A parasitic worm that lives in the hearts of rats and is transmitted to humans via an invasive slug from Southeast Asia is to blame for several people in Hawaii coming down with a rare form of menengitis, an infection of the  cerebral-spinal fluid.  Several people in Hawaii have reported severe symptoms from the parasite requiring hospitalization. Two of them remain in a coma in a Hilo hospital. 

Big island residents are cautioned to avoid eating slugs and snails and  to take care in the washing and preparation of garden greens in areas affected by rats, slugs and snails.

Rat lungworm is a tropical disease found in warm, moist climes that is caused by Angiostrongylus cantonensis, a parasitic worm carried by rats. The rat lungworm parasites live in the pulmonary arteries of rats, much in the same way that dogs in Hawaii are affected with heartworm.  However canine heartworm Dirofilaria immitus does not affect humans The heartworm life cycle begins when a dog with circulating microfilaria in its bloodstream is bitten by a mosquito whereas the rats excrete worm larvae in their feces, which are sometimes eaten by small snails and slugs that reside in the folds of lettuce, peppers and other produce.

Disease cycle: The mature (adult) form of the parasite is found only in rodents (it is not found in people). Infected rats pass immature forms (larvae) of the parasite in their feces. Snails and slugs get infected by ingesting the larvae in rat feces. These larvae mature in snails and slugs but do not become adult worms. The life cycle comes full circle when rats eat infected snails or slugs and the larvae further mature to become adult worms.

Symptoms: After ingesting the worm larvae, people report symptoms including severe headache, stiff neck, tingling or painful feelings in the skin, low-grade fever, nausea, and vomiting, according to the Centers for Disease Control and Prevention (CDC). "There have been documented deaths but they are very rare," says Sarah Park, the state epidemiologist for Hawaii. The severity of the illness seems to depend on how many worms are ingested, how strong a person's immune system happens to be, and how long the worm stays in the  cerbral spinal fluid  she notes, adding that it in some cases worms have survived for up to several months. 

However, rare cases of eosinophilic meningitis  can cause serious and permanent damage to the brain and nervous system. "We don't know about all the cases out there," because there is no diagnostic test for the disease, Park told ScientificAmerican.com, saying that diagnoses are made based on clinical observations, suspicion of exposure to the parasite, and the presence of elevated levels of eosinophils, (white blood cells) in the cerebrospinal fluid that might indicate a parasitic infection.

Recently two people from the Puna district  reported experiencing "agonizing pain" after eating a salad  which may have contained slug hidden inside folds of raw peppers. Physicians at Hilo Medical Center on the Big Island of Hawaii reportedly discharged the patients several times before finally admitting them in mid-December, One is now recovering, the other remains in a coma at HMC.

"Many different species of slugs and snails are known to be carriers of this particular nemotode [rat lungworm parasite]," Robert Hollingsworth, an entomologist at the U.S. Pacific Basin Agricultural Research Center in Hilo told ScientificAmerican.com.  African land snails are also known to carry the disease. When people ingest the worm, it travels from the gastrointestinal tract to the  central nervous system. Most people experience no symptoms or only mild ones such as muscle aches and sensitivity to light and recover without treatment, in most cases without ever suspecting a parasitic invasion. The worm typically dies off in a few weeks.

On the rise: The prevalence of rat lungworm disease may be on the rise after an invasive slug species from Southeast Asia, Parmarion martensi, arrived in Hawaii in 2004 and began out-competing the Cuban slug, Veronicella cubensis, one of the most common large slug species in Hawaii.According to a study co-authored by Hollingsworth and published in the journal Pacific Science in 2007 suggests that Researchers found that 77.5 percent of the invasive species were carrying the rat lungworm parasite compared to 24.3 percent of the Cuban slugs. "The transmission potential of this species may be higher than that of other slugs and snails in Hawaii," the researchers wrote.

People can get infected by eating raw or undercooked snails or slugs that are infected with this parasite. In some cultures, snails are commonly eaten. A child in New Orleans reportedly was infected afater swallowing snails/slugs “on a dare.” People also can get infected by accident, by eating raw produce (such as lettuce) that contains a small snail or slug or part of one. Other ways of getting infected may include eating raw or undercooked freshwater prawns, crabs, or frogs. Of note, fish do not spread this parasite.

The best way to avoid rat lungworm disease? Avoid accidentally eating raw snails or slugs. Be careful around water catchment systems and damp areas where slugs and snails gather especially in the Puna areas of Kehena and Seaview. Irradicate rats that carry many diseases. Don't let compost and fruit droppings attract rats.  Park advises Inspecting and washing fresh vegetables and fruit very well, noting that the slugs and snails are small [as short as 2 mm in length] and can be hidden in creases of vegetables.  The state Health Department also warns that freshwater prawns, crabs or fish and mollusks such as snails should be cooked thoroughly before eating. Note that  heat kills the parasites — recommend boiling or steaming 3-5 minutes, .

Does Rat Lungworm usually require hospitilization?  Usually not. The parasite dies over time, even without treatment. Even people who develop eosinophilic meningitis usually don't need antibiotics. Sometimes the symptoms of the infection last for several weeks or months, while the body's immune system responds to the dying parasites. The most common types of treatment are for the symptoms of the infection (such as pain medication for headache) rather than for the infection itself.

For more information call the East Hawai'i District Health Office at (808) 933-0912 or the West Hawaii District Health Office at (808) 322-4877.

On the Web, more information is also available on the Centers for Disease Control and Prevention site at: www.dpd.cdc.gov/DPDx/HTML/Angiostrongyliasis.htm