Rat Lungworm Disease: Optimism Comes with Education By Stefan Verbano
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KeOlaMagazine.com | March - April 2020
nside garden hoses, along the walls of rain catchment tanks, between the folds of lettuce leaves, the slugs and snails slither. Although they look just like their harmless mainland cousins, these Hawaiian gastropods harbor a strange and potentially life-threatening parasite known as the rat lungworm. On Hawai‘i Island, where residents and visitors alike battle fire ants, mosquitoes, coqui frogs, and giant cockroaches, the common slug and snail species found chomping on leafy greens or crawling across water tanks may seem like mild tropical nuisances; however, accidentally eat an infected baby slug hidden in a salad, gulp down a kale smoothie with a tiny piece of infected snail inside, or drink untreated catchment water that’s been contaminated with rat lungworm, and it’s possible to contract a disease which causes extreme pain, disability, paralysis, coma—even death. The lifecycle of the parasite reaches its adult stage in the lungs of rats, hence the disease’s name. Rats excrete the worms’ offspring (larvae) in their feces, which is consumed by “intermediate hosts” such as slugs, snails, and flatworms, causing their infection. After rats eat the infected slugs and snails, the parasite’s lifecycle completes when the worms again mature in the rat’s lungs. The parasite infestation of local rats plays a crucial role in the severity of rat lungworm infection in successive hosts. A study conducted on Hawai‘i Island in 2017 tested more than 500 rats collected in and around Hilo. It found rat lungworm in 94 percent of specimens. As the natural reservoir for the parasite, these rats, with their extremely high infection rates, are driving up the population of highly infectious intermediate hosts on the island. The parasites came to Hawai‘i in the early 1960s when the first reports of rat lungworm-infected animal hosts appeared on O‘ahu, spreading from there to Maui, Kaua‘i, and Hawai‘i Island. Two decades ago the disease was distributed much more evenly across the islands. The introduction of a new species of semi-slug called P. martensi to East Hawai‘i right after the turn of the millennium seems to have caused a spike in cases of rat lungworm disease, with the Puna District as the disease’s epicenter. In Puna, highly infectious rats pass parasites to the newly introduced semi-slugs, which tend to carry a higher parasite load than other commonlyfound gastropods, making them more infectious. To make matters worse, the burgeoning semi-slug is unusually active; researchers have witnessed it climb up walls, across hot pavement, and into uncovered beverage cups. There are other Hawai‘i Island animal vectors besides snails, slugs, and flatworms that could potentially cause the 36 disease in humans if consumed raw or undercooked. Infected freshwater prawns, shrimp, ‘opihi (Hawaiian limpet mollusk),
and land crabs have all been documented, in addition to frogs, centipedes, and monitor lizards. Due to its sensitivity to salt, the parasite only infects freshwater aquatic species, rendering Hawai‘i’s popular raw fish dishes like poke safe from rat lungworm. All of this scientific information about the disease—from parasite loads to species vectors—is obtained through the diligent and tireless effort of people committed to fighting rat lungworm’s spread. Pharmaceutical sciences Professor Susan Jarvi, at the University of Hawai‘i-Hilo’s Daniel K. Inouye College of Pharmacy, is one of those people. Her team of researchers is developing blood-based DNA tests to aid in rapid rat lungworm disease diagnosis, testing various antiparasitic drugs’ efficacy against the worms, trialing 40 different vegetable wash solutions, and studying the parasite killing potential of riboflavin and ultraviolet light. Jarvi lab members are also working to detect the infection in various species of domesticated animals. “Weʻre working with veterinarians,” Susan says. “When they get a pet that’s suspected of having rat lungworm, they send us blood samples to test.” Without consumption by any other animals, the rat-slugrat lifecycle of the parasite would go on indefinitely. Humans are what researchers call “dead-end hosts.” The worms are ill-adapted to complete their lifecycle in the human body so they rarely make it to the lungs and end up dying without intervention along the way. Their dead and decomposing bodies cause the severe inflammation responsible for many of the disease’s symptoms. When a human eats or drinks food or water infected with rat lungworm, the parasites survive the acidity of the stomach and travel through the intestinal walls and various organs on their way to the spine and central nervous system. Worms enter the brain/spinal cord and can cause severe meningitis— inflammation of the three protective membranes called “meninges” lining the skull and vertebral canal that enclose and protect the brain/spinal cord. Graham’s Story Just after Christmas in 2008, Kathleen “Kay” Howe’s son Graham got sick. He was 23 years old at the time, and had been living on a Kapoho Farm Lots property in East Hawai‘i, eating homegrown produce and staying in a cabin that, Kay says, “didnʻt have a good plumbing system.” After developing a severe headache, stomach pain, muscle and joint pain, and after two futile visits to the Hilo Medical Center emergency room, Graham was finally admitted because he was no longer able to urinate. Kay was overseas working at the time, and had to hear updates on her son’s deteriorating condition via phone before she could get to his bedside.