CDC Reports Neurologic and Ocular Disease Caused by Raccoon Roundworm Infection

The raccoon roundworm Baylisascaris procyonis can cause death or serious neurologic disease in people. From 1973 through 2010, 22 documented cases of baylisascariasis were reported in humans in the United States. In an article recently published in Morbidity and Mortality Weekly Report, the Centers for Disease Control and Prevention (CDC) reported an additional seven cases of human baylisascariasis. The cases occurred in six states from May 2013 through December 2015.

“Humans become infected with Baylisascaris procyonis by ingesting embryonated (fertile) eggs,” said lead author Anita D. Sircar, MD, in an interview. “Anyone who is exposed to environments where raccoons live is potentially at risk. Young children or developmentally disabled persons are at highest risk for infection as they may be more likely to put contaminated fingers, soil, or objects into their mouths.”

The seven people included in the CDC report ranged in age from 10 months to 63 years and lived in six states: California, Ohio, Oklahoma (this patient later presented with symptoms in Arkansas), Massachusetts, Minnesota, and Virginia. Six patients developed neurologic signs and one developed ocular signs.

“Because there is no commercially available serologic test for baylisascariasis, a history of raccoon exposure and a high index of clinical suspicion are necessary to make the diagnosis,” write the authors. All seven of the patients described in the report lived, worked, or hiked in areas where raccoons were commonly found. One patient kept a pet raccoon; another was a child who played in a garage where raccoon pelts (from hunting) were stored. The others had no known direct contact with raccoons.

Serum and/or cerebrospinal fluid samples of all seven patients were positive for antibody to B procyonis by the rBpRAG1 Baylisascaris immunoblot assay. A positive antibody test indicates exposure to Baylisascaris but does not confirm active infection. The six patients with neural larval migrans all had cerebrospinal fluid eosinophilia. In the patient with ocular larval migrans, a larva was seen on retinal imaging.

All seven patients were treated with corticosteroids, and all but one received albendazole. All of the patients in this report survived, although four had serious neurologic complications. The patient with ocular larval migrans recovered almost all of the vision in the affected eye.

The CDC recommends the following steps to prevent transmission of Baylisascaris to people:

• Avoid contact with raccoons and their feces.
• Wash hands after soil contact or outdoor play.
• Teach children not to put soil in their mouths.
• Do not keep raccoons, other potential host species (such as skunks and kinkajous), or wild animals as pets.
• Have dogs regularly tested for parasites and dewormed by a veterinarian.
• Avoid and clear areas where raccoons defecate.

Dogs can become infected with B procyonis by ingesting eggs either from the environment or through paratenic hosts that carry the larvae in their tissues, according to the Companion Animal Parasite Council (CAPC). The CAPC Baylisascaris page includes an image of B procyonis and Toxocara canis ova side by side for comparison. Infection rarely causes clinical disease in dogs, although neurologic signs have been reported. Dogs should be treated because of the zoonotic potential of the disease. According to the CAPC, most drugs that treat T canis in dogs can also be used to treat B procyonis, although none are specifically approved for treatment of Baylisascaris and retreatment may be needed.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC.