What to Know About ‘Raccoon Roundworm’

While two people in Los Angeles County recently were infected with “raccoon roundworm,” the infection is rare and doesn’t pose a widespread threat, experts said.

The parasite that causes the disease, Baylisascaris procyonis, lives in the intestines of raccoons. While it doesn’t make them sick, eggs can be excreted in the animals’ feces and people can become infected when they accidentally ingest those eggs, according to the Los Angeles County Department of Public Health.

Once ingested, the eggs hatch into larvae, penetrate the gut wall, and migrate through tissues, according to a 2023 case report on raccoon roundworm infection published by Beth Lipton, DVM, MPH, of the Washington State Department of Health, and colleagues in the CDC’s journal Emerging Infectious Diseases. Larvae can infect other organs, the eyes, and the brain, causing larva migrans syndrome, the report stated.

Infection often manifests as acute eosinophilic meningitis, Lipton and colleagues wrote. Migrating larvae are mostly found in muscle tissue, and less than 5% of migrating larvae reach the brain.

According to the CDC, the parasite’s incubation period is usually 1 to 4 weeks. Symptoms can include nausea, fatigue, enlarged liver, loss of coordination, loss of muscle control, and impaired vision, among others.

A review of the literature turned up 37 cases of Baylisascaris procyonis infection in North America, with 33 cases in the U.S. and four in Canada. Patients had a median age of 1.6 years, 82% were male, and 18% of cases resulted in death, according to the CDC report.

Geophagia (eating earth or soil-like substances) or pica (a disease where people eat things not usually considered food) was mentioned in 55% of cases, and 33% had developmental disabilities, leading researchers to conclude that young children and people with developmental delays are at high risk for raccoon roundworm infection because of “hand-mouth behaviors.”

Indeed, the case at the center of the CDC report had autism spectrum disorder and a history of pica. In addition, experts found a raccoon latrine — the communal locations where raccoons are often known to defecate — in the patient’s backyard.

Baylisascaris procyonis infection can be treated with the broad-spectrum anthelmintic albendazole (Albenza) along with corticosteroids during the early stage of the infection, which may reduce serious tissue damage. However, Lipton and colleagues cautioned that “no treatments are totally effective.”

While Los Angeles County public health officials noted that the risk to the public remains low, they warned people to take caution as raccoons live in close quarters with humans — and the Baylisascaris procyonis infection rate among raccoons is likely very high, at an estimated prevalence of 68% to 82%, according to the CDC report.

Officials noted that the infection can’t transmit human-to-human, and while it can infect household pets such as cats and dogs, it’s not likely to be passed on by them.

The cases have no connection to the ringworm cases in New York that were reported earlier this summer. Ringworm isn’t a parasitic infection, but a fungal infection.

In June, researchers reported the first case of a sexually transmitted ringworm infection in the U.S. known as Trichophyton mentagrophytes type VII, which occurred in a man in his 30s from New York City who developed ringworm on his genitals, buttocks, and limbs after reporting having sex with men during trips to California, England, and Greece.

A month prior, the same research group reported 11 cases of severe drug-resistant Trichophyton indotineae ringworm infections linked to travel to Asia.

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