KAILUA-KONA — Two years ago, no one could find a trace of the semi-slug in North Kohala.
But today, the vector non grata believed to be the most effective and efficient distributor of rat lungworm disease (RLW) on Hawaii Island appears well established throughout the district.
Staff from the Daniel K. Inouye College of Pharmacy at the University of Hawaii-Hilo (UHH) confirmed the presence of the semi-slug in the district following a slug and snail hunt by a handful of sixth-graders at Kohala Middle School.
The youngsters were led by their science teacher, Cristy Athan, who took a professional development class on RLW identification and eradication through the Hawaii Community Foundation’s Career Connected Learning STEM grant. She said she was drawn to the course because of its element of citizen science and the impact that can have on a community.
“We were the first to identify the semi-slug in North Kohala,” Athan said. “It seems to be well established here.”
What her students accomplished in their identification of the vector may end up meaning a great deal, not just to farmers and home gardeners in the area, but also to the health safety of residents across the district.
Known scientifically as Parmarion martensi, researchers are certain the semi-slug carries a higher concentration of RLW parasites than any other vector, with one slug capable of hosting several thousand parasites at any one time.
The working theory coming out of UHH research is the load potential of a semi-slug increases the likelihood of more severe symptoms of RLW if it infects someone, including permanent disability or even death. Less serious instances leave no lasting damage in humans.
“There is some idea that there could be that relationship between parasite load and intensity or severity of disease,” said Franny Brewer, communications director with the Big Island Invasive Species Council (BIISC).
While a lack of research funding has limited what specialists know about RLW and its vectors, there does appear to be a correlation between the introduction of semi-slugs to Hawaii Island and a spike in the intensity of the disease.
RLW has been around at least since the 1960s and possibly for as long as 100 years, Brewer explained. But the disease severity spiked in the mid-to-late-1990s when semi-slugs, an invasive species, arrived on the island.
Other reasons BIISC and UHH researchers believe semi-slugs to be the most dangerous of RLW vectors is their behavior, Brewer continued.
Attracted to plastics, semi-slugs hide in pop-up tents and trash cans. They’re also commonly found in potted plants.
More than that, the slugs are speedy, which almost sounds like an oxymoron. Brewer has heard stories of people at a picnic table putting down their glasses, walking away for a brief time, and returning to find a slug in the liquid.
While most slugs and snails frequent gardens, Brewer finds slugs on her steps, her porch and frequently inside her Puna home.
“Semi-slugs — their behavior seems to really bring them around people and their stuff,” she said.
It was the semi-slugs’ behavior and how quickly they migrated and established from lower-Puna to upper-Puna that grabbed the interest and concern of Kay Howe, a part of the RLW research team at UHH.
Brewer said Howe’s initial fear was the semi-slug may have migrated to Waimea and could create an impact through extensive agricultural production there. That, in part, inspired the professional development course Athan signed up for, along with 16-18 other teachers.
As of yet, the presence of semi-slugs in Waimea remains unconfirmed, the vectors seemingly leap-frogging the area and landing in North Kona above.
While there’s no way to know for certain, Brewer said she and Howe believe temporary displacement of hundreds of people caused by the Kilauea eruption in May could be a primary catalyst behind the semi-slug migration.
Whatever the reason, there’s cause for concern the potent vector population may find its way to points south throughout West Hawaii.
“It being in Kohala brings it so much closer, and that’s nerve wracking having seen how quickly it moved around the island in the last 10 years,” Brewer said. “It’s moved very fast, and so we’re very nervous about Waimea.”
Athan said the 60-some students who’ve participated in the snail and slug hunts around the Kohala Middle School campus were apprehensive themselves about coming into contact with semi-slugs, at least at first.
But when disposal is conducted safely using slug/snail baits or gloves, disposable chopsticks and containers with one part salt and seven parts water — a.k.a. a slug jug — most students abandoned their fear for curiosity.
“There’s always that ‘ick’ factor, but they soon got over it,” Athan said. “They’re so curious now about this whole project we’re doing. They come up with so many questions.”
Athan added she plans to continue the program in coming years. Students will also join her at a booth during the Kohala Jamboree at Kohala High School to showcase what they’ve accomplished and raise community awareness about the newly established semi-slug.
For those interested in attending, the jamboree runs from 9 a.m. to 2 p.m. on March 2.
Brewer said it’s crucial that everyone in the North Kohala community and across the island learn methods to identify and dispose of semi-slugs in the interest of public health. The same methods can be employed to deal with other snails and slugs because as far as research indicates, every type of each is a potential carrier of RLW.
“If people don’t know it’s in the area, it’s one of those things people think, ‘Oh, that’s an east side problem or a Hilo problem or a Puna problem,” Brewer said. “I think there’s a tendency in all of us to think there are dangers out there, but (that we’re) safe. ‘It’s not going to effect me.’ That’s how our minds work. We go into denial.”
Brewer added two bills currently moving through the state Legislature this session, which are supported by BIISC and will help fight invasive species and enhance biosecurity, are Senate Bill 523 and Senate Bill 1140.
She encouraged those concerned to visit the Hawaii State Legislature’s website at www.capitol.hawaii.gov to read up on the bills and submit testimony in support of them.