Baylisascaris infection is caused by a roundworm found in raccoons. This roundworm can infect people as well as a variety of other animals, including dogs. Human infections are rare, but can be severe if the parasites invade the eye (ocular larva migrans), organs (visceral larva migrans) or the brain (neural larva migrans).

Baylisascaris roundworms are intestinal parasites found in many different animals. Baylisascaris infection in humans is uncommon but can be severe. While Baylisascaris can infect different types of animals, Baylisascaris procyonis, carried by raccoons, is thought to pose the greatest risk to humans because raccoons often live in close proximity to humans. Humans can acquire the parasite by ingesting the eggs of infected raccoons. Young children are at greatest risk for Baylisascaris infection because they are more likely to put contaminated soil in their mouths. Though rare, human infections can be severe if the parasite invades the eye (ocular larva migrans), organs (visceral larva migrans), or the brain (neural larva migrans). Symptoms of a Baylisascaris infection may include nausea, fatigue, an enlarged liver, loss of coordination, lack of muscle control, blindness, and coma. Baylisascaris infections cannot be spread from one person to another. No drug has been found to be completely effective against Baylisascaris infections in humans though albendazole has been used in some cases.

Causal Agent

Baylisascaris procyonis, the raccoon roundworm, is a rare but serious cause of neurologic and ocular disease in humans. Only larval stages are involved in zoonotic infections. It is not known whether other Baylisascaris species, such as B. columnaris of skunks, can cause baylisascariasis in humans.

Life Cycle

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Baylisascaris procyonis completes its life cycle in raccoons, with humans acquiring the infection as accidental hosts (dogs serve as alternate definitive hosts, as they can harbor adult worms and shed eggs). Unembryonated eggs are shed in the environment , where they take 2–4 weeks to embryonate and become infective . Raccoons can be infected by ingesting embryonated eggs from the environment . Many mammals and birds can act as paratenic hosts for this parasite: eggs ingested by these hosts hatch and larvae penetrate the gut wall and migrate into various tissues where they encyst . The life cycle is completed when raccoons eat these hosts . The larvae develop into adult worms in the raccoon’s small intestine and eggs are passed in raccoon feces. Humans become accidentally infected when they ingest infective eggs from the environment . Migration of the larvae through a wide variety of tissues (liver, heart, lungs, brain, eyes) results in visceral (VLM) and ocular larva migrans (OLM) syndromes, but severe neurologic disease with eosinophilic meningoencephalitis may occur following neural larva migrans (NLM) . B. procyonis larvae continue to increase in size up to about 1.8 mm in human hosts, but they are not capable of migrating to the intestine and developing to adulthood. Tissue damage and the signs and symptoms of baylisascariasis are often severe because of the larger size of B. procyonis larvae and their more invasive course of migration.

Life cycle and information courtesy of DPDx.

What is Baylisascaris?

Baylisascaris worms are intestinal parasites found in a wide variety of animals. Different species of Baylisascaris are associated with different animal hosts. For example, Baylisascaris procyonis is found in raccoons, and Baylisascaris columnaris is found in skunks. Cases of Baylisascaris infection in people are not frequently reported but can be severe. Baylisascaris procyonis is thought to pose the greatest risk to people because of the often close association of raccoons to human dwellings.

In what parts of the world is Baylisascaris found?

Baylisascaris procyonis has been identified in the United States, Europe, and Japan. Some evidence of infection in animals has been reported in South America.

In the United States, infected raccoons have been found in a number of states, especially in the mid-Atlantic, Midwestern states and West Coast states.

How do people get infected?

People become infected by ingesting infectious eggs. Most infections are in children and others who are more likely to put dirt or animal waste in their mouth by mistake.

How can I prevent Baylisascaris infection?

Eggs passed in raccoon feces are not immediately infectious. In the environment, eggs take 2 to 4 weeks to become infectious. If raccoons have set up a den or a latrine (places where raccoons defecate) in your yard, raccoon feces and material contaminated with raccoon feces should be removed carefully and burned, buried, or sent to a landfill. Care should be taken to avoid contaminating hands and clothes. Treat decks, patios, and other surfaces with boiling water or a propane flame-gun (exercise proper precautions). Prompt removal and destruction of raccoon feces before the eggs become infectious will reduce risk for exposure and possible infection.

Do not keep, feed, or adopt wild animals, including raccoons, as pets.

Washing your hands after working or playing outdoors is good practice for preventing a number of diseases.

What are the symptoms and signs of Baylisascaris infection?

