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Other Names: Raccoon Roundworm Infection, Baylisascariasis

Baylisascariasis is a zoonotic infection caused by larvae of raccoon roundworm, Baylisascaris procyonis (found in raccoons and dogs), and sometimes B. columnaris (found in skunks), and B. melis (found in badgers).

In raccoons, adult worms live in the small intestine. When eggs laid by the female worms are passed in feces and reach the ground, under ideal conditions of humidity and temperature it takes a minimum of about 2 weeks for the first-stage larvae to form. Female worms can produce between 115,000 and 179,000 eggs per day per worm; therefore, infected raccoons can shed millions of eggs per day in their feces. Even after the feces has dissolved, the roundworm eggs will remain viable in the environment for several years, even when exposed to freezing temperatures.

Chickens become infected by accidental ingestion of embryonated eggs that are present in the environment, shed from the feces of raccoons, dogs, and other carriers. Once the eggs are eaten, larvae are released, which penetrate the intestinal wall and migrate through the bloodstream to reach other organs and tissues, including the Central nervous system (CNS) and eyes.
Raccoon Roundworm Life Cycle Chickens
They then settle and become encapsulated in granulomas in various organs and tissues, resulting in sudden onset of neurological signs such as head tilt, and paralysis.

Clinical Signs

Head tilt (wry neck)
Incoordination (ataxia)
Paresis to Paralysis
Difficulty perching


  • History
  • Clinical signs
  • Physical exam
  • Fecal test
  • Tissue biopsy

Reported Cases

  • Case 1: Baylisascariasis in a Chickens Ascarid (roundworm) migration was the cause of sudden onset of neurologic signs – head tilt and left side paresis in a 6-week-old chicken. A large granulomatous lesion was observed in the brain stem with a cross-section of an ascarid-like parasite in the center. Granulomatous lesions were also seen in the lungs. The submitting veterinarian indicated the owner had a problem with raccoons. Baylisascaris procyonis is a ubiquitous roundworm in raccoons and when the roundworm eggs are ingested by other hosts (including children), larvae develop from the eggs and migrate through the internal organs, frequently penetrating the brain. Keeping chickens, children and other animals away from raccoon fecal material is extremely important. Ref

  • Case 2: Baylisascariasis in a Chickens A flock of 50 chickens were experimentally infected with Baylisascaris procyonis roundworms. 34% (17 of the birds) showed clinical signs of central nervous system dysfunction an average of 20.4 days post infection. Signs observed included wry neck (torticollis), ataxia, circling, extensor rigidity, and paralysis. Some birds progressed rapidly to prostration and death, while others lived for as long as 23 days while exhibiting CNS signs until they were killed. The groups who received the highest dosages showed more severe signs. Ref

  • Case 3: Baylisascariasis in a Chickens A flock of 11,000 four-week-old white leghorn pullets suddenly started showing signs of ataxia, paralysis, wry neck (torticollis), circling, and rolling, over a course of 3-5 weeks post exposure. In some chickens, the signs progressed to prostration followed by death. An investigation into the management of the flock revealed that a family of raccoons were living where the straw that was used as bedding for the chickens was kept. Large quantities of raccoon feces were found covering the straw, and Baylisascaris procyonis eggs were recovered from a fecal exam. Ref

  • Case 4: Baylisascariasis in a Cockatoo An adult female Moluccan cockatoo was evaluated for a 10-day history of progressive ataxia and weakness. The bird had been exposed intermittently over a 3-day period to a cage that had previously housed juvenile raccoons. Results of diagnostic tests were inconclusive and, despite supportive care, the bird died 7 days after the initial presentation. Histopathologic examination revealed a single nematode larva in the midbrain that was consistent with Baylisascaris species and multifocal granulomas in the left ventricle of the heart. The neurologic disease in this bird was attributed to encephalitis caused by neural larval migration of the raccoon roundworm, Baylisascaris procyonis. Ref

  • Case 5: Baylisascariasis in a Macaw Seven out of 10 birds in a mixed group of blue and gold macaws, scarlet macaws, and hybrid macaws developed ataxia, torticollis, and depression after being placed on an island exhibit accessible to raccoons. Larvae of Baylisascaris procyonis were found in cerebrospinal tissue from six of the macaws. Ref

  • Case 6: Meningoencephalitis in a Quail Severe nonsuppurative meningoencephalitis with multifocal areas of malacia was diagnosed as the cause of a progressive neurological disorder in a flock of 85 bobwhite quail. The histologic alterations were shown to be associated with the larval migration of the common roundworm of raccoons, Baylisascaris procyonis. Ref


Supportive care: Isolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.:



  • Discouraging raccoons, skunks, or badgers from entering areas where chickens forage.
  • Don't let dogs defecate in areas where chickens roam.


Usually fatal

Scientific References


Risk Factors

  • Raccoons, skunks, bears, badgers, or dogs living near the premises of where chickens are kept.