I recently had a patient present at the clinic for an eye exam. While there the owner commented that she had bathed her dog because he had rolled in some raccoon feces prior to his appointment. Her statement gave me cause for concern so after the exam I spent a few minutes explaining the dangers of the raccoon roundworm Baylisascaris procyonis. Let me summarize our conversation here.
B. procyonis is a type of roundworm frequently spread in raccoon feces. Virtually all roundworms have a unique life cycle adapted specifically to the species of mammal they infect, known as the definitive host. Upon ingestion of an infective egg the roundworm hatches in the stomach upon which the larvae migrates to the liver. After maturing for a period of time in the liver it migrates to the lungs after which it is coughed up, re-swallowed, and settles in the small intestine. In the small intestine it attaches to the intestinal wall where it fully matures into an adult, mates and produces eggs that will be defecated out in feces thereby exposing other animals.
As you might imagine roundworms have the potential to cause significant disease in definitive hosts, and depending on the level of infection can cause the death of infected individuals. The potential for harm increases exponentially when roundworms infect individuals for which they are not specifically adapted (aberrant hosts). B. procyonis is a perfect example of the devastating effects that these parasites are capable of causing in aberrant hosts.
When B. procyonis eggs are ingested by humans, who are aberrant hosts, the larval migration never stops, resulting in a condition is called larval migrans. Liver damage can be extensive enough to cause live failure, but the harm may not stop there. B. procyonis worms may also migrate to eyes resulting in blindness and to the brain resulting in serious disability and in some instances death.
Raccoons eliminate in latrines that they create1. Infected animals shed ≈20,000 eggs/g of feces, therefore the parasite burden can be very high in and near latrines1. When these latrine areas are in close proximity to people the potential for human infection is high1.
Please take time to protect yourself and your family from infection with this potentially deadly parasite. Begin by making your home less attractive to occupation by raccoons and raccoon latrines. These extremely adaptable peridomestic animals, have made themselves very comfortable living in close proximity to humans. As omnivores they readily eat a wide variety of food including pet food, garbage and bird seed. If you feed any of your pets outside pick up food after they have eaten and clean up bird seed if you have a feeder in your yard. Make sure that garbage cans are stored in your garage or have a lid that will lock securely in place1.
Learn to recognize raccoon feces and latrines so that you can remove as soon as possible. “In urban and suburban areas, raccoons establish latrines on rooftops, in attics, in and around chimneys, and on other roof protrusions, stumps, woodpiles, decks, and lawns, especially near trees2.” Raccoon feces look very similar to canine or feline feces but often contain partially digested fruit or seeds. Basically any stray fecal material should be remove and disposed of at your earliest opportunity regardless of the species responsible.
As dogs can become infected with B. procyonis and shed eggs in their feces, administer one of the monthly broad spectrum anti-parasite medications available from your veterinarian. While none of these medications are labeled for treatment or prevention, it is generally accepted that they should have efficacy against B. procyonis. Submitting at least a yearly fecal parasite screen to your family veterinarian is a good screening test to see if your dog is infected.
For more specific advice tailored to your situation call your family veterinary provider. As this is a largely preventable condition it would be a shame for anyone that you care about to suffer from larval migrans.
1. Emerging Infectious Diseases Vol. 15, No. 9, September 2009 page 1530-1531 L. Kristen Page, Chris Achor, Ellen Luy, Sarah Kron, Grace Larson, Lauren Madsen, Kenneth Kellner, and Timothy J. Smyser.
2. Raccoon roundworm eggs near homes and risk for larva migrans disease, California communities. Emerg Infect Dis [serial online] 2003 DecRoussere GP, Murray WJ, Raudenbush CB, Kutilek MJ, Levee DJ, Kazacos KR.