The incubation period (time from exposure to symptoms) is usually 1 to 4 weeks. If present, signs and symptoms can include the following:

• Nausea
• Tiredness
• Liver enlargement
• Loss of coordination
• Lack of attention to people and surroundings
• Loss of muscle control
• Blindness
• Coma

What should I do if I think I am infected with Baylisascaris?

You should discuss your concerns with your health care provider, who will examine you and ask you questions (for example, about your interactions with raccoons or other wild animals). Baylisascaris infection is difficult to diagnosis in humans. There are no widely available tests, so the diagnosis is often made by ruling out other diseases.

How is Baylisascaris infection treated?

A health care provider can discuss treatment options with you. No drug has been found to be completely effective against Baylisascaris infection in people. Albendazole has been recommended for some cases.

If I have Baylisascaris infection, should my family members be tested for the infection?

Baylisascaris infection is not contagious, so one person cannot give the infection to another. However, if your family may have been exposed the same way you were (such as contact with or exposure to an environment contaminated with raccoon or exotic pet feces), they should consult with a healthcare provider.

Raccoons are the primary, or definitive, host of Baylisascaris procyonis, a roundworm. Raccoons become infected with Baylisascaris in one of the following two ways:

• By eating infectious eggs during foraging, feeding, and grooming.
• By eating rodents, rabbits, and birds that are infected with the larvae of Baylisascaris.

Infected raccoons have been found throughout the United States, mainly in the Midwest, Northeast, Middle Atlantic, and West Coast.

Raccoons are peridomestic animals, which means they live in or around areas where people live. Roundworm eggs are passed in the feces of infected raccoons. Raccoons defecate in communal sites, called latrines. Raccoon latrines are often found at bases of trees, in unsealed attics, or on flat surfaces such as logs, tree stumps, rocks, decks, and rooftops. As more raccoons move into populated areas, the number and density of their latrines will increase.

The worms develop to maturity in the raccoon intestine, where they produce millions of eggs that are passed in the feces. Eggs that are excreted by raccoons are not immediately infectious. These eggs must develop in the environment for 2 to 4 weeks, after which the eggs are able to cause infection. The eggs are resistant to most environmental conditions and with adequate moisture, can survive for years.

While raccoons are the roundworm’s primary host, other types of animals can become infected. Birds and small mammals, such as rodents and rabbits, are susceptible to the parasite. Unlike raccoons, these animals sometimes show signs of infection, such as muscle spasms, tremors, and progressive weakness; infection can lead to death. Predator animals, including dogs, may become infected by eating an animal that has been infected with Baylisascaris. In some dogs, Baylisascaris may develop to adult worms and pass eggs in the dogs’ feces.

Young children are at risk for Baylisascaris infection as they may be more likely to put contaminated fingers, soil, or objects into their mouths.

People become infected by ingesting embryonated (fertile) eggs. Anyone who is exposed to environments where raccoons frequent is potentially at risk. Young children or developmentally disabled persons are at highest risk for infection as they may be more likely to put contaminated fingers, soil, or objects into their mouths.

Hunters, trappers, taxidermists, and wildlife handlers may also be at increased risk if they have contact with raccoons or raccoon habitats.

Fewer than 25 cases of Baylisascaris disease have been documented in the United States. However, it is possible that some cases are incorrectly diagnosed as other infections or go undiagnosed. Cases that are diagnosed tend to be severe.

Cases have been reported in California, Illinois, Louisiana, Massachusetts, Michigan, Minnesota, Missouri, New York, Oregon, Washington and Pennsylvania. As of 2018, there were 23 published human neurological cases in the US; six of the infected persons died.

People become infected when they accidentally ingest infective eggs in soil, water, or on objects that have been contaminated with raccoon feces. Baylisascaris infection is not spread from one person to another. When someone ingests these eggs, they hatch into larvae in the person’s intestine and travel throughout the body, affecting the organs and muscles.

Depending on where the larvae migrate, Baylisascaris infection can affect the brain and spinal cord (neural larva migrans), the eye (ocular larva migrans), and/or other organs (visceral larva migrans).

Signs and symptoms depend on how many eggs are ingested and where in the body the larvae migrate (travel). Ingesting a few eggs may cause few or no symptoms, while ingesting large numbers of eggs may lead to serious symptoms. Signs and symptoms of infection may take a week or so to develop and may include the following:

• Nausea
• Tiredness
• Liver enlargement
• Loss of coordination
• Lack of attention to people and surroundings
• Loss of muscle control
• Blindness
• Coma

If you suspect you have been infected with Baylisascaris parasites, consult your health care provider immediately. Be sure to tell your health care provider if you have recently been exposed to raccoons or their feces.

