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Raccoon Roundworm
(Baylisascaris Procyonis)

raccoon roundworm life cycle

The information in blue gives a quick overview, while the black text provides more detail.

Raccoon Roundworm
Raccoons are the normal host for the parasitic nematode or roundworm known as Baylisascaris procyonis. It is the common large roundworm found in the small intestines of raccoons. Cotton rats are believed to be a possible intermediate host. Adult raccoons are susceptible only to larvae from rodent tissue while young raccoons are susceptible to infection by egg ingestion where larva hatches in small intestine with migration apparently limited to wall of small intestine. This roundworm is zoonotic, meaning it can pass from animal to animal (or human). In the raccoon, these worms normally produce no symptoms in the infected host raccoon, other than possibly intestinal obstruction, and apparently do little or no harm to adult raccoons. In the Midwest, prevalence is 70% for adult and 99% for baby raccoons according to the University of Missouri College of Veterinary Medicine. Adult worms measure 15 to 20 cm in length and 1 cm in width, tan-white in color, cylindrical and tapered at both ends. The eggs are ovoid, brown, with finely pitted outer shell, measure 70 x 55 microns and are passed in one-cell stage. The eggs embryonate into larva outside of host.

The disease is spread through the eggs contained in the feces of an infected raccoon, by ingesting either raccoon feces or things that have been in contact with raccoon feces. Adult female roundworms produce thousands to millions of eggs per day. After the eggs are shed in feces, they embryonate into a larval stage in about 3-4 weeks. They remain viable in the environment for months to over 5-6 years. When ingested, the larva migrate and reach lengths of 1.5 to 2.0 mm.

Signs and Symptoms
Clinical and pathological symptoms occur when an abnormal host (an animal other than the raccoon) becomes infected. It can cause a very rare disease called visceral larva migrans (VLM) in humans and other animals, as well as ocular larva migrans (OLM) and neural larva migrans (NLM). If ingested by an abnormal host, the eggs penetrate the small intestine (which they apparently do not do in raccoons) and undergo an aberrant migration through the body. The eggs hatch, and the larvae migrate to the brain, eyes and other organs. The parasite has been implicated in cases of serious eye disease or central nervous system disorders and infection can cause death or paralysis depending on the location in the body and number of worms.

Human toxocarosis via pets vs. Baylisascaris
It should be noted that visceral larva migrans and ocular larva migrans in humans (and other animals) can also be caused by feces of other animals - most notably pet dogs and cats. Human infection with the toxiocaris larvae of canine or feline roundworms is known collectively as toxocariasis. All cases of toxocariasis come from pets, according to the Texas Dept. of Health, Div. of Zoonosis Control, which states an estimated 10,000 new cases of roundworm infection occur in children every year, most often as a result of eating dirt contaminated with animal feces. Most human infections are mild enough to go unnoticed and apparently produce no permanent damage. However sometimes infection results in severe and even fatal disease. Common symptoms include abdominal pain, headache, weakness, lethargy and wheezing. Due to the public health significance, it is important to distinguish Baylisascaris from Toxocara. Not to minimize the risk, but in many states raccoons are being systematically euthanized because of the panic over perceived danger of transmission of the raccoon roundworm to humans as a result of two documented cases (one a fatality) to date, including a case in 1998 where a child in Pacific Grove, California was infected by eating bark on firewood that had been contaminated by raccoon feces. Over 177 local wild raccoons were systematically executed before a lawsuit by the City's concerned citizens brought the killings to a halt. Eradication of raccoons will not prevent the very rare disease visceral larva migrans in humans. However, education and some common sense might.

Contact with wild raccoons or exposure to their feces should be avoided. Hunters, trappers, and wildlife rehabilitators should wash their hands after handling raccoons. Wild raccoons should be discouraged from inhabiting buildings or other areas used by humans. Prevention also consists of never touching or inhaling raccoon feces, using rubber gloves and a mask when cleaning cages (or attics, etc.) which have been occupied by raccoons, burying or burning all feces, keeping children and pets away from raccoon cages and enclosures, and disinfecting cages and enclosures between litters. All cages and nest boxes used for housing raccoons should not be used for any other animals. They should remain strictly for raccoon use. Do frequent fecal screens on all raccoons in your possession. If positive, your wildlife vet may recommend de-worming your raccoon via treatment with an anthelmintic such as Panacur (brand of Fenbendazole) at .1 cc per pound of body weight each week until release or other accepted treatment. Remember that raccoons may have fecal matter on their paws and bodies and take appropriate safeguards. As a precaution, all my raccoons when taken into rehab receive de-worming under our vet's supervision. And, in order to guard against Human toxocariasis, have all pets (dogs and cats particularly) de-wormed under a vet's supervision and take the same precautions with their feces.

