Rat Lungworm (Angiostrongylus cantonensis)

Rat lungworm (Angiostrongylus cantonensis) facts

*Rat lungworm (Angiostrongylus cantonensis) facts written by Charles P. Davis, MD, PhD

• Rat lungworm (Angiostrongylus cantonensis) is a parasite that infects rats with the adult parasitic form found only in rodents. The infected rats pass larvae in their feces to reach slugs and snails. The parasitic life cycle continues in the snails and completes when rats eat infected snails and the larvae develop into worms in the rat. Angiostrongyliasis is the term describing rat lungworm infection of humans.
• People get infected by eating raw or undercooked snails and/or slugs infected with the rat lungworm. Some researchers suggest other freshwater feeders such as shrimp, crabs, or frogs may also carry and transmit the parasite to humans, but fish do not seem to spread this parasite.
• An infected person cannot transmit parasite to others.
• Most infections occur in Asia and the Pacific Islands, but people have reported infections in the Caribbean and Africa. In the U.S., Hawaii reported three infections in tourists in 2019.
• Giant African land snails can be infected with this parasite.
• Although some people infected with rat lungworm may have no symptoms, others may have headaches, stiff neck, paresthesias in the skin, low fever, nausea, and/or vomiting. Rarely, meningitis (eosinophilic meningitis) may develop. It can be fatal.
• Notify your health care provider if you think you might have an infection with the rat lungworm parasite.
• Most rat lungworm infections do not need to be treated as the parasite dies over time. However, most common treatments cover the symptoms such as headache and/or low fevers.
• To avoid getting rat lungworm, do not eat raw or undercooked snails or slugs, and other animals like frogs or shrimp, especially in areas where the parasite is common. In addition, avoid eating uncooked vegetables.

What is Angiostrongylus cantonensis?

Angiostrongylus cantonensis is a parasitic worm of rats. It is also called the rat lungworm. The adult form of the parasite is found only in rodents. Infected rats pass larvae of the parasite in their feces. Snails and slugs get infected by ingesting the larvae. These larvae mature in snails and slugs but do not become adult worms. The life cycle is completed when rats eat infected snails or slugs and the larvae further mature to become adult worms.

Can people get infected with this parasite?

Yes. People can get infected, under unusual circumstances. However, even if infected, most people recover fully without treatment.

How can people get infected?

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. Some children, in particular, have gotten infected by 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.

Certain animals such freshwater shrimp, crabs, or frogs, have been found to be infected with larvae of the parasite. It is possible that eating undercooked or raw animals that are infected could result in people becoming infected, though the evidence for this is not as clear as for eating infected snails and slugs. Of note, fish do not spread this parasite.

Can an infected person infect other people?

No.

In what parts of the world have people become infected with this parasite?

In many parts, but most of the known cases of infection have been in parts of Asia and the Pacific Islands. Some have been in other areas of the world, such as in the Caribbean and Africa.

Have cases of this infection occurred in the United States?

Yes. Cases have occurred in Hawaii (and other Pacific Islands). Very few cases have been reported in the continental United States. In 1993, a boy in New Orleans got infected by swallowing a raw snail “on a dare.” The type of snail he swallowed isn’t known. He became ill a few weeks later, with muscle aches, headache, stiff neck, a slight fever, and vomiting. His symptoms went away in about 2 weeks, without treatment of the infection.

Can giant African land snails be infected with this parasite?

Yes. This type of snail, which can grow larger than a person’s hand, is just one of many types that can be infected. But snails can be infected only if they have ingested contaminated rat feces. We don’t know if any of the giant African land snails in the continental United States are infected.

What are the signs and symptoms of infection with this parasite?

Some infected people don’t have any symptoms — or have only mild symptoms that don’t last very long. Sometimes the infection causes a rare type of meningitis (eosinophilic meningitis). The symptoms can include headache, stiff neck, tingling or painful feelings in the skin, low-grade fever, nausea, and vomiting.

What should I do if I think I might be infected with this parasite?

You should see your health care provider, who will examine you and ask about any symptoms, travel, and exposures you’ve had (for example, to snails/slugs). You might have some blood tests, as well as tests for meningitis.

Does infection with this parasite need to be treated?

Usually not. The parasite dies over time, even without treatment. Even people who develop eosinophilic meningitis usually don’t need antiparasitics. 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 or medications to reduce the body’s reaction to the parasite, rather than for the infection itself. Patients with severe cases of meningitis may benefit from some other types of treatment.

How can I keep from getting infected with this parasite?

Don’t eat raw or undercooked snails or slugs, frogs or shrimp/prawns. If you handle snails or slugs, wear gloves and wash your hands. Always remember to thoroughly wash fresh produce. When travelling in areas where the parasite is common, avoid eating uncooked vegetables.