Raccoon Roundworm Infection in Two Los Angeles Children, 2024

Baylisascaris procyonis, the raccoon roundworm, is an intestinal parasite that commonly infects raccoons, usually without making them sick; in the Northeast, Midwest and West Coast, up to 80% of raccoons carry it. An infected raccoon can shed millions of eggs a day in its feces. The eggs become infective after 2 to 4 weeks in the environment and can survive for years. When another animal or a person swallows them, the larvae hatch and migrate through the body, into organs (visceral larva migrans), the brain (neural larva migrans) or the eye (ocular larva migrans). Without prompt treatment the infection can cause serious complications and death.

Human cases are rare: only 35 had been reported in the United States. Most were in young boys with developmental disabilities and pica, a compulsion to eat nonfood items such as soil. There is no vaccine. When exposure is strongly suspected, such as known swallowing of raccoon feces, oral albendazole (25–50 mg/kg a day for 10–20 days) may be given, ideally within three days.

Two children

On September 4, 2024, a physician at Children's Hospital Los Angeles told the Los Angeles County Department of Public Health about two possible cases. Both families agreed to have the cases described.

Patient A, a 14-year-old boy with autism spectrum disorder and a history of pica, was hospitalized in May 2024 after a week of sleepiness, reduced activity, confusion and unsteady walking. His blood showed mild eosinophilia (14% eosinophils, more than 1,000 per mL). As he worsened, a brain MRI showed many lesions, and his cerebrospinal fluid was 15% eosinophils. A clinician who had seen a case before suspected raccoon roundworm. An eye examination found a live nematode in his eye, which was destroyed with a laser. With CDC's advice he was immediately given six weeks of albendazole and corticosteroids. CDC testing found his blood weakly positive for antibodies to the parasite and his spinal fluid negative, a pattern seen before. He recovered and returned to his usual neurologic state.

Patient B, a previously healthy 15-month-old boy who had been meeting his developmental milestones, was hospitalized in June 2024 with brain dysfunction, lethargy, weakness, unsteady walking and increasing muscle stiffness. His blood was 53% eosinophils, his spinal fluid showed eosinophils (16%), and an MRI showed widespread changes in the brain's white matter. At two children's hospitals he was treated for suspected acute disseminated encephalomyelitis, with intravenous immunoglobulin, corticosteroids, rituximab and plasma exchange, and after six weeks he went home with a feeding tube. Three months after his symptoms began, he saw the same clinician who had treated patient A, who noted the same striking eosinophil counts and suspected raccoon roundworm. A live nematode was again found in his eye and destroyed by laser, and he was given six weeks of albendazole and corticosteroids. His test results matched patient A's. He has persistent, severe cognitive, motor and vision impairments.

Looking for the source

At patient A's home, the family often saw many raccoons, and neighbors regularly left food out for community cats, which can attract raccoons. The family also had a dog. Investigators found a raccoon latrine, a shared defecation site, on the sloping roof directly above the entrance, where feces rolled down onto the landing, and dried feces on the back stairs. Given his pica, he may have eaten feces or contaminated soil there. The health department recommended removing the latrine, decontaminating the area and keeping raccoons out, but those efforts failed and raccoons kept coming. Because the risk continued, two of his siblings, one of whom also had pica, were given a 10-day preventive course of albendazole, and the family planned to move.

At patient B's home and child care center, investigators found no sign of raccoons or latrines, though raccoons lived in the neighborhood, and no other children at the center were ill. His family said he had repeatedly put soil and bark mulch in his mouth at home, in parks and at the beach. No source was identified.

The public health response

• Health workers visited 476 households within eight blocks of patient A's home and 35 child care centers in the wider area, handing out information on the disease and how to prevent it.
• The county issued a press release and webpage, a health alert for clinicians on recognizing, diagnosing, treating and reporting the infection, and an advisory for veterinarians, since dogs can also carry the adult worms and shed eggs.

Lessons

The true number of human infections is unknown. A study in Santa Barbara County found antibodies in 7% of the general population, suggesting mild or symptomless infections are more common than thought. Delay can be devastating, as patient B's roughly three-month wait for a diagnosis showed, and both cases were recognized only because one clinician had seen the disease before, which suggests others may be missed.

For clinicians: consider raccoon roundworm in any patient, especially a young child or a person with developmental disabilities or pica, with worsening neurologic symptoms and high eosinophils in blood or spinal fluid, even without known raccoon contact, and consider treating with albendazole right away.

For everyone:

• Avoid contact with raccoons and their feces, and never keep raccoons as pets.
• Keep young children and people with developmental disabilities from putting contaminated objects or fingers in their mouths, and wash hands after being outdoors.
• Safely remove raccoon latrines, checking flat places raccoons favor, such as rooftops, decks, tree stumps and unsealed attics.
• Discourage raccoons: remove food and water sources, keep trash tightly closed, block access to basements, attics and crawl spaces, clear brush and branches away from the house and roofline, and cover sandboxes when not in use.
• Keep dogs from eating raccoon feces, give pets year-round parasite prevention that includes a dewormer effective against this roundworm, and have a veterinarian check their feces at least once a year.

Sources

• Vaughan AM, Kamel D, Chang M, et al. Baylisascariasis (Raccoon Roundworm Infection) in Two Unrelated Children — Los Angeles County, California, 2024. MMWR Morb Mortal Wkly Rep 74(28). https://www.cdc.gov/mmwr/volumes/74/wr/mm7428a1.htm
• CDC, preventing raccoon roundworm: https://www.cdc.gov/baylisascaris/prevention/index.html
• The report was led by the Los Angeles County Department of Public Health with Children's Hospital Los Angeles and CDC; its figures are not reproduced here.