Humans can contract this parasite through the ingestion or inhalation of the round worm eggs.

Roundworm (Baylisascaris procyonis) is a common intestinal parasite of raccoon and is a cause of a fatal nervous system disease in wild animals. Raccoon roundworm is not new and its occurrence in raccoons ranges from 40-60% in adults and 90-95% in juveniles.

Raccoon roundworm begins when an egg is deposited by an adult worm living in the intestine of an infected raccoon. The microscopic eggs are shed in the feces, and a single defecation may carry anywhere from a few thousand to more than 10 million eggs!

Raccoons tend to defecate in localized areas over a period of time. These "latrines" are located at the base of trees, in barn lofts, woodpiles, attics, chimneys, sandboxes or elevated surfaces such as logs or rocks.

Young raccoons become infected by ingesting eggs that are present in contaminated areas around den sites and adult raccoons become infected by eating intermediate hosts (mice, rats, chipmunks, weasels, woodchucks, squirrels, birds, rabbits) that have the larvae encysted in their tissue.

Life cycle

After the eggs are deposited, they become infective in about 30 days after they are shed. An intermediate host (an animal in which the parasite lives, but does not develop into adult worms) plays an important role in the life cycle of this parasite. Once ingested by an intermediate host, (mice, chipmunks, birds, rats, foxes, rabbits, beaver, humans, etc) the eggs hatch into larvae which burrow through the wall of the host's intestine and migrate to the liver and lungs. From the lungs, the larvae migrate to tissues throughout the body (head, neck and chest), although they tend to migrate to the central nervous system and the eyes. They stop migrating within a few weeks and then encapsulate within the intermediate host's tissue. The disease is dosage dependent; meaning the more eggs ingested, the more damage to the intermediate host.

Once encapsulated, the worms generally cause no further problems for the host. Only migrating larvae are damaging or deadly. When the intermediate host dies, and is eaten by a raccoon, the cysts open and grow in to egg-shedding adult roundworms in the intestine of the raccoon, starting the cycle all over again.

Roundworm Eggs

The eggs of the raccoon roundworm are some of the most resistant parasites known. The outer covering is sticky and will stick to any type of surface. They are resistant to disinfectants and antiseptics and will continue to contaminate an area for a very long time. Eggs have been known to survive 8-10 years under laboratory conditions and several years in soil during harsh winters. The most effective way to destroy the eggs is through incineration.

Signs and Symptoms

Raccoon round worm is relatively harmless to the raccoon. Infected raccoons may appear normal and show no signs, but death may result due to intestinal blockage or rupture in cases of heavy parasite infection.

The clinical signs of this disease in the intermediate host may resemble those of rabies and caution should be taken. Central nervous system disorders include head tilt, stumbling, circling or paralysis. Depending on the size of the host and the number of eggs ingested, these symptoms may develop in 1-3 weeks. When the disease progresses, the animal may lose its fear of humans and become aggressive. Eventually the animal becomes comatose and dies. Death may occur as soon as 3-5 days after clinical signs begin or as long as 2 months.

Humans can contract this disease only through the ingestion or inhalation of the roundworm eggs. The presence of raccoons s not an imminent threat as far as exposure to this parasite, rather it is the presence of feces and contaminated nesting material.

In humans, the disease is difficult to diagnose. Children are most susceptible to this parasite since they are more apt to place contaminated objects or soil in their mouth. The presence of larvae or the lesions caused by them in the eye are signs most readily seen by a physician. Symptoms may include drowsiness, confusion, loss of muscle coordination or decreased head control. Humans may have permanent nervous disabilities or vision loss and in severe cases, blindness or death may occur.

In suburban areas, raccoons may occur in higher densities. It is important that people make their property less attractive to raccoons by eliminating potential den sites and food sources.

Follow precautions to reduce your risk of exposure and infection

  • Don't keep raccoon as pets-it's against the law in Massachusetts
  • Avoid feeding raccoons
  • When sweeping dry raccoon feces from attics, basements, barns etc, wear disposable gloves and a protective mask to prevent inhaling eggs
  • Burn dry feces and contaminated material (hay and straw) if possible
  • Don't use raccoon feces as a garden fertilizer
  • Screen/cap chimneys appropriately " Block holes and access to attics, under sheds, porches, decks and other buildings
  • Secure animal feeds and bedding from being contaminated by raccoon feces "
  • Hunters/Trappers should wash hands after handling raccoons
  • Use caution with firewood that raccoons may have used as latrines
  • Cover children's sandboxes to keep animals from using them as latrines

To Clean Contaminated Areas -- Washing with bleach will remove the sticky outer covering on the egg but will not destroy the egg. To destroy the egg you must use boiling lye or propane torching.


This information was prepared through the cooperation of: Mass. Department of Fisheries Wildlife and Environmental Law Enforcement and the Northeastern Research Center for Wildlife Diseases, University of Connecticut/Storrs


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Another agency with information on animal diseases is the Massachusetts Department of Public Health.


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