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by Richard D. Pearson, MD

Baylisascariasis is infection with the raccoon ascarid, Baylisascaris procyonis, which may cause fatal CNS infection in humans.

Infection usually occurs in children who play in dirt or with articles contaminated with raccoon feces. It occurs in the US, particularly in the Middle Atlantic, Midwest, and Northeast. Although baylisascariasis is rare in people, it is of concern because a large number of raccoons live near humans and the infection rate of B. procyonis in these animals is high.

Migration of the larvae through a wide variety of tissues (liver, heart, lungs, brain, eyes) results in VLM and OLM syndromes, similar to those due to toxocariasis. However, in contrast to Toxocara larvae, Baylisascaris larvae continue to grow to a large size (up to 24 cm for females and 12 cm for males) within the CNS and cause eosinophilic meningoencephalitis. Tissue damage and symptoms and signs of baylisascariasis are often severe because Baylisascaris larvae tend to wander widely and do not readily die.

Diagnosis is difficult because serologic tests are not commercially available, but CSF or serum can be tested for antibodies at the Centers for Disease Control and Prevention if the index of suspicion is high. Viewing a larva during ocular examination is often a clue.

When suspicion of infection is high, immediate treatment with albendazole (25 to 50 mg/kg po once/day for 10 to 20 days) may be effective.

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