Baylisascaris procyonis

  Raccoon Roundworm

Rev. 08/03/2020


Phylum: Nematoda
Class:    Chromadorea
Order:   Rhabditida
Family:  Ascarididae


Morphology and Anatomy:

Baylisascaris procyonis collected from the intestine of a single raccoon.


Infected raccoons have been found throughout the United States.

The highest infection rates occur in the midwest, northeast, and west coast.


Economic Importance:

Young children may be more likely than adults to ingest the eggs due to their behavior of putting dirt and other objects into their mouths.

The very small number of reported Raccoon Roundworm infection in humans, despite the large number of raccoons living in close association with humans, suggests that the risk of infection is rare and remote.



Lives in the digestive tract of raccoons.


Intestinal roundworm

Life Cycle:

The microscopic eggs of the parasite are shed in raccoon feces  and a single defecation may carry a large number of eggs. Infected raccoons commonly shed millions of eggs in their feces, and the eggs usually develop to the infective stage in 2 - 4 weeks.

The eggs are resistant to most environmental conditions and with adequate moisture, can survive for years.

Infection occurs when infective eggs are accidentally ingested by a person or animal.  The eggs must be ingested by a human or other animal to be able to hatch and release larvae. Animals may also become infected by eating a smaller animal that has been infected with Baylisascaris.


Humans and other animals can act as paratenic hosts in which the parasite does not reach sexual maturity. When infective eggs of the roundworm are ingested by humans and other animals, Baylisascaris larvae hatch in the intestine and travel through the organs and muscles; this is called visceral larval migrans.

Signs and symptoms of infection depend on how many eggs are ingested and where in the body the larvae migrate. Once swallowed and inside the body, eggs hatch into larvae, which then migrate through the liver, brain, spinal cord, and other organs. Swallowing a few eggs may cause few or no symptoms. Ingesting large numbers of eggs may
lead to serious symptoms.

Symptoms in paratenic hosts may include nausea, tiredness, liver enlargement, lack of coordination, lack of attention to people and surroundings, loss of muscle control, coma, and blindness. Some cases have resulted in death. Signs and symptoms of infection may take a week or so after ingestion of eggs to develop. 

Serious infection of humans is rarely diagnosed; fewer than 30 cases have been reported. However, it is believed that some cases are incorrectly diagnosed as other infections or go undiagnosed.

Infection rarely causes symptoms in raccoons.


To avoid infection of humans:

No effective, curative treatment is yet available. However, because early treatment might reduce serious damage caused by the infection, seek immediate medical attention for any person seen ingesting raccoon feces.



Santa Barbara County Public Health Department

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