A rare parasitic infection has been found in people eight states, several that don't share borders, according to the federal Centers for Disease Control and Prevention, calling into question just how uncommon rat lungworms really are.
Rat lungworm infection, which in extreme cases can cause meningitis in humans, was detected in 16 people between 2011 and 2017 and confirmed in 12, according to a CDC report released Thursday that acknowledged researchers might not have learned about all the rat lungworm illnesses in the continental United States in those six years.
The cases studied came from Alabama, Arizona, California, Colorado, New York, Tennessee, Texas and Utah. And the patients, who included children as young as 1 year old, might have ingested the parasite from their home gardens if they didn't wash their produce well, a CDC official said.
"Some of the fresh produce had been grown in the backyard," said Dr. Sue Montgomery, a senior epidemiologist at the CDC's parasitic diseases branch told NBC News. "They probably inadvertently ate a snail or slug."
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People can become infected not only by eating unwashed produce but also undercooked snails, including ones considered delicacies at restaurants. Other freshwater mollusks or animals that eat snails or slugs, such as frogs, also can transmit the disease to humans.
So cooking snails, freshwater shrimp, crabs and frog legs thoroughly — to an internal temperature of at least 165 degrees — before eating is important.
At least six of the patients reported consuming raw vegetables, two had eaten raw snails, two had eaten prawns, and one ate cooked crab. For two others, "family members reported the presence of snails in the environment," according to the CDC report.
Though human infection often involves no symptoms, rat lungworm can spread to the brain and cause meningitis, neurologic deficits, coma and death.
Most human cases occur in Asia and the Pacific Islands, including Hawaii. But six of the U.S. patients never had traveled outside the continental United States.
The parasite, a type of roundworm, generally lives its life in rats and snails and slugs: A rat eats an infected snail, the parasite migrates to the brain, it develops there, the mature worm travels to its host's pulmonary artery, it reproduces there, a rat then coughs up a worm, the animal swallows it, the rat excretes the immature lungworms in its feces and a snail or slug then crawls through the rat poop.
The snail either eats the excrement or the worms penetrate its soft body, and when a rat eats an infected slug, the life cycle begins again. Humans who happen to become infected can't transmit it to one another.
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The rat lungworm, whose scientific name is Angiostrongylus cantonensis, is different from several species of lungworms that cause respiratory problems in dogs and cats who spend time outside in the woods. Those worms can cause persistent coughing in pets and can be killed with prescription anti-parasite medications, according to the Merck Veterinary Manual.
While Thursday's CDC report looked at rat lungworm problems in humans, University of Florida researchers last year looked at the presence of the parasite in 18 Sunshine State counties from the Panhandle to Miami.
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They found it in five counties.
Rat lungworm "is something that needs to be taken seriously," Heather Stockdale Walden, an assistant professor in the University of Florida's Department of Infectious Diseases and Pathology and the study's lead author, told the Florida Museum of Natural History. "The reality is that it is probably in more counties than we found it in, and it is also probably more prevalent in the Southeastern U.S. than we think."
Contributing: USA TODAY. Follow Natalie Allison on Twitter: @natalie_allison
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