Parasite Profile: Raccoon Roundworm


Baylisascaris procyonis is a raccoon roundworm that can infect other animals and, rarely, humans.  A high percentage of raccoons are infected with baylisascaris. These roundworms grow in the raccoons’ intestines and produce millions of eggs that are shed into the environment in the raccoons’ feces. After 2-4 weeks in the environment, eggs become infectious; under the right conditions, eggs can survive in the soil for years. (1)

Humans become infected by ingesting embryonated (fertile) eggs. Anyone who is exposed to environments where raccoons frequent 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. (2)


Baylisascaris infection may cause:

  • Nausea
  • Fatigue
  • Loss of coordination and muscle control
  • Inability to focus attention
  • Enlargement of the liver
  • Blindness
  • Coma

Symptoms start approximately a week after exposure. (1)


Prevention & Control

Baylisascaris infection can be prevented by avoiding contact with raccoons and their feces. Washing your hands after working or playing outdoors is good practice for preventing a number of diseases.

Do not keep, feed, or adopt wild animals, including raccoons, as pets. Infection rarely causes symptoms in raccoons, so you cannot tell if a raccoon is infected by observing its behavior. Roundworm eggs passed in the feces of infected raccoons are not visible to the naked eye. Eggs can only be seen using a microscope.

Raccoons may use sandboxes as a latrine. Keep sandboxes covered when not in use.

You may discourage raccoons from living in and around your home or parks by taking these steps:

  • prevent access to food
  • keep trash containers tightly closed
  • close off access to attics and basements
  • keep sandboxes covered when not in use (raccoons may use sandboxes as a latrine)
  • remove fish ponds — they eat the fish and drink the water
  • eliminate water sources
  • remove bird feeders
  • clear brush so raccoons are not likely to make a den on your property (2)

Documented Cases of Baylisascarisiasis Infections in Humans in Canada:

“Raccoon roundworm (Baylisascaris procyonis) is a cause of devastating neural and ocular disease. The first documented case of raccoon roundworm encephalitis in Canada, is a seven-year-old boy who presented with severe neurological impairment…”

“In 2008, a 14-month-old previously healthy boy in Hamilton, Ontario, Canada, sought care for fever, regression in speech for 5 days, and failure to bear weight for 2 days. His parents also noticed that he was not tracking with his eyes. Caregivers recalled a macular rash on the face and trunk that had faded over time. The child was hospitalized, and a workup for encephalitis was initiated. He was hemodynamically stable and had flaccid tone, with inability to bear weight. No visible rashes were found.”

“We report the case of a 73-year-old female nursing home resident with a 10-year history of moderately severe Alzheimer-type dementia… Autopsy findings showed a large pulmonary embolus as the cause of death. Mild, diffuse cerebral atrophy was the only gross brain abnormality (brain weight 1,210 g). Examination by microscopy was restricted to the brain and demonstrated Alzheimer-type pathology that was sufficiently severe to account for the patient’s dementia. In addition, sections of deep white matter from the left frontal lobe showed a small number of lesions, each consisting of a single larval nematode surrounded by mild chronic reactive changes and inflammation (macrophages, lymphocytes, plasma cells, and rare eosinophils) (Figure, panel A). Inflammation and reactive changes were restricted to the tissue immediately surrounding the larvae.”


(1) BC Center for Disease Control

(2) Centers for Disease Control and Prevention

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