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.
(See also Approach to Parasitic Infections.)
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 of Baylisascariasis
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 of Baylisascariasis
Prevention of Baylisascariasis
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 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.
Collections of raccoon feces (raccoon latrines) are biohazards and are best removed by professionals.
