Nearly 1 in 4 rats sampled in Florida tested positive for it.
In the study, researchers examined 171 rats, 37 rat fecal samples, and 1,437 snails and slugs throughout Florida.
They discovered that 23 percent of rats, 16 percent of rat fecal samples, and two percent of snails and slugs tested positive for the rat lungworm parasite.
That can be a problem for human health. The adult form of the parasite is present only in rodents, but they pass the larvae on through their poop.
Snails and slugs then ingest the larvae. The problem for humans comes in if they eat raw or undercooked snails or slugs, or if they eat raw produce like lettuce that contains slug remnants, according to the Centers for Disease Control and Prevention (CDC).
The larva develops in the human host, until they reach a near-adult stage in your brain, researchers from the University of Hawaii explain. (Sometimes, the worms can migrate to your lungs, and have even appeared in the eyes.)
The infection is a major cause of eosinophilic meningitis, which can cause anything from a mild headache to severe headache, neck stiffness, neurological problems, coma, or even death.
In most cases, though, people fully recover, even without treatment.
Rat lungworm has historically been a subtropical parasite—it’s been endemic in Hawaii—and its ability to survive in more temperate Florida areas is alarming, the researchers write.
“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,” study author Heather Stockdale Walden, Ph.D., said in a statement.
As the climate continues to change and the average temperatures begin to rise, it’s likely that the parasite’s distribution will probably expand, leading to its spread in even more temperate areas, the authors write in the study.
So what can you do to avoid ingesting the worm? You may want to avoid eating snails, or raw or undercooked frogs or crustaceans, which can also spread the worm.
And be sure to wash fresh produce thoroughly, and to wash your hands well after handling snails or slugs, Stockdale Walden explained.