Rat Lungworm

Unraveling Rat Lungworm Disease

Writer Rosannah Gosser
Photo Courtesy of Jarvi Labs

A species of nematode is creeping through the Hawaiian islands, creating significant threats to the state’s agriculture and health. Rat lungworm (Angiostrongylus cantonensis) is a parasite that develops between rats, snugs, and snails, and when ingested by a human, it can be deadly. The University of Hawaiʻi at Hilo’s Daniel K. Inouye College of Pharmacy is conducting research on how to best prevent the spread of rat lungworm disease, and a proposed legislative bill may soon permit more funding for research.

The Hawaii-Tribune Herald reported more than 70 cases of rat lungworm disease in Hawaiʻi between 2001 and 2014, and in 2017 there were at least 11 cases just on Hawaiʻi island. Symptoms of rat lungworm disease include headache, fever, and itchy or tingly skin, and in severe cases, inflammation of the brain and spinal cord can lead to paralysis, coma, and death.

The life cycle of the rat lungworm nematode is a unique, albeit complicated, one that begins when a microscopic worm reproduces inside rats and travels through their digestive tract. When expelled through rats’ feces, the parasite will infect slugs or snails that come into contact with it. The larvae then develop inside the digestive tract of slugs or snails, but since slugs and snails are part of a rat’s diet, they can be ingested back into rats.

Once back inside the rat’s digestive tract, the nematode can grow to be macroscopic, or perceived with the naked eye, and will reproduce to begin the life cycle over again, damaging the rat’s central nervous system in the meantime. If spread to an accidental host, such as a human, the parasite may cause similar central nervous system damage and inflammation of the brain.

Most cases of rat lungworm disease in Hawaiʻi have been contracted from people consuming raw produce, especially leafy greens, contaminated by infected slugs or snails. Using or drinking water from catchment systems that have been contaminated by the parasite may also cause the disease, but more research is needed to determine the extent to which this is happening.

In East Hawaiʻi, about 94% of the rat population is infected with rat lungworm, according to Dr. Susan Jarvi of the Hawaiʻi Island Rat Lungworm Working Group. Jarvi attributes the spread of rat lungworm over the past decade and a half in Hawaiʻi to the introduction of the semi-slug (Parmarion martensi), an invasive species of slug with a partially embedded shell on its back. Semi-slugs are adept climbers and move at a faster rate than regular slugs and snails; therefore, they transmit rat lungworm larvae to rat populations, as well as other slugs and snails, more rapidly.

Because of the particular severity of the disease, the extent to which it has spread, and the increase in the number of cases over the past several years, most local farms, restaurants, and markets in the area remain vigilant about IPM, or integrative pest management, in order to provide the community with safe produce. IPM can include using pesticides and growing plants on raised beds or in covered greenhouses.

The Locavore Store in downtown Hilo, which sells locally-sourced produce and other goods, is one of many East Hawaiʻi establishments that takes special care to make sure the produce they sell to consumers is free of contamination. “We try to only work with vendors who use preventative measures in the field, coupled with regular inspections during harvest,” explained Catarina, who co-owns the store with her husband, Arthur.

“The worst answer a farm can give us is that they don’t have slugs,” Catarina said, describing how it’s virtually impossible to stay slug-free in Hawaiʻi’s wet and tropical climate and that this is often a red flag that the farm is not using preventative measures against the spread of rat lungworm.

Although most of the greens at the Locavore Store are not washed on-site, each bag is inspected before being put on the floor. If a slug or snail, sometimes no bigger than a speck of dirt, or even a trail of slime is discovered on the produce, the entire batch is thrown out and the farm from which it was grown is notified. “We’ve been encouraged by the increase in customers and the general public wanting to know about what our farms practice and what they can do as consumers,” Catarina told Ke Kalahea, emphasizing that the most important way people can make sure their produce is safe is by diligently washing and inspecting it themselves.

At UH Hilo’s Daniel K. Inouye College of Pharmacy, Dr. Susan Jarvi has helped develop the Hawaiʻi Island Rat Lungworm Working Group to cultivate educational awareness of the disease and to involve students in the search for solutions. The organization’s curriculum currently works with five schools in East Hawaiʻi and incorporates student observation of slug and snail behavior, as well as experimentation with new methods of IPM.

Dr. Jarvi and her colleagues’ research focuses on developing a blood-based diagnostic to be able to determine cases of rat lungworm more efficiently than the current technique of testing patients’ cerebral spinal fluid. Their research is also looking at anti-parasitic drugs and improving filters in water catchment systems.

“Our study is showing that we need more research,” explained Jarvi. “There must be a better solution to actually kill larvae, but we’ve been able to show that they can live outside of their host in a moist environment for weeks. We hope to get funding to be able to do a study to see if there are any commercially available washing methods that would kill larvae.”

A proposal for $1,000,000 to extend research on rat lungworm disease was introduced by state Rep. Chris Todd, D-Hilo, for the fiscal year 2018-2019, according to the Hawaiʻi Tribune-Herald. Maile Lavea, Treasurer of the University of Hawaiʻi at Hilo Student Association, explained the proposed bill.

“Generally, the purpose of this legislative measure is to appropriate funds to the University of Hawaiʻi at Hilo for programs, studies, and activities related to the prevention and eradication of rat lungworm disease. This measure requires that the University of Hawaiʻi at Hilo submit a comprehensive plan to the Legislature before the appropriated funds are released. The legislation is currently sitting in the House Committee of Higher Education.”

Additional funding for rat lungworm research would allow the Hawaiʻi Island Rat Lungworm Working Group to hire more people studying the transmission of the disease, the nature of the parasite, and IPM techniques in the field. It would also allow for access to better equipment, such as water catchment filters and UV lighting to test its effect on killing larvae. Additionally, the bill proposes commercially available produce washes that would ensure community members have access to clean water.

“It would be great if we could tell people what to wash their vegetables in,” Dr. Jarvi told Ke Kalahea. “That’s an important question that needs to be addressed, and I hope that funding from legislation would be able to answer those questions.We have to better understand the transmission of the disease and why East Hawaiʻi has such high rates of cases. You can’t tell people how to best protect themselves when you’re missing most of the facts, and that’s what research will help solve.”