them had never heard of it.

“I was concerned because my mind kept coming back to that school garden,” said Howe. “As school gardens were being put in at schools across the island, I was so excited for the opportunity for the students to learn about agriculture and growing their own nutritious food, but I also worried—what are they doing about rat lungworm? Do they even understand the risk?”

“We have not yet found the semi slug in Waimea,” Howe said. “The species I am referring to is the European garden snail Cornu aspersum. We do know that this slug has been working its way up-elevation on the Hilo side and is now up to Mt. View and possibly beyond. North Kohala should be vigilant as should Waimea, as these slugs make it to new locations usually via people transporting things. Waimea people should be on the lookout for it.”

Residents of Kohala are asked to be vigilant for this slug and to be extremely careful with washing garden vegetables. Slugs or snails should never be collected with bare hands—gloves or chopsticks can be used to dispose of slugs in heavily salted water. Slug baits can reduce populations around gardens and yards. Resources on RLWD and on the teacher training can be found online.