Ask the Doctors

Dear Doctor: My family is planning a trip to Hawaii in a few months, and we've been hearing about a condition called rat lungworm disease. What is it? And is there anything we can do to prevent infection?

Dear Reader: Rat lungworm, a disease that affects the spinal cord and the brain, is caused by a roundworm known as Angiostrongylus cantonensis. It's a parasite, which means it requires a host to live, grow and reproduce. Although rat lungworm disease is most commonly found in Southeast Asia, the Caribbean and certain tropical Pacific islands, it is now established in Hawaii. So far in 2017, at least nine cases of rat lungworm disease have been reported throughout the state.

As with a number of other previously rare or site-specific diseases, international travel, trade and shipping are playing a role in expanding the parasite's reach. In recent years, the roundworm that causes the disease has also been found in Alabama, Florida, Louisiana and California.

The adult form of the roundworm lives in rats, which excrete the larvae in their stool. When snails and slugs feed on infected rat stool, they become carriers of the parasite. Larvae may also be found in freshwater prawns, crabs, frogs and fish. People become infected when they eat raw or undercooked portions of these foods. Some individuals report becoming infected by eating vegetables, fruit or salad greens that were not properly washed and were contaminated by snails or slugs.

Once the larvae enter the human body, they burrow through the walls of the digestive tract and enter the blood vessels. This eventually brings them to the meninges, the membrane that surrounds the brain and spinal cord. But because humans are not appropriate hosts for this roundworm, the larvae soon die.

It's the presence of these dead larvae in the cerebrospinal fluid that results in harm to humans. They trigger the release of a flood of white blood cells known as eosinophils, one of whose jobs is to attack foreign substances. This outpouring of white blood cells results in severe inflammation known as eosinophilic meningitis.

Symptoms, which can include headache, stiff neck, hypersensitive skin, visual disturbances, fever, nausea and vomiting, vary from person to person. The disease lasts from one week to several months and resolves on its own. In rare cases, it can result in coma or death.

As for what you can do to protect yourself, the state of Hawaii and the Centers for Disease Control and Prevention offer the following advice:

-- Thoroughly wash all salad greens, raw fruit or vegetables under running water.

-- The snails and slugs that carry rat lungworm larvae can be quite small and easy to miss. This means you must wash leafy greens piece by piece, both front and back. Be sure to examine them closely before adding them to a meal.

-- When dining out, ask your server whether all fresh produce is carefully cleaned.

-- If you order freshwater prawns or fish, ask that they be cooked to an internal temperature of at least 165 degrees.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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