A disease that can cause neurological illness and meningitis in people, rat lungworm, has been found in wild opposums, rats and a zoo animal in San Diego County, indicating its establishment in California for the first time.
Researchers reported their findings in the journal Emerging Infectious Diseases, published by the U.S. Centers for Disease Control and Prevention. The authors, who include veterinarians, researchers and wildlife biologists, urged physicians and other healthcare workers in the region to consider lungworm infection when patients come in with nervous system disorders.
The discovery highlights “a notable expansion of the range of this parasite in North America,” they said.
The CDC website says the risk to the general public of getting this infection is low, but it can be deadly.
If ingested, the worms can cause severe headaches, stiff neck, the sensation of tingling or painful skin, low-grade fever, nausea, vomiting, coma and sometimes death. People who eat freshwater crab, prawns, frogs, snails and slugs are at greatest risk. However, people can also get the disease by eating un-rinsed produce that’s been slimed by a snail or slug, or eating a slug or snail that was chopped up in produce. The worms need moisture, however; if the produce is dry, the worms will die.
Domestic animals, including dogs and cats, are also at risk.
Officials with the California Department of Public Health were not ready to call the disease endemic, or established, in the state.
“Additional surveillance and testing will be necessary to determine whether the detections of rat lungworm in the animals evaluated in San Diego County represent an isolated introduction of the parasite or ongoing local transmission,” spokeswoman Elizabeth Manzo wrote in a statement to The Times.
The department said it is not aware of rat lungworm outside San Diego County, and has seen no human cases.
“However, the San Diego study affirms that the parasite can be introduced to California through movement of infected animals from endemic areas,” the statement said. “Because some species of snails and slugs present in California are capable of serving as hosts for rat lungworm, and the presence of the parasite in other parts of the state is unknown, it is advised to take certain food safety precautions. Persons should not consume any raw or undercooked wild snails or slugs, and should thoroughly wash all produce before consuming.”
The worms that cause the disease, Angiostrongylus cantonensis, are native to Southeast Asia. They’ve been found in the U.S. since the 1960s — including in isolated human and zoo animal cases in California — and are established in Hawaii as well as in much of the southeastern U.S.
It is believed they came overseas via rats on boats.
The worms favored environment is the moist, warm bed of a rat’s lung. When a rat is infected, the worms cause respiratory distress, priming the rodent to cough. Worm-filled sputum is then ejected into the rat’s mouth, and swallowed. The rat then poops the worms out, and animals such as slugs and snails eat the poop. When a rat eats an infected invertebrate, the cycle begins again.
Occasionally, another animal, such as a raccoon or dog, or a person, will accidentally eat an infected animal, or the slime of one, and contract the disease.
The discovery of the worm in San Diego County rodents and opossums was made by staff at the San Diego Zoo and a local wildlife rehabilitation center, Project Wildlife, which is run by the San Diego Humane Society.
In December 2024, a 7-year-old male parma wallaby, born and raised at the zoo, began showing concerning neurological behaviors: incessant head shaking, blindness, a lack of muscle coordination and paralysis in his hind legs. He was euthanized after 11 days in the zoo infirmary.
When zoo staff examined the body, they found six rat lungworms in the marsupial’s brain, along with a lot of damage.
Because the diagnosis was so unusual, zoo staff examined the bodies of 64 free-ranging roof rats that had either been euthanized in the course of regular pest control or found dead on the property. Two, a little more than 3%, had lungworms. Their feces had them too: “numerous live … larvae with coiled posterior ends.” The larvae, roughly 300 in each poop sample, were each about the size of a grain of sand.
Officials at the San Diego Zoo did not respond to requests for comment.
Curiously, at the same time the zoo investigation was underway, staff from Project Wildlife had been dealing with sick opossums brought to them from around the county. Tests of 10 dead animals showed seven carried the lungworms.
Many people and animals remain asymptomatic when they’re infected. Symptoms typically appear within hours or days after ingestion and can last up to eight weeks. The worms will eventually die.
Because the disease has so many varied symptoms, health officials say it can go undiagnosed and untreated. Health officials from Hawaii, where the disease is endemic, say if lungworms are suspected, it’s best to be treated as soon as possible — even before lab results come back.
The CDC too notes that treatment works best when the disease is caught early, and can consist of high doses of corticosteroids, lumbar punctures for symptomatic relief of headaches, and antiparasitic medications, such as albendazole.