While there is no known treatment for VLM or NLM, there are several drugs that can treat the parasite in raccoons. They include piperazine, pyrantel pamoate, or fenbendazole. Following is an abstract from a study testing the efficacy of six anthelmintics against luminal stages of Baylisascaris procyonis in naturally infected raccoons (Procyon lotor) [JOURNAL. Bauer, C; Gey, A. Veterinary Parasitology, v.60, n.1-2, 1995:155-159] "Abstract: The efficacy of six anthelmintics against natural infections of Baylisascaris procyonis in raccoons (n = 7 per drug) was determined in a series of critical tests. The drugs were given via moist cat food as a single dose or once daily for three consecutive days. Raccoons treated with pyrantel embonate (1 times 20 mg base kg-1 bodyweight (bwt.)), ivermectin (1 times 1 mg kg-1 bwt.), moxidectin (1 times 1 mg kg-1 bwt.), albendazole (3 times 50 mg kg-1 bwt.), fenbendazole (3 times 50 mg kg-1 bwt.) or flubendazole (3 times 22 mg kg-1 bwt.) expelled 1-198, 2-24, 2-14, 3-80, 2-70, or 2-35 B. procyonis stages, respectively, within the faeces. No roundworm was detected in any raccoon at post mortem examinations 7 days after the end of treatment. These results suggest that any of the six anthelmintics can be used at the dose rates tested in a deworming programme for captive raccoons."

Conclusion and Opinion
When it comes to Baylisascaris procyonis, prevention and common sense should be used. Attempts to eradicate raccoon populations will not eradicate the problem and, particularly if the cotton rat is an intermediate host, may only compound it by removing a natural predator of the cotton rat. Further, it may upset the balance of nature, causing an unnatural increase in the skunk population, a reservoir of the non-raccoon strain of rabies, by removing a natural predator of baby skunks. All animals (human, domestic and wild) harbor parasites that can be transmitted to each other. Instead of panicking over a real but very rare danger, learn how to minimze the risks of transmission. And don't eat any poop.

References/Further Resources:
Baylisascaris vs. Toxocara - University of Missouri College of Veterinary Medicine
toxocariasis - Texas Dept. of Health, Div. of Zoonosis Control
Baylisascaris procyonis - Michigan DNR Wildlife Division
Baylisascaris procyonis - University of Missouri College of Veterinary Medicine
Enlightened response - Pacific Grove School District
Anthelmintic Drugs - University of Missouri College of Veterinary Medicine

Credits/Special Thanks:
Special thanks to Damon Swanson for researching and providing resources utilized in this document.

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And now for the 20th century's contribution to legalese - THE DISCLAIMER:
Anything hereinbefore or hereinafter to the contrary notwithstanding, we are neither medical doctors nor veterinarians and do not practice medicine or give medical advice. While we are licensed rehabbers through and with a wildlife rescue group comprised of all volunteers, this website is our own personal undertaking. Any suggestions presented here are NOT intended as medical or technical advice and is the result of our own experiences or information gathered from various sources, veterinarian experiences, autobiographies of raccoons we have known, and personal opinions formed from these experiences and information. It is NOT intended to take the place of medical, veterinary or professional consultation or common sense. Do not fold, spindle or mulitate. Dry clean only. We cannot guarantee the accuracy of this information (or any spelling errors not found by spellcheck). This information is being posted in good faith, as a public service, with no commercial interruptions, in cinemascope, with the belief that people will gain useful knowledge and benefit from it. No warrantees or guarantees are implied or expressed, no refunds or exchanges without original dated sales receipt and applicable shipping and handling fees, and The Gable's Raccoon World and this author shall not be liable or responsible for anyone relying upon the contents hereof, or anyone hereof contented upon lying. Printed on recycled bytes. Any additions or corrections to the information contained here is most welcomed.

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