Definition of Baylisascaris

Reviewed on 6/3/2021

Baylisascaris: Infection by the raccoon roundworm. Baylisascaris procyonis is found commonly in raccoons. When infective eggs of this roundworm are ingested by humans, Baylisascaris larvae hatch in the intestine and travel through the organs and muscles. This is the larva migrans syndrome.

Infected raccoons shed millions of eggs in their feces. The eggs develop to the infective stage in 2-4 weeks. The eggs are resistant to most environmental conditions and, with adequate moisture, can survive for years. Infection is spread when eggs are accidentally ingested by a person or animal. People, especially young children, become infected from accidentally ingesting eggs from soil, water, hands, or other objects that have been contaminated with raccoon feces. The eggs must be ingested by a human or other animal to be able to hatch and release larvae. Animals may also become infected by eating a smaller animal that has been infected with Baylisascaris.

The signs and symptoms of Baylisascaris infection depend on how many eggs are ingested and where in the body the larvae travel to. Once swallowed and inside the body, eggs hatch into larvae, which then cause disease when they migrate through the liver, brain, spinal cord, and other organs. Swallowing a few eggs may cause few or no symptoms. Ingesting large numbers of eggs may lead to serious symptoms. These symptoms may include nausea, fatigue, liver enlargement, lack of coordination, lack of attention to people and surroundings, loss of muscle control, coma, and blindness. Some cases have resulted in death. Signs and symptoms of infection may take a week or so after ingestion of eggs to develop.

Anyone exposed to environments in which raccoons live is potentially at risk. Young children and developmentally disabled persons are at highest risk for infection because they spend time outdoors and they may put dirty fingers or objects into their mouths. Hunters, trappers, taxidermists, and wildlife rehabilitators may also be at increased risk if they handle raccoons or raccoon feces.

No effective cure is available. To prevent infection, avoid direct contact with raccoons, especially their feces. Do not keep, feed, or adopt raccoons as pets! Raccoons are wild animals. Discourage raccoons from living in and around your home or parks by removing access to food. Clear brush so raccoons are not likely to make a den on your property. Stay away from areas and materials that might be contaminated by raccoon feces. Raccoons typically defecate at the base of or in raised forks of trees, or on raised horizontal surfaces such as fallen logs, stumps, or large rocks. Raccoon feces also can be found on woodpiles, decks, rooftops, and in attics, garages, and haylofts. Feces usually are dark and tubular, have a pungent odor (usually worse than dog or cat feces), and often contain undigested seeds or other food items.

To eliminate eggs, raccoon feces and material contaminated with raccoon feces should be removed carefully and burned, buried, or sent to a landfill. Care should be taken to avoid contaminating hands and clothes. Treat decks, patios, and other surfaces with boiling water or a propane flame-gun. (Exercise proper precautions!) Prompt removal and destruction of raccoon feces will reduce risk for exposure and possible infection. Newly deposited eggs take at least 2-4 weeks to become infective.


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