Baylisascaris infection

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

A baylisascaris infection is an infection caused by an intestinal raccoon roundworm that can infect a variety of other animals, including humans. The worms develop to maturity in the raccoon intestine, where they produce millions of eggs that are passed in the feces. Released eggs take 2-4 weeks to become infective to other animals and humans. The eggs are resistant to most environmental conditions and with adequate moisture, can survive for years. The infection is rarely diagnosed, and can cause severe damage and lead to death in humans if left undiagnosed and untreated.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Baylisascaris procyonis completes its life cycle in raccoons, with humans acquiring the infection as accidental hosts (dogs serve as alternate definitive hosts, as they can harbor patent infection and shed eggs).

1. Unembryonated eggs are shed in the environment, where they take 2-4 weeks to embryonate and become infective.
2. Raccoons can be infected by ingesting embryonated eggs from the environment. Additionally, over 100 species of birds and mammals (especially rodents) can act as paratenic hosts for this parasite:
3. Eggs ingested by these hosts hatch and larvae penetrate the gut wall and migrate into various tissues where they encyst.
4. The life cycle is completed when raccoons eat these hosts.
5. The larvae develop into egg-laying adult worms in the small intestine and eggs are eliminated in raccoon feces.
6. Humans become accidentally infected when they ingest infective eggs from the environment; typically this occurs in young children playing in the dirt.
7. Migration of the larvae through a wide variety of tissues (liver, heart, lungs, brain, eyes) results in VLM and OLM syndromes, similar to toxocariasis.
8. In contrast to Toxocara larvae, Baylisascaris larvae continue to grow during their time in the human host.
9. Tissue damage and the signs and symptoms of baylisascariasis are often severe because of the size of Baylisascaris larvae, their tendency to wander widely, and the fact that they do not readily die. Diagnosis is usually made by serology, or by identifying larvae in biopsy or autopsy specimens.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Baylisascaris infections are rarely diagnosed. Fewer than 25 cases have been diagnosed and reported in the United States as of 2003. However, it is believed that cases are mistakenly diagnosed as other infections or go undiagnosed.

Human cases have been reported in Oregon, California, Minnesota, Illinois, Michigan, New York, and Pennsylvania. Of the reported 25 cases in the US since 2003, five of the infected persons died.

Raccoons infected with Baylisascaris procyonis appear to be common in the Middle Atlantic, Midwest, and Northeast regions of the United States and are well documented in California and Georgia. Proven human cases have been reported in California, Oregon, New York, Pennsylvania, Illinois, Michigan, and Minnesota, with a suspected case in Missouri.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Anyone who is exposed to environments where raccoons frequent is potentially at risk. Young children or developmentally disabled persons are at highest risk for infection as they may be more likely to put contaminated fingers, soil, or objects into their mouths.

Hunters, trappers, taxidermists, and wildlife handlers may also be at increased risk if they have contact with raccoons or raccoon habitats.

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