Baylisascaris (Raccoon Roundworm) Do Not Eat Do Not Feed To Pets Transmissable To Humans Wash Thoroughly
Causative Agent
  • Parasitic and zoonotic disease of mammals and birds caused by infection with the roundworm (Nematode), Baylisascaris procyonis.
  • Immature (larval stages) of the worm migrate through tissues and may cause extensive damage in susceptible hosts. This is a trait shared by other roundworms.
Click on image to enlarge.
Raccoon roundworms are found in the small intestines of infected animals.
  • The distribution of B. procyonis mirrors that of raccoons (Procyon lotor).
  • Raccoons are regularly found in the Lower Mainland, southern BC and Vancouver Island, although their range is expanding.
  • A recent study in southwestern BC indicated that the number of raccoons infected with B. procyonis was 61%.
  • As raccoons are increasingly being brought as pets to new locations, the geographic range of B. procyonis will continue to expand.
  • New infections begin in young raccoons that have ingested infective eggs of B. procyonis in late spring and early summer.
Hosts and Life Cycle
  • Two alternate life cycles occur: one in raccoons, and the other in susceptible, incidental (abnormal) hosts.
  • For a visual description of life cycles described below, please visit the US Centre for Disease Control and Prevention.
  • Definitive Host:
    • Adult worms are found in the small intestine of the raccoon.
    • Disease resulting from migrating larvae is rarely observed in raccoons. Although, when disease is detected, it is seen in young raccoons more often than adults.
    • Adult worms produce eggs that are shed in the feces. This can amount to millions of eggs released per day/raccoon.
    • Within a month in the external environment, larvae develop within the eggs, which are then infective.
    • Eggs may persist in the environment for years and are resistant to common disinfectants. Burning is said to be the most effective method of destroying the eggs.
    • Infective eggs are ingested by susceptible young raccoons OR infection may occur after eating another animal that has larvae in its tissues. Larvae migrate via the bloodstream through the liver to the lungs.
    • The larvae are then coughed up, swallowed, and mature into adults in the small intestine.
  • Abnormal Host:
    • Many mammals and birds have been reported as abnormal hosts, including humans, woodchucks, red and grey squirrels, porcupines, cottontail rabbits, and a number of species of ground-foraging birds.
    • Ingestion of larvae or eggs results in infection.
    • Raccoons use communal sites for defecation; other animals that forage in these areas, as well as humans coming into contact with such sites, are potentially at risk for Baylisascaris infection.
    • Larvae hatched in the gut of abnormal hosts may migrate erratically through tissues, such as lung, liver, heart and, most notably, in the eyes and central nervous system.
    • Larvae encyst in muscle, liver or the lungs.
    • Larval migration through the brain of susceptible hosts causes extensive tissue damage, resulting in severe neurological signs that include imbalance, circling and abnormal behavior.
    • Central nervous system damage has been reported in humans and a large number of wild and domestic mammals and birds.
Signs and Symptoms
  • Like other roundworms, B. procyonis are cylindrical and taper at both ends. Adult worms are tan-white in color, measure 9-22 cm in length and 1 cm in thickness.
  • In raccoons:
    • Larval migration may cause localized areas of inflammation and tissue damage or cause damage due to blockage of the small intestine by adult worms. B. procyonis infection otherwise seems to have no detrimental effects on raccoons.
  • In abnormal hosts:
    • There are usually no symptoms if the larval parasite does not enter the brain.
    • Effects are usually correlated with the number eggs ingested, the number of larvae entering the brain, extent of migration within the brain, and size of the brain relative to the size of the larval parasite.
    • Larvae may become encapsulated in tissues; these cysts are usually visible as light-colored spheres, which are 1-2 mm in diameter.
      • Clinical signs in small mammals include:
        • depression;
        • lethargy;
        • nervousness;
        • rough coat;
        • tremors in the front paws;
        • head or body tilts: slight at first, progressing to worse;
        • falling over;
        • circling;
        • posterior paralysis;
        • blindness;
        • laying on its side.
      • Clinical signs in birds include:
        • poor grip reflexes;
        • incoordination;
        • inability to fly or loss of flight control;
        • falling;
        • wing and leg paralysis.
      • Clinical signs in humans include:
        • skin irritation from larval migration within the skin;
        • eye and brain tissue damage due to the random migration of larvae;
        • individuals may experience nausea, a lethargic feeling, incoordination and loss of eyesight.
Meat Edible?
  • Raccoon meat is generally not consumed by humans. If a raccoon is to be skinned, proper protective gear should be worn (gloves, coveralls) and good hygiene should be practiced.
Human Health Concerns and Risk Reduction
  • Baylisascaris infection in humans may cause severe damage in the eyes and brain, and in extreme cases, death.
  • Minimizing the potential exposure of people to raccoon feces is the best risk reduction measure.
  • Exclusion of raccoons from areas of human habitation is warranted, as is careful attention to hygiene, particularly of children, in high-risk areas.
  • Wildlife rehabilitators, animal shelter workers and others who may come in contact with raccoon feces on a regular basis need to take particular care in the handling and disposal of raccoon feces. Additionally, these organizations should deworm all raccoons that come under their care, although this is not guaranteed to remove all parasites.
Samples for Diagnosis
  • Infection with Baylisascaris may be confirmed by finding eggs in the fecal material of live raccoons.
  • Roundworms found in the intestines of raccoons should be submitted to determine if they are B. procyonis.
  • Tissues of hosts other than raccoons that contain small cysts should be submitted to determine if B. procyonis larvae are present.
Similar Diseases
Further Reading
  • BC Centre for Disease Control Raccoon Roundworm
  • Canadian Medical Association Journal Raccoon Roundworm
  • Canadian Cooperative Health Centre Raccoon Roundworm (PDF file)
  • Michigan Department of Natural Resources Raccoon Roundworm
  • Canadian Cooperative Wildlife Heath Centre. 1995. Baylisascaris procyonis Larval migrans. Pp. 45-47. Health Risks to Wildlife personnel: Hazards from Disease-causing Agents. Canadian Cooperative Wildlife Heath Centre, Western College of Veterinary Medicine, University of Saskatchewan. Saskatoon, SK.
  • Ching H.L., Leighton B.J., Stephen C. 2000. Intestinal parasites of raccoons (Procyon lotor) from southwest British Columbia. Canadian Journal of Veterinary Research 64: 107-111.
  • Coates J.W., Siegert J., Bowes V.A., Steer D.G. 1995. Encephalitic nematodiasis in a Douglas squirrel and a rock dove ascribed to Baylisascaris procyonis. Canadian Veterinary Journal 36: 566-569.
  • Kazacos K.R. 2001. Baylisascaris procyonis and related species. Pp. 301-341 in W.M. Samuel, M.J. Pybus, A.A. Kocan (eds.), Parasitic Diseases of Wild Mammals. 3rd Ed. Iowa State University Press. Ames, IA.
Return to Manual Home Page Disease List - Body Region Affected Disease List - Causative Agent or Risk Factor Disease Surveillance Form Glossary Contact Information
Return to Manual Home Page Return to Disease List - Body Region Affected Return to Disease List - Causative Agent or Risk Factor Disease Surveillance Form Download Glossary Contact Information