Baylisascaris in Dogs

What is Baylisascaris?

Baylisascaris procyonis, also known as the raccoon roundworm, is a parasite found in the intestinal tract of many raccoons. In some cases, this parasite may also spread to dogs and cats. Although B. procyonis has similarities to the roundworm species typically seen in pets, there are also key differences that can make B. procyonis a significant health risk.

B. procyonis infections in dogs are most common in the Midwest, Northwest, and Western United States. An increasing number of cases are being seen even outside of that area, however, and the parasite’s range may be increasing.

How do dogs become infected with Baylisascaris?

Dogs can become infected with B. procyonis in two different ways.

In most cases, dogs become infected when they ingest the parasite’s eggs.

These eggs are shed in the stool of infected raccoons and, after developing for approximately two weeks in the environment, can cause infection in any animal that consumes them. Dogs may ingest raccoon roundworm eggs when they intentionally eat raccoon feces or when they lick their paws or coat after being in a contaminated environment.

Less commonly, dogs may become infected by eating an animal infected with B. procyonis. Although raccoons are the primary host of this parasite, other animals, such as rabbits, rodents and birds, may become infected by exposure to raccoon feces. If a dog eats an animal that has B. procyonis larvae within its tissues, infection may occur.

What are the clinical signs of Baylisascaris infection?

Most B. procyonis infections are asymptomatic. In some cases, large numbers of worms in the intestines may lead to diarrhea and other gastrointestinal signs.

Less commonly, however, B. procyonis may migrate from the dog’s intestines to the body’s nervous tissues. This can have serious effects. Signs of neurologic involvement may include depression, weakness, circling, head tilt, muscle tremors, paralysis, coma, and even death.

How is Baylisascaris diagnosed?

Infected dogs pass microscopic B. procyonis eggs in their feces. These eggs may be identified by your veterinarian on routine fecal parasite testing. However, the diagnosis of this parasite can be challenging, because B. procyonis eggs are very similar in appearance to other common roundworm species. Further diagnostic testing may be needed to distinguish B. procyonis from other roundworm species.

In some cases, findings consistent with B. procyonis are found during the workup of a dog with unexplained neurologic signs. Dogs with unexplained neurologic signs may undergo a cerebrospinal fluid (CSF) tap, leading to the discovery a type of inflammatory cell that can suggest the presence of parasitic infection. This may prompt further investigation that results in the diagnosis of B. procyonis.

What is the treatment for Baylisascaris?

Intestinal B. procyonis infections can easily be treated with most common dewormers. If your dog has diarrhea or vomiting due to the infection, your veterinarian may prescribe additional treatments to alleviate the gastrointestinal signs.

When B. procyonis affects the nervous system, however, treatment is often not possible. Most deworming medications do not reach the nervous tissues, so they offer limited benefits in neurologic patients. Steroids, such as prednisone, may be used to treat inflammation associated with B. procyonis and manage clinical signs, but they will not treat the parasite itself.

What is the prognosis for Baylisascaris?

Intestinal B. procyonis infections typically resolve quickly with appropriate deworming. If a dog is showing neurologic signs associated with B. procyonis, the condition is almost always fatal.

Can Baylisascaris affect humans?

Yes. B. procyonis is a zoonotic disease, which means that it can cause illness in humans. Fortunately, infections are rare. Most infections occur in young children who ingest raccoon feces or have close contact with raccoons. Clinical signs of infection in humans are similar to those seen in dogs; they can range from asymptomatic intestinal infections to severe and fatal neurologic disease.

How can I prevent Baylisascaris infection in my dog?

Given the treatment challenges associated with B. procyonis, prevention is the best strategy. Minimize your dog’s exposure risk by limiting your dog’s access to raccoons and their droppings:

  • Keep your dog on a leash or confined to a fenced yard when outdoors.
  • Do not feed raccoons or other wild animals on your property.
  • Do not leave pet food outside unattended.
  • Ensure that trash cans are properly secured.
  • Avoid keeping raccoons as pets.
  • If you find raccoon droppings on your property, clean them up immediately (while wearing gloves).
  • If you suspect your dog has come in contact with raccoon droppings, bathe your dog thoroughly (while wearing gloves).

In addition to minimizing exposure risks, be sure to keep your dog on year-round parasite prevention. Oral heartworm preventatives typically also include an intestinal dewormer that is effective against B. procyonis. Talk to your veterinarian to determine the best parasite prevention for your pet.

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