OVERVIEW: What every practitioner needs to know

Baylisascariasis in humans is caused by infection with the raccoon roundworm, Baylisascaris procyonis. This parasite causes severe or fatal encephalitis (neural larval migrans), most often in infants and young children. It usually manifests as an eosinophilic meningoencephalitis.

Humans become infected by ingesting soil, woodchips, or other material contaminated with raccoon feces containing B. procyonis eggs. Pica and geophagia are risk factors. Not only raccoons but also kinkajous, coatis, and other procyonids can harbor this roundworm.

Most of the limited number of reported human cases have occurred in boys, who present with an acute fulminant eosinophilic meningoencephalitis, with fever, ataxia, progressive lethargy, irritability, and somnolence. Ultimately, loss of milestones and regression develop, leading to posturing, spasticity, paresis, seizures, and ocular or cranial nerve involvement. Mortality is high, and survivors almost always are severely disabled.

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Treatment is mostly supportive.

Key symptoms and signs

There is evidence of acute eosinophilic meningoencephalitis, with a progressive decline in level of alertness, loss of milestones, spasticity. and posturing. Cerebrospinal fluid (CSF) demonstrates eosinophilic meningitis, with mildly increased numbers of white blood cells, greater than 10% eosinophils, normal glucose levels, and normal to mildly elevated protein levels.

What other disease/condition share some of these symptoms?

Eosinophilic meningitis is quite uncommon. Other helminthic causes are Angiostrongylus cantonensis (endemic in Asia, Pacific region) and
Gnathostoma spinigerum. Toxocara, the cause of visceral larval migrans, rarely causes neural larval migrans. Disseminated Coccidiodes immitis can lead to eosinophilic meningitis.

Tuberculous meningitis and viral meningoencephalitis are not associated with eosinophilia but should be included in the initial differential diagnosis based on signs and symptoms.

What laboratory tests should you request to help confirm the diagnosis? How should you interpret the results?

Peripheral eosinophilia (median = 28%) and CSF eosinophilia (median = 32%) are common. CSF pleocytosis is mild. CSF usually shows normal glucose levels and normal to slightly increased protein levels. Increased isohemagglutinins (anti-A, anti-B blood group antigens) may be present in serum. Anti–B. procyonis antibodies can be detected in CSF and serum (test available only from the Department of Veterinary Pathology, Purdue University, West Lafayette, IN).

Brain biopsy can demonstrate B. procyonis larvae in tissues. Electroencephalography usually shows diffuse nonspecific slow waves but can be normal.

B. procyonis eggs or larva are notfound in stool of infected patients because the parasitic life cycle is not completed in humans.

Would imaging studies would be helpful? If so, which ones?

In acute B. procyonis neural larval migrans, magnetic resonance imaging and computed tomographic findings lag behind clinical disease. Imaging may be normal initially but eventually shows diffuse nonspecific white matter abnormalities, especially in cerebral periventricular and deep cerebellar regions. Hydrocephalus, cerebral edema, and loss of gray-white differentiation may develop.

Confirming the diagnosis

  • A young child (especially a boy) presents with signs and symptoms suggesting meningoencephalitis.

  • CSF shows eosinophilia (>10% of white blood cells) and normal glucose levels.

  • Consider B. procyonis infestation (neural larval migrans).

What are the adverse effects associated with each treatment option?

Prognosis is very poor with or without treatment. The usual therapy includes antihelminthic agents plus steroids. Thiabendazole, fenbendazole, tetramisole, and ivermectin have been used, but albendazole is favored because of its excellent CSF penetration and larvicidal activity.

What are the possible outcomes of Baylisascaris procyonis?

Up to one half of affected patients may die. All reported survivors except one were left with very significant neurologic sequelae.

How does this pathogen cause disease?

Ingestion of B. procyonis eggs by young humans with pica or geophagia leads to hatching of the eggs in the gut. The larvae penetrate the gut wall and migrate to the brain (as well as to eye or viscera). Migration of larvae through the brain (neural larval migrans) causes tissue damage, leading to granulomas, eosinophilic inflammation, and necrosis.

Other Clinical Manifestations

Ocular larval migrans also can result from B. procyonis, either in isolation or with severe neural larval migrans. This can lead to visual impairment or blindness. Chorioretinitis, optic neuritis, or atrophy can result.

Visceral larval migrans can occur from B. procyonis larvae and affects heart, lungs, mediastinum, bowel, and mesenteric lymph nodes.

How can Baylisascaris procyonis be prevented?

Prevention of this devastating infection involves (1) educating the public regarding the dangers of contact with raccoons and their feces, (2) discouraging pica in young children, (3) handwashing after outdoor play or animal contact, (4) discouraging raccoon visitors or pets, (5) decontaminating raccoon latrines, and (6) avoiding feeding raccoons.

What is the evidence?

Gavin, PJ, Shulman, ST. “Raccoon roundworm (Balisascaris procyonis)”. Pediatr Infect Dis J. vol. 22. 2003. pp. 651-652. (This is a brief but helpful review of this organism and the disease it can cause.)

Gavin, PJ, Kazacos, KR, Tan, TQ, Brinkman, WB, Byrd, SE, Davis, AT, Mets, MB, Shulman, ST. “Neuroal larva migrans caused by the raccoon roundworm “. Pediatr Infect Dis J. vol. 21. 2002. pp. 971-975. (The authors describe 2 children with devastating disease caused by this orgnanism.)