Baylisascaris procyonis

What is Baylisascaris procyonis?

This is a large roundworm parasite that lives in the intestines of raccoons. The worm does not harm the raccoon, but on rare occasions can cause serious illness in humans. About half of all raccoons tested in Wisconsin have been found to be infected. Raccoons throughout the state have been shown to be infected with Baylisascaris procyonis, but the parasite is more prevalent in the southern portion of Wisconsin.

How is this raccoon roundworm spread?

The adult worms shed microscopic eggs that are passed in the raccoon's feces. Millions of eggs may be passed each day. These eggs can survive for months to years in the environment. The parasite is transmitted when the eggs are ingested by another animal. Humans generally become infected from accidentally ingesting eggs from soil, water, hands, or other objects which are contaminated with raccoon feces.

What are the signs and symptoms of Baylisascaris procyonis in humans?

The severity of the disease depends to a large extent on how many eggs are ingested. These eggs hatch into larvae which then cause disease by migrating through the central nervous system, eyes, and other organs. Symptoms include nausea, lethargy, liver enlargement, incoordination, loss of muscle control, coma, and blindness. Fatalities are rare, but have been reported. There have been no human cases reported in Wisconsin.

How soon after infection do symptoms appear?

In general, symptoms appear one to three weeks post-infection, although they may take as long as two months. This interval depends on the number of eggs ingested.

Who is at greatest risk for Baylisascaris procyonis infection?

Because of young children's tendency to put their fingers or objects into their mouths, they are at risk if they play in areas which are frequented by raccoons. Hunters, trappers, taxidermists, and wildlife rehabilitators are also at increased risk if they handle raccoons or items contaminated with raccoon feces.

How are Baylisascaris procyonis infections treated in humans?

There are no consistently effective treatment regimens available at this time.

How can I avoid exposure to this parasite?

Do not keep raccoons as pets; this is not only dangerous, it is also illegal. Baby raccoons are often infected. Discourage raccoons from visiting your home or yard by eliminating access to food sources like garbage cans and bird feeders. Raccoons may nest in (and defecate on) places like woodpiles, attics, chimneys, sheds, and barn lofts. Entrances to these areas can be sealed when the raccoons are away. Accumulated feces and contaminated wood, soil, hay or straw should be removed and burned or deeply buried in a site remote from houses. It is important to wear disposable gloves, boots, and a dust mask (such as a painter's mask) when disposing of such material. Contaminated surfaces can be decontaminated by flaming with a propane torch (used for concrete and other non-flammable surfaces) or with boiling Lysol.

Each year, Medical College of Wisconsin physicians care for more than 180,000 patients, representing nearly 500,000 patient visits. Medical College physicians practice at Children's Hospital of Wisconsin, Froedtert Memorial Lutheran Hospital, the Milwaukee VA Medical Center, and many other hospitals and clinics in Milwaukee and southeastern Wisconsin.