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Baylisascariasis

By Richard D. Pearson, MD, Emeritus Professor of Medicine, University of Virginia School of Medicine

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Patient Education

Baylisascariasis is a rare 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. Most cases have been reported in the Middle Atlantic, Midwest, and Northeast of the US. 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.

Infected raccoons shed millions of eggs daily in their feces; the eggs can survive in the environment for years. Humans become infected by ingesting infective eggs.

After ingestion by humans, the eggs hatch into larvae. The larvae migrate through a wide variety of tissues (liver, heart, lungs, brain, eyes), resulting in visceral larva migrans and ocular larva migrans, 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. Larvae in the CNS can cause inflammatory reactions and eosinophilic meningoencephalitis, damage tissue, and become encapsulated in granulomas.

The severity of neurologic disease in humans varies depending on the

  • Number of eggs ingested

  • Number of larvae migrating in the CNS

Tissue damage and symptoms and signs of baylisascariasis are often severe because Baylisascaris larvae tend to wander widely and do not readily die.

Diagnosis

  • MRI

  • Antibody tests

Baylisascaris encephalitis should be considered in patients with sudden onset of eosinophilic encephalitis and a history of possible exposure to raccoons and/or to areas where racoons defecate (eg, possibly resulting in ingestion of raccoon feces or contaminated soil).

Characteristic findings include CSF eosinophilic pleocytosis, peripheral eosinophilia, and deep, especially periventricular, white matter abnormalities seen on an MRI scan.

Diagnosis of baylisascariasis is difficult because serologic tests are not commercially available, but CSF or serum can be tested for antibodies at the CDC if the index of suspicion is high.

Viewing a larva during ocular examination is also a clue.

Treatment

  • Albendazole

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.

Key Points

  • Baylisascariasis, a raccoon infection, is rare in people, but it is a concern because a large number of raccoons live near humans and the infection rate of B. procyonis in raccoons is high.

  • Baylisascariasis usually occurs in children who play in dirt or with articles contaminated with raccoon feces.

  • Tissue damage and manifestations 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 CDC.

  • When suspicion of baylisascariasis is high, immediate treatment with albendazole may be effective.

Drugs Mentioned In This Article

  • Drug Name
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  • ALBENZA

* This is the Professional Version. *