A parasitic worm known to cause a potentially fatal brain infection when it passes from rats to humans has taken hold in the southeastern US.
Researchers from Georgia, Texas, and Mississippi confirmed that dead rats found at an Atlanta zoo had been infected with parasitic A. cantonensis, or lungworm, at least as early as 2019.
Lungworm is typically native to Asia and the Pacific Islands but has been steadily migrating to the West thanks to international travel, global trade, and a changing climate that makes new locations more livable.
Infections from rats to humans are rare but not unheard of. Six human cases were detected from 2011 to 2017 in several southern states as well as Hawaii, where it made headlines after 10 visitors caught it in 2018 alone.
The 33 dead rats tested between 2019 and 2022 were collected from Zoo Atlanta in Georgia
Rats become infected when they eat snails and slugs harboring the worm larvae. Once the rats ingest it, the parasite worms its way through their body and into the central nervous system. The parasite releases eggs in the rat’s lung artery and then travel through the bloodstream, only to be passed in rat feces
Rat lungworm is a parasite that can be transmitted to humans if they eat raw slugs or snails. Seven of the 33 dead rats at the Atlanta zoo had the parasite in their lung, brain, and heart tissue
The parasite’s natural life cycle begins and ends with rodents which become infected when they eat snails and slugs harboring the worm larvae.
Humans are most likely to become infected when they eat those infected slugs or vegetables covered in slug slime, but cannot spread it to another human.
Most people who become infected with lungworm will recover without medical treatment.
But if the worm infects a human and then travels to the brain, it can lead to a rare case of eosinophilic meningitis caused by inflammation of the membranes that cover the brain and spinal cord.
From 2019 to 2022, veterinarians from the University of Georgia, Texas A&M University, Mississippi State University, and Zoo Atlanta in Georgia’s capital conducted testing on 33 dead brown rats found on zoo grounds.
Specifically, they examined tissue from the dead rats’ brains, hearts, livers, kidneys, lungs, spleens, skeletal muscles, skin, gastrointestinal tracts, adrenal glands, and gonads.
Seven of the rats had worms, or nematodes as researchers refer to them, in their heart, lung artery, and brain tissues.
Of that seven, four were confirmed to be infected with lungworm. The three remaining were not confirmed to have lungworm but researchers noted that they had worms in their blood vessels that were consistent with A. cantonensis.
Lungworm had been detected previously in rats in Florida and Alabama, which led researchers to believe that lungworm was likely present in Georgia well before the first dead rats were examined in 2019.
There had also been at least six cases of the parasite found in humans over a span of six years across the southeast.
The researchers said: ‘Discovery of autochthonous cases of A. cantonensis infection in definitive host rodents collected during 2019–2022 in the state of Georgia, suggests that this zoonotic parasite was introduced to and has become established in a new area of the southeastern United States.’
Their findings were published in the CDC’s journal Emerging Infectious Diseases.
Four confirmed infections with the brain-infecting parasite served as an alarm bell for epidemiologists who have been tracking the spread of diseases from their places of origin to far-flung locales such as the United States.
As the global climate continues to warm, more places will begin to feel like the lungworm’s native Southeast Asia, making more places such as the southeastern US a suitable living environment.
A prolonged warm season also means a longer time for the parasite to flourish and infect more species.
Lungworm got its name from the characteristic way in which it exploits the rat host’s own respiratory system to grow.
The parasite’s life cycle begins when eggs are passed in a rat’s feces and hatch in the environment into what researchers call first-stage larvae or L1.
Snails and slugs then gobble up the larvae in the environment when they feed. In the snail’s digestive system, the larvae enter its second stage of life. When it reaches the third stage of development, it has gained the capacity to infect other hosts, including humans.
A mammal, such as the common brown rats found at Zoo Atlanta, eats that infected snail, and the third-stage larvae travel from the rat’s digestive tract to the lungs where eggs are released and circulate through the bloodstream.
Humans who eat the infected snails or slugs, often on a dare according to the CDC, are more likely to become infected, but they are not guaranteed to experience any symptoms.
They may first experience nausea and vomiting a few hours to a few days after eating a contaminated snail. There is no designated treatment for lungworm and it typically resolves on its own.
Neurological symptoms such as headache, stiff neck, tingling or pins and needles feelings in the extremities, and sensitivity to light may follow.
Eosinophilic meningitis as a result of lungworm infection is rare with only about 3,000 documented cases globally since 1944. This could be an undercount, though, as many cases may go undiagnosed or untreated.