Racoon Disease in Dogs

Baylisascariasis in Dogs

Most commonly called "raccoon disease" because of its prevalence in the raccoon population, baylisascariasis comes from contact with raccoon feces, and from ingesting animal tissue that is infected with the Baylisascaris procyonis parasite.

Commonly referred to as roundworm, the B. procyonis larvae is found in a large part of the animal population, including humans -- making this a zoonotic disease, which means that it can be spread from an infected animal to other animal species, which includes humans. Raccoons are the optimal carriers of this worm, since the health of the raccoon is not adversely affected, making it the ideal host and disseminator of the parasite. The B. procyonis larvae is typically spread through the fecal material into the environment. Any contact with the feces, or with soil that has been used by an infected raccoon, may lead to systemic infection. Therefore, it is essential to practice methods of avoidance and caution in areas where raccoons are prevalent.

Intermediate carriers are birds, rabbits and rodents, amongst other animals. The larva is known to migrate to the brain, where it affects the nervous system. In this weakened state, the small animal becomes an easy catch, and the larva is ingested when the predator animal (i.e., a dog) ingests tissue from the infected animal. This is another way in which the worm is disseminated to other animals.

This disease is known to occur throughout the United States, with reported outbreaks in zoos and on farms. However, an outbreak can occur wherever animals are kept together in large groups.

While this infection can often be treated in adult dogs, it is almost always fatal for puppies. In addition, because the worm sometimes attacks the brain and nervous system, this infection may be mistaken for rabies. If rabies is suspected, you may wish to ask your veterinarian to test for the presence of the B. procyonis.

The condition or disease described in this medical article can affect both dogs and cats. If you would like to learn more about how this disease affects cats, please visit this page in the PetMD health library.

Symptoms and Types

Two types of baylisascariasis have been reported in dogs: intestinal infection and visceral disease. The development of the roundworm begins with ingestion of the roundworm eggs. They then migrate to the intestines, where they further develop before their final migration into the viscera (the organs that occupy the abdominal cavities), the nervous system, or the eye. These types of infections are referred to, respectively, as larval migrans; visceral larval migrans (VLM); neural larval migrans (NLM); and ocular larval migrans (OLM).

The intestinal form is most commonly found in adult dogs, while infection of internal organs, particularly the brain and spinal cord (visceral disease) is more common in puppies. Often, there are not any outward symptoms associated with early onset of the disease, but occasionally dogs will show signs of neurological disease due to the worm attacking the nervous system. Signs of neurological disease (NLM) include:

  • Unsteady walking/loss of coordination or muscle control (ataxia)
  • Difficulty eating/swallowing (dysphagia)
  • Lethargy, lying down excessively (recumbency)
  • Circling
  • Seizure
  • Confusion, lack of attention

Infection of the viscera (VLM) may present symptoms of liver and/or lung disease, while infection of the eye (OLM) may not be apparent until your dog has lost the use of its vision.


The most common method of acquiring the infection originates from sharing an area with infected raccoons. A dog can become infected with the disease from coming into contact with raccoon feces, from ingestion of B. procyonis eggs, which may remain viable in the soil long after the raccoon feces has disintegrated or been removed, from ingestion of animal tissue that is infected with the roundworm (e.g., rabbits, birds, etc.), or from close contact with other infected animals.


You will need to give your veterinarian a thorough history of your dog's health, including a background history of symptoms, and possible incidents that might have led to this condition. The history you provide may give your veterinarian clues as to which organs are being affected. Knowing the path the parasite has taken is essential for treating the infection appropriately.

The intestinal form of baylisascariasis is found by examining the dog's feces, while the larval form may be found in association with other diseases such as rabies, canine distemper, and congenital neurological defects. A direct fecal smear test will detect the intestinal form of the disease, while the larval form can usually be found through an eye (ophthalmoscopic) examination, or by a laboratory examination of a tissue sample.

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