Baylisascaris

By: Allison Hawkins

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What is it?

Baylisascaris infection is caused by a roundworm found in raccoons. This roundworm can infect people as well as a variety of other animals, including dogs. Human infections are rare, but can be severe if the parasites invade the eye (ocular larva migrans), organs (visceral larva migrans) or the brain (neural larva migrans).

Risk Factors

While raccoons are the roundworm's primary host, other types of animals can become infected. Birds and small mammals, such as rodents and rabbits, are susceptible to the parasite. Unlike raccoons, these animals sometimes show signs of infection, such as muscle spasms, tremors, and progressive weakness; infection can lead to death. Predator animals, including dogs, may become infected by eating an animal that has been infected with Baylisascaris. In some dogs, Baylisascaris may develop to adult worms and pass eggs in the dogs' feces.

The worms develop to maturity in the raccoon intestine, where they produce millions of eggs that are passed in the feces. Eggs that are excreted by raccoons are not immediately infectious. These eggs must develop in the environment for 2 to 4 weeks, after which the eggs are able to cause infection. The eggs are resistant to most environmental conditions and with adequate moisture, can survive for years.


Humans become infected by ingesting embryonated (fertile) eggs. Anyone who is exposed to environments where raccoons frequent is potentially at risk. Young children or developmentally disabled persons are at highest risk for infection as they may be more likely to put contaminated fingers, soil, or objects into their mouths.

Hunters, trappers, taxidermists, and wildlife handlers may also be at increased risk if they have contact with raccoons or raccoon habitats.

Fewer than 25 cases of Baylisascaris disease have been documented in the United States. However, it is possible that some cases are incorrectly diagnosed as other infections or go undiagnosed. Cases that are diagnosed tend to be severe.

Cases have been reported in California, Illinois, Louisiana, Massachusetts, Michigan, Minnesota, Missouri, New York, Oregon, and Pennsylvania. As of 2012, there were 16 published human neurological cases in the US; six of the infected persons died.


Signs & Symptoms

People become infected when they accidentally ingest infective eggs in soil, water, or on objects that have been contaminated with raccoon feces. Baylisascaris infection is not spread from one person to another. When humans ingest these eggs, they hatch into larvae in the person's intestine and travel throughout the body, affecting the organs and muscles.

Depending on where the larvae migrate, Baylisascaris infection can affect the brain and spinal cord (neural larva migrans), the eye (ocular larva migrans), and/or other organs (visceral larva migrans).

Signs and symptoms depend on how many eggs are ingested and where in the body the larvae migrate (travel). Ingesting a few eggs may cause few or no symptoms, while ingesting large numbers of eggs may lead to serious symptoms. Symptoms of infection may take a week or so to develop and may include:

  • Nausea
  • Tiredness
  • Liver enlargement
  • Loss of coordination
  • Lack of attention to people and surroundings
  • Loss of muscle control
  • Blindness
  • Coma

Treatment

No drugs have been shown to be totally effective for the treatment of Baylisascaris infection. Albendazole, a broad spectrum anthelmintic, has been recommended for specific cases.

Early treatment might reduce serious damage caused by the infection. Should you suspect you may have ingested raccoon feces, seek immediate medical attention.