Raccoon Roundworm (Baylisascaris procyonis) Survey 

The common raccoon roundworm is a close relative of the dog and cat roundworm (Toxocara canis and T. cati) and has a similar life cycle.  The adult worm lives in the raccoon's intestines with the female producing thousands to millions of eggs per day.  The eggs, passed in the host's feces, become infective in 14 to 30 days and may survive from months to years. 

Although this parasite is relatively harmless to the raccoon, serious illness can occur in humans when infective (embryonated) eggs are accidentally ingested.  Ingested eggs hatch in the small intestine, penetrate the intestinal wall and migrate to the liver via portal circulation and subsequently to lungs and other tissues via systemic circulation.  If larvae migrate to the eye, brain, or spinal cord, there can be severe and irreversible damage due to mechanical damage and inflammatory reactions.  Ocular larval migrans, most common in adults, can cause blindness.  Neural larval migrans may cause nervous system disease or death. 

Fortunately, the incidence of human illness in the U.S. is low (less than 30 cases have been reported).  Young children are the most likely individuals to become infected as they commonly put dirt and other objects into their mouths.  While not a reportable illness, the CDC receives over 4,000 requests annually for laboratory testing for this parasite. 

In June 1999, a study to determine if Baylisacaris procyonis was present in the raccoon population living in the Truckee Meadows was conducted.    Investigators from Washoe County District Health Department, Vector-Borne Diseases and the Department of Agriculture, Animal Disease & Food Safety Laboratory conducted the survey.  Samples were collected and tested from May 2001 through August 2002.  Specimens included 38 fecal samples and 4 raccoon carcasses.  Parasite identification was performed by the ADL.  Fourteen of the 38 fecal samples were positive for B. procyonis ova and 3 of the 4 raccoons necropsied had adult worms present.  Overall, this is an infection rate of 40.5% of samples tested.  Locations for all samples were recorded using a Garmin^® “GPS 12 Map” and plotted using ArcView^® 3.2 software (see map attached).  The area surveyed ranged from Verdi to Vista along the Truckee River corridor and from Lemmon Valley in the north to Incline Village at Lake Tahoe.  As the maps shows, this parasite is well established in the Truckee Meadows area.

Courtesy of Mike Murray, Washoe County District Health Department, Vector-Borne Diseases Program; Gretchen Nelson and Mark Smith, AD&FSL

Useful Links:

CDC, Emerging Infectious Diseases - Baylisascaris procyonis: An Emerging Helminthic Zoonosis

CDC, Parasitic Disease Information - Baylisascaris Infection

CDC, Parasitic Disease Information - Baylisascaris Infection (pdf)

CDC, Parasitic Disease Information - Baylisascaris Infection Fact Sheet

International Veterinary Information Service

Medical College of Wisconsin, HealthLink - Baylisascaris Procyonis