A parasitic worm known to cause a life-threatening brain infection when passed from rats to humans has taken hold in the southeastern United States.
Researchers from Georgia, Texas and Mississippi confirmed that dead rats found at an Atlanta zoo had been infected with parasites. A. cantonensisor lungworm, at least already in 2019.
Lungworm is usually native to Asia and the Pacific Islands, but it has been steadily migrating west thanks to international travel, global trade and a changing climate that makes new places more habitable.
Infections from rats to humans are rare but not unheard of. Six human cases were detected between 2011 and 2017 in several southern states, as well as in Hawaii, where it made headlines after 10 visitors contracted it in 2018 alone.
The 33 dead rats analyzed between 2019 and 2022 were collected from Zoo Atlanta in Georgia
Rats become infected when they eat snails and slugs that harbor worm larvae. Once rats ingest it, the parasite makes its way through their body and reaches the central nervous system. The parasite releases eggs into the rat’s pulmonary artery and they then travel through the bloodstream, only to pass into the rat’s 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 Zoo Atlanta had the parasite in their lungs, brain and heart tissue.
The parasite’s natural life cycle begins and ends with rodents becoming infected when they eat snails and slugs that harbor the worm larvae.
Humans are more likely to become infected when they eat slugs or infected vegetables covered in slug slime, but they cannot transmit it to another human.
Most people who become infected with lungworms recover without medical treatment.
But if the worm infects a human and then travels to the brain, it can cause a rare case of eosinophilic meningitis caused by inflammation of the membranes that cover the brain and spinal cord.
From 2019 to 2022, veterinarians at the University of Georgia, Texas A&M University, Mississippi State University and Zoo Atlanta in Georgia’s capital conducted tests on 33 dead brown rats found on zoo grounds.
Specifically, they examined tissue from the dead rats’ brain, heart, liver, kidneys, lungs, spleen, skeletal muscles, skin, gastrointestinal tract, adrenal glands, and gonads.
Seven of the rats had worms, or nematodes, as researchers call them, in their heart, pulmonary artery and brain tissues.
Of those seven, four were confirmed to be infected with lungworms. The remaining three were not confirmed to have lungworms, but researchers noted that they had worms in their blood vessels that were consistent with A. cantonensis.
Lungworm had previously been detected in rats in Florida and Alabama, leading researchers to believe that lungworm was likely present in Georgia long before the first dead rats were examined in 2019.
At least six cases of the parasite in humans had also been found in a six-year span across the Southeast.
The researchers saying: “The discovery of indigenous cases of A. cantonensis infection in rodent definitive hosts collected between 2019 and 2022 in the state of Georgia suggests that this zoonotic parasite was introduced and 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 a red flag for epidemiologists who have been tracking the spread of diseases from their hometowns to remote places like 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 like the southeastern United States a suitable living environment.
A prolonged warm season also means a longer time for the parasite to flourish and infect more species.
Lungworm gets its name from the characteristic way it exploits the host rat’s own respiratory system to grow.
The parasite’s life cycle begins when eggs pass through a rat’s feces and hatch in the environment into what researchers call first-stage larvae, or L1.
Snails and slugs then devour larvae from the environment when they feed. In the snail’s digestive system, the larvae enter their second stage of life. By the time it reaches the third stage of development, it has acquired the ability 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 the eggs are released and circulate through the bloodstream.
Humans who eat infected snails or slugs, often by challenge according to the CDC, are more likely to become infected, but are not guaranteed to experience any symptoms.
They may first experience nausea and vomiting within a few hours to a few days after eating a contaminated snail. There is no designated treatment for lungworm and it usually resolves on its own.
Neurological symptoms such as headache, stiff neck, tingling or tingling sensation in the extremities, and sensitivity to light may occur.
Eosinophilic meningitis as a result of lungworm infection is rare and only Around 3,000 documented cases worldwide. since 1944. However, this may be an undercount, as many cases may go undiagnosed and untreated.