Rat lungworm More Common In U.S. Than People Think, CDC says

by Kim Boateng Posted on August 3rd, 2018

‎Atlanta, Georgia, USA:  A parasite called rat lungworm, which can get into people’s brains, has infected 12 people including toddlers in the continental U.S. in recent years, federal health officials said Thursday.

And more cases may have gone unreported, because the parasite often does not cause severe symptoms, and it’s been found across several states.

Rat lungworm made headlines last month after it infected two people in China who ate raw centipedes, but people living in the U.S. might catch it by eating snails or vegetables out of home gardens, the Centers for Disease Control and Prevention said.

Several of the infected are very young children, said Dr. Sue Montgomery, a senior epidemiologist at the CDC’s parasitic diseases branch who led the research team.

“They have a history of crawling around outside,” Montgomery said.

At least one of the infected children was known to eat dirt, and the children are likely to have accidentally eaten snails or slugs, she said.

Some of the affected adults said they had eaten fresh vegetables. “Some of the fresh produce had been grown in the backyard,” Montgomery said. “They probably inadvertently ate a snail or slug.”

Undercooked shellfish are another possible source of infection.

Travelers can catch the parasite, which originates in rats. Six of the cases identified by the CDC since 2011 were in people living in the southern U.S., including Texas, Tennessee and Alabama, the CDC said. The rest were in travelers who may have eaten the parasite overseas.

The CDC count does not include 18 cases reported in 2017 by the state health director of Hawaii, where the parasite is already a well-known risk.

Rat lungworm is a nematode whose scientific name is Angiostrongylus cantonensis. It has a stomach-churning life cycle that starts in rats.

“Their normal route in the rat is that they are ingested, they penetrate the intestine and they make their way to the brain, where they develop,” said Heather Stockdale Walden, a parasitologist at the University of Florida who has studied the worm.

“They come back to the pulmonary artery in the rat and they reproduce.” Rats excrete it and it can get picked up by snails and slugs, some of which are very tiny. The CDC explains its life cycle in a video.

“In humans or horse or dog or bird it’ll still penetrate the intestine and it’ll enter the circulation and go to the brain and that’s where it stops. It doesn’t finish its development into the worm,” Walden said in a telephone interview.

Walden led a survey last year that found the parasite all over Florida.

“We sampled snails. We sampled rats. We even collected rat feces off the ground, and we looked for the parasite and we found it in Florida from Miami to the Panhandle,” she said.

“It is definitely there,” she added. “We found it in invasive species of snails and we also found it in the native snails here in Florida.”

Because the parasite thrives in warm weather, it is likely to become more common further north as the climate warms, she said.

It does not always cause symptoms in people, but when it does, it often causes a severe headache. When the parasite reaches the brain, it can cause meningitis, an inflammation of the membrane surrounding the spinal cord.

It also causes production of immune cells called eosinophils, which spill into the spinal fluid.

“It all depends on the number of parasites in there,” Walden said.

“Clinical signs of infection in adults include headache, stiff neck, fever, vomiting, nausea and paralysis of the face and limbs. The most common symptoms of infection in children are nausea, vomiting and fever,” the CDC said.

The CDC issued the report Thursday to remind doctors to consider the possibility of rat lungworm infection in people who have eosinophilic meningitis.

It’s rarely fatal and usually gets better on its own, although the meningitis can cause long-lasting neurological symptoms such as weakness or shaking. One of the 12 patients the CDC studied developed seizures.

The CDC’s advice: Don’t eat raw slugs or snails. Hawaii’s health department also warns against drinking water out of hoses, because snails can crawl inside them.

“Be sure to thoroughly wash any produce or raw vegetables before you eat them,” Montgomery advised.

And watch out for silly kid tricks.

“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 two weeks, without treatment of the infection,” the CDC says.

What is Angiostrongylus cantonensis? – CDC

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 angiostrongylus cantonensis parasite?

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

How can people get infected with angiostrongylus cantonensis parasite?

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.

Learn more about how people get infected with Angiostrongylus cantonensis in this new motion graphic video.

Can an infected person infect other people?


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 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 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.


Kim Boateng

Kim Boateng

Staff Writer

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