Baylisascaris procyonis (Raccoon Roundworm)
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Now here is a roundworm you do not hear that much about, and hopefully you will never meet. But if you do, it is serious. Baylisascaris procyonis is a roundworm of raccoons. It does not cause severe disease in raccoons except in the young who may develop intestinal obstructions. The real hazard is when it infects humans or dogs. In man, it causes a condition called 'neural larva migrans,' or 'cerebrospinal nematodiasis.' This is a rare disease, but is serious and often fatal.

Besides dogs and humans, there are 17 other species of mammals and 19 species of birds that can serve as intermediate hosts of B. procyonis. In raccoons, B. procyonis lives in the small intestine. In man, dogs, and intermediate hosts, B. procyonis invades body organs, the central nervous system (CNS), and the eyes.

How common is B. procyonis?

One researcher suggests that B. procyonis infections account for 5% of rodent deaths in woodlots where infected raccoons are common.

B. procyonis is found throughout North America. In the Midwest, over half of the raccoons studied were infested. The prevalence of B. procyonis decreases from northern to southern states.

What is the life cycle in raccoons?

Adult worms live in the small intestine of raccoons and lay eggs that are shed in the feces. After 3-4 weeks in the environment, the eggs become infective. Young raccoons can become infected by eating these eggs. The eggs hatch, develop into larvae and mature into adults in the small intestine.

Older raccoons usually become infected by eating an intermediate host such as a mouse, squirrel, or bird that is infected with the larvae. These intermediate hosts became infected by ingesting the infective eggs from the environment or perhaps through grooming if their fur had become contaminated with the sticky eggs. In the intermediate host, larvae hatch from the eggs in the intestine and migrate to various tissues. About 5-7% of the larvae migrate to the brain of the intermediate host. There the larvae cause extensive damage. These diseased animals are easy prey, and when killed and eaten by the raccoon, the larvae from the intermediate host are released in the raccoon's intestine. These larvae develop into adults and then lay eggs.

How does B. procyonis cause disease in humans and dogs?

When people or dogs accidentally ingest B. procyonis eggs, the larvae hatch and then migrate. Injury to humans and dogs is a result of the extensive damage caused by the migrating larvae. As the larvae migrate through the host's tissues, they grow much larger in size, though they are still microscopic. Their relatively large size results in considerable mechanical damage as they migrate and the host's body produces a very strong inflammatory response. These inflammatory reactions are a major cause of damage in the CNS.

Several other species of Baylisascaris that infest badgers, skunks, fishers, martens, and bears can cause disease in man.

When large numbers of larvae are ingested, the possibility of CNS disease increases. Severe signs of disease can develop within 2-4 weeks of ingestion. Signs of disease include loss of coordination, lethargy and stupor that progresses to coma and death.

Disease can also occur if the larvae migrate to the eye. Signs include photophobia (light sensitivity) and vision loss. Larvae migrating through other body organs can produce symptoms such as fever, enlarged liver, and respiratory problems.

Since raccoons may be found in both rural and urban settings, the potential for human infection is high. Human infections have been associated with woodpiles and contaminated chimneys. Keeping raccoons as pets poses a direct threat. Wildlife rehabilitators working with raccoons and young children with poor hygiene are also more likely to be exposed.

How is infection with B. procyonis diagnosed?

In the raccoon, the eggs, which are similar in size and shape to the roundworms of dogs and cats, are found in the feces.

In man and domestic animals, the larvae may be seen in the retina of the eye during an ophthalmologic exam. Otherwise, the diagnosis is made through history, clinical signs, and serologic testing.

What is the treatment for B. procyonis infection?

This is the really scary part. There is currently no treatment for B. procyonis infection in man or domestic animals. Even if a treatment is later identified, its benefit will be of questionable value since much of the damage already done by the migrating larvae is permanent.

If larvae are seen in the retina, it is sometimes possible to destroy them through laser therapy. But, again, much of the damage is permanent and eyesight may or may not improve.

Raccoons in rehabilitation, or otherwise confined should be treated every 1-2 weeks for 3-4 treatments with any of the common wormers used to treat roundworms in dogs, e.g., piperazine, pyrantel pamoate, and fenbendazole. The efficacy of ivermectin is unknown.

What can be done to prevent dogs and humans from becoming infected?

Remember that the eggs must be in the environment 3-4 weeks before they are infective. So, fresh raccoon feces do not contain infective eggs. Infective eggs are found in fecal material that is already disintegrating and may be less obvious in the environment. Like eggs of the roundworms of dogs and cats, B. procyonis eggs can survive for years in the environment and are resistant to all common disinfectants.

Keeping raccoons as pets can pose a significant health hazard. Raccoons being rehabilitated or confined for other reasons should be on a worming program as described above. Human and domestic animal access to areas where raccoons are confined should be restricted. Raccoons should be quarantined away from other animals in cages that can be easily cleaned and decontaminated. Cages used by raccoons should not be used for other species.

Raccoon feces should be removed and destroyed daily. Individuals cleaning the cages should wear gloves and rubber boots. Protective coveralls should be worn and washed in near boiling water and bleach.

Small contaminated areas can be treated with a 50:50 mixture of xylene and ethanol. This is a hazardous solution and should only be used by trained individuals. Solutions of bleach will NOT kill the eggs, but will remove their sticky protective coats. Large areas of contamination are best decontaminated using a portable propane torch.

When cleaning areas that may have been contaminated with raccoon feces, such as haylofts, fireplaces, and attics, use disposable clothes, gloves, and a dust mask. Removed material should be burned. Do not use contaminated straw on gardens. Building a hot fire in a fireplace can decontaminate the fireplace and chimney. Chimney caps are advised to prevent raccoons from gaining access.

References and Further Reading

Georgi, JR; Georgi, ME. Canine Clinical Parasitology. Lea & Febiger. Philadelphia, PA; 1992;167-170.

Hendrix, CM. Diagnostic Veterinary Parasitology. Mosby, Inc. St. Louis, MO; 1998;121-122, 289-290.

Kazacos, KR; Boyce, WM. Baylisascaris larva migrans. Zoonosis Updates. American Veterinary Medical Association. 1995;20-30.

Kazacos, K. The ascent of Baylisascaris procyonis. In Zoonotic Larval Nematode Disease Syndromes. Veterinary Forum. November 1996;40-41.

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