A parasitic worm that jumps from rats to snails to the human brain has invaded the United States, researchers warn.
Between 2019 and 2022, a fifth of rats at an Atlanta zoo were found to have rat lungworm.
The beetle can cause severe stomach and nerve problems in humans, including nausea, vomiting, stiff neck and headaches.
The infections in Atlanta suggest there is ongoing transmission in the region, experts said.
Dr. Nicole Gottdenker from the University of Georgia said: “The zoonotic parasite has been introduced and established itself in a new area in the southeastern United States.”
Rat lungworm normally lives in the blood vessels surrounding a rat’s lungs, where it lays eggs.
The larva hatches from the lungs, is coughed up by the rat, then swallowed and excreted as feces before being eaten by slugs or snails.
Rats then eat the snails and the process can begin again.
However, people can accidentally become infected if they eat uncooked snails or shellfish that carry the worms.
In humans, the beetle penetrates directly into the spinal cord and brain.
The illness usually lasts between two weeks and two months, but can last longer and is similar to bacterial meningitis.
Serious complications can occur, rarely leading to nerve damage, paralysis, coma or death.
Cases have already been detected in Hawaii, Florida, Louisiana, Texas, Mississippi, Tennessee and Alabama but have not been sustained.
The latest study, published in the journal Emerging Infectious Diseases, was the first to uncover the parasite in rats in Atlanta.
Researchers collected tissue samples from 33 wild brown rats captured on the zoo grounds.
They detected infection in seven rats: one in 2019, three in 2021 and three in 2022.
Researchers warned doctors to be on the lookout for lungworm infections in patients who appear to have meningitis.
Dr. Gottdenker said: “Understanding the patterns of the lungworm A. cantonensis in North America is critical to reducing the risk to humans.
“Medical and veterinary professionals throughout the southern United States should consider A. cantonensis infection in differential diagnoses.”