Raccoon Roundworm

(Baylisascaris)

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.

Distribution

Geographic:

The distribution of B. procyonis mirrors that of raccoons.
Raccoons occur in the Lower Mainland, southern BC and Vancouver Island. 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.

Seasonality:

New infections begin in young raccoons ingesting infective eggs of B. procyonis in late spring and early summer.

Hosts and Life Cycle

Two alternate life cycles: one in Raccoons; one in other susceptible, accidental hosts.
For a visual description of Life Cycles described below, click on this link at the US Centres 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 more often seen in young raccoons than adults.

Life Cycle:

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, infective larvae develop within the eggs.

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 Hosts:

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.

Life Cycle:

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 accidental hosts may migrant 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 including imbalance, circling and abnormal behaviour.

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 colour, measure 9-22 cm in length and 1 cm in thickness.

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.

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 and 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-coloured spheres, 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 irritations from larval migrating within the skin
- eye and brain tissue damage due to the random migration of the larvae
- individuals may experience nausea, a lethargic feeling, incoordination and loss of eyesight

Meat Edible?

Raccoon meat is generally not consumed. 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 inhabitation 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 de-worm all raccoons that come under their care, although this is no guarantee that all parasites are removed.

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

Neurological symptoms are very similar to rabies and other wildlife diseases that affect the central nervous system.
Other disease agents which may elicit similar neurological symptoms include:
- pesticides
- trauma
- sarcosystosis
- bacterial and viral inflammation of the brain