Merck Manual

Please confirm that you are a health care professional

Loading

Baylisascariasis

By

Richard D. Pearson

, MD, University of Virginia School of Medicine

Last full review/revision Sep 2020| Content last modified Sep 2020
Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version

Baylisascariasis is a rare infection with the raccoon ascarid, Baylisascaris procyonis, which may cause fatal central nervous system (CNS) infection, ocular disease, or a visceral larva migrans syndrome 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 United States. 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. Nonspecific symptoms such a fever, lethargy, and nausea may develop as early as a week after ingestion. 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 central nervous system (CNS). Neurologic abnormalities typically appear 2 to 4 weeks after ingestion of large numbers of infective eggs. Larvae in the CNS cause inflammatory reactions, eosinophilic meningoencephalitis, and substantial tissue damage resulting in altered mental status, irritability, cerebellar abnormalities, ataxia, stupor, and coma. Death or permanent disability often result, even with treatment.

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 cerebrospinal fluid (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 Centers for Disease Control and Prevention (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 orally once a day for 10 to 20 days may be effective. Presumptive treatment should be started as soon as possible after ingestion of potentially infectious material, ideally within three days. If albendazole is not available, mebendazole or ivermectin can be used until it is obtained.

Prevention

To prevent baylisascariasis, it is important to discourage raccoons from living in or close to houses. Sandboxes should be covered when not in use. Raccoons use the same communal spot to defecate, leaving a large amount of tubular, foul smelling feces in one area (called a raccoon latrine). Raccoon latrines are biohazards because of the high likelihood of parasitic contamination, and their removal is best left to professionals. (See also the Centers for Disease Control and Prevention (CDC) Raccoon Latrines: Identification and Clean-up.)

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 are large, tend to wander widely and do not readily die in humans.

  • Diagnosis is difficult because serologic tests are not commercially available, but cerebrospinal fluid (CSF) or serum can be tested for antibodies at the Centers for Disease Control and Prevention.

  • When suspicion of baylisascariasis is high, immediate treatment with albendazole may be effective. Presumptive treatment is started as soon as possible if a person ingests soil or sand likely to be contaminated with raccoon feces.

  • Collections of raccoon feces (raccoon latrines) are biohazards and are best removed by professionals.

Click here for Patient Education
NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version

Also of Interest

Videos

View All
Overview of Lyme Disease
Video
Overview of Lyme Disease
3D Models
View All
SARS-CoV-2
3D Model
SARS-CoV-2

SOCIAL MEDIA

TOP