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Raccoon Roundworm Infection ("Baylisascaris procyonis") in Humans

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Roundworm in wildlife and pets

Roundworm in wildlife and pets

Can Humans Get Raccoon Roundworm?

Raccoon roundworm can be acquired by humans from an environment if safety precautions are not taken. I used to rehabilitate raccoons and was required to wear special safety glasses, masks, and booties for risk of exposure when cleaning out their enclosures.

It's important to note that raccoon roundworm or the Baylisascaris procyonis parasite is different but similar to the canine roundworm or Toxocara canis. Canine roundworm can be cleared with routine prevention, whereas raccoon roundworm causes serious neurological symptoms in dogs, humans, etc.

Raccoon roundworm lifecycle. Sourced from the CDC.

Raccoon roundworm lifecycle. Sourced from the CDC.

What Is Roundworm?

Raccoons are a definitive host of Baylisascaris procyonis, a parasitic roundworm of zoonotic potential; zoonosis implies the ability to infest humans. Raccoons are peridomestic (habituated to people) and therefore carry the parasite in close proximity to humans, dogs, and cats. Birds and small mammals act as intermediate hosts for raccoon roundworm as well humans. B. procyonis, however, cannot complete its life cycle in the human body.

Note: Infestation is generally used to refer to disease-causing parasites, whereas infection is used to refer to disease-causing microorganisms (bacteria, viruses).

Roundworm may be deposited in soil.

Roundworm may be deposited in soil.

Where Is Roundworm Found?

Roundworm is found throughout the United States (North America), Europe, and Japan—specifically the midwestern and northeastern states and the west coast. It is not commonly found in the southern states.

Where Do Raccoons Like to Live?

Raccoons are a species well-adapted to urban, suburban, and rural settings. They often scavenge for food sourced from garbage cans, bird feeders, and pet food. Raccoons seek out:

  • Lofts
  • Attics
  • Chimneys
  • Wooden decks
  • Woodpiles
  • Patios
  • Basements
  • Sandboxes
  • Ponds

Because raccoons seek out human-made constructions for residency, this puts them in proximity to humans and canine companions.

Sources of Contamination

Raccoons take to latrines (the deposit and accumulation of feces and urine). Raccoon feces are dark, tube-shaped, and have a pungent odor. The feces contain bones, fruits, vegetables, and scavenged bits of garbage.

Roundworm may accidentally be ingested orally if good hygiene is not practiced.

Roundworm may accidentally be ingested orally if good hygiene is not practiced.

How Can You Get Roundworm From Your Pets?

Young children are particularly at risk of an infestation, as are dogs. Soil, water, and objects that are contaminated with fecal material and roundworm eggs are direct sources. Ingestion is the most common method of transmission via hand-to-mouth (or the consumption of contaminated soil, fruits, and vegetables).

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The eggs are hardy and can survive in the environment and stay viable and infective for years. Eggs take two to four weeks to embyronate and become infective. 20,000 to 26,000 eggs are shed in each gram of feces (in the millions daily).

What if My Dog Has Roundworm?

Dogs can be infected and not show signs. Deworming of your pet is necessary for prevention. Common dewormers include pyrantel pamoate and fenbendazole. Dogs can shed the eggs or harbor a patent infestation (sexually mature adult infestations). Dogs are also indiscriminate defecators, so their stool may be distributed throughout the yard and pose a risk to humans.

What Are the Signs and Symptoms of Roundworm in Humans?

The roundworm is known to migrate (neural larva migrans). In humans, the large and hardy worms hatch in the small intestine, penetrate through the lungs and enter systemic circulation via the left side of the heart. The liver, heart, lungs, brain, eyes, spinal cord, and other organ tissues are concurrently damaged. Dogs are infected in a similar manner. Common symptoms in humans include:

  • Lethargy
  • Nausea
  • Hepatomegaly (enlarged liver)
  • Coordination issues
  • Disorientation
  • Muscle spasms
  • Blindness
  • Lung complications (cough, chest pain)
  • Photophobia, retinitis, blindness
  • Eventual comatose

Host inflammation does little to protect or cure the infestation. The larger a load of ingested embryonated eggs, the more dangerous the infestation, thus leading to permanent disability and death.

Signs of infestation are based on the load ingested and can take one to four weeks to present.

  • In the raccoon: Infestation in the raccoon is subclinical (the adult, tan-colored worms are confined to the small intestine).
  • In the human: Infestation in humans can be devastating. The roundworm migrates ocularly, viscerally, and neurally. Central nervous tissue is invaded by the growth of larvae and neurologic survivors have not been documented. Infestation in infants/children are fatal.
The parasite is often detected under a microscope.

The parasite is often detected under a microscope.

How Is Roundworm Diagnosed in Humans?

Early treatment is necessary and diagnosis is difficult; a commercially available serological test does not exist. Other diagnostic methods include:

  • Positive antibody titers (testing of CSF and serum)
  • Ocular diagnosis may occur as worms migrate into the eye
  • Neuroimaging (an MRI may be used to detect white matter abnormalities)
  • Biopsy
  • Encephalography

How Is Roundworm Treated?

Prevention is key. A broad-spectrum anthelmintic may be administered. These include:

  • Albendazole treatment
  • Mebendazole
  • Ivermectin
  • Corticosteroids used in conjunction with albendazole

Note on Raccoon Extraction

Raccoon extraction should be handled by a professional using humane methods. The removal of raccoon waste is also best handled by a professional due to the high risk of zoonotic disease. Do not risk your health and safety.

How to Get Rid of Raccoon Waste in the Yard

Remove the aforementioned habitats (wood piles, etc.) and prevent access to food sources and water near public areas. If you come across a potential raccoon latrine or find raccoon feces, remove the feces as soon as possible (2-4 weeks needed for eggs to become infective).

Burn, bury, scorch (controlled propane torch), or scour (with boiling water) any contaminated surfaces. Wear gloves, disposable booties, rubber boots, avoid creating dust, and wear an N95 respirator. Decontaminating sites for canine companions and humans alike is the best method of prevention.


  • Gavin, Patrick J., and Kevin R. Kazacos, Stanford T. Shulman. "Baylisascariasis." Clinical Microbiology Reviews 18.4 (2005): 703–718. Accessed 9 March 2016.< articles/PMC1265913/>.
  • "Parasites–Baylisascaris infection." Centers for Disease Control and Prevention: Global Health–Division of Parasitic Diseases and Malaria. Revised 11 October 2012. Accessed 3 March 2016. < baylisascaris/geninfo/index.html>.
  • Foster and Smith. "Baylisascaris procyonis (Raccoon Roundworm)." Veterinary and Aquatic Services Department Accessed 2 March 2016. < article.cfm?c=2+1621&aid=721>.

This content is for informational purposes only and does not substitute for formal and individualized diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed medical professional. Do not stop or alter your current course of treatment. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2018 Laynie H

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