Diagnosis is difficult because symptoms depend on the number of infecting larvae and location in the body. Ocular larva migrans, when the larvae migrate to the eye, can cause sensitivity to light, inflammation of the eye, and blindness. Symptoms of visceral larva migrans, when the larvae travel to organs, depend on which organs are affected. For example, an invasion of the liver may cause hepatomegaly (inflammation and enlargement of the liver), while an invasion of the lung may cause pulmonary symptoms such as cough or chest pain. Larvae rarely end up in the nervous system but the most severe cases are neural larva migrans, when the larvae migrate into the brain and cause it to swell (encephalitis). There is no commercially available test for Baylisascaris infection. A health care provider may test blood, cerebrospinal fluid (CSF), and tissue to determine if an individual is infected. Eye examinations may reveal a migrating larva or lesions and are often the most significant clue to infection with Baylisascaris.

Diagnosis often is made by ruling out other infections that cause similar symptoms. Information on diagnosis and testing can be obtained through your local or state health department or CDC.

No drugs have been shown to be totally effective for the treatment of Baylisascaris infection. Albendazole, a broad spectrum anthelmintic, has been recommended for specific cases.

Early treatment might reduce serious damage caused by the infection. Should you suspect you may have ingested raccoon feces, seek immediate medical attention.

Baylisascaris infection can be prevented by avoiding contact with raccoons and their feces. Washing your hands after working or playing outdoors is good practice for preventing a number of diseases.

Do not keep, feed, or adopt wild animals, including raccoons, as pets. Infection rarely causes symptoms in raccoons, so you cannot tell if a raccoon is infected by observing its behavior. Roundworm eggs passed in the feces of infected raccoons are not visible to the naked eye. Eggs can only be seen using a microscope.

You may discourage raccoons from living in and around your home or parks by taking the following steps:

• Prevent access to food
• Keep trash containers tightly closed
• Close off access to attics and basements
• Keep sandboxes covered when not in use (raccoons may use sandboxes as a latrine)
• Remove fish ponds — they eat the fish and drink the water
• Eliminate water sources
• Remove bird feeders
• Clear brush so raccoons are not likely to make a den on your property

Stay away from areas and materials that might be contaminated by raccoon feces. Raccoons typically defecate at the base of or in raised forks of trees, or on raised horizontal surfaces such as fallen logs, stumps, or large rocks. Raccoon feces can also be found on woodpiles, decks, rooftops, and in attics, garages, and haylofts. Feces usually are dark and tubular, have a pungent odor (usually worse than dog or cat feces), and often contain undigested seeds or other food items.

If you have found a raccoon latrine near your home, cleaning the area may prevent possible infection. Newly deposited eggs take at least 2-4 weeks to become infective. Prompt removal and destruction of raccoon feces will reduce risk for exposure and possible infection.

If you choose to clean the site yourself, care should be taken to avoid contaminating hands and clothes.

• Wear disposable gloves to help prevent cross contamination.
• Wear a N95-rated respirator if working in a confined space to prevent accidental ingestion of eggs or other harmful materials.
• Avoid stirring up dust and debris- you can lightly mist the latrine area with water from a spray bottle to reduce the amount of dust.
• Wear rubber boots that can be scrubbed or cover your shoes with disposable booties that can be thrown away, so that you do not bring eggs into your household.
• Feces and material contaminated with raccoon feces should be removed and burned, buried, or sent to a landfill.
• Most chemicals do not kill roundworm eggs; however, heat kills the eggs instantly.
• Treat feces-soiled decks, patios, and other surfaces with boiling water or a propane torch (please contact your local fire department for regulations and safety practices).

To help further reduce the risk of possible infection, wash your hands well with soap and warm running water. Clean/launder your clothes thoroughly with hot water and detergent.

If you are cleaning an indoor raccoon latrine and are not able to use a propane torch, use a damp (but not wet) sponge to wipe the area with hot soapy water. Rinse your sponge frequently. After you are finished, flush dirty water down the toilet. Place the sponge in a plastic bag and put the plastic bag in the garbage.

Contact your local animal control office for additional assistance.

Dogs

Dogs may be infected with adult B. procyonis roundworms but may not show symptoms. Have all pets de-wormed under a veterinarian’s supervision and take precautions to avoid contact with their feces.

Exotic pets

Raccoons and dogs are not the only hosts of Baylisascaris. B. procyonis infection has also been documented in kinkajous. Other animals such as coatis may be susceptible. When wild animals are kept as pets, there can be a risk of disease transmission to humans.