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Raccoon Roundworm

What is raccoon roundworm?

Raccoon roundworm is a type of worm that infects raccoons and can cause serious disease in humans that accidentally come into contact with it. The adult worms live in the intestines of raccoons and deposit eggs which can contaminate soil around raccoon latrines. Humans, particularly children, can become infected by coming into contact with roundworm eggs from contaminated soil. The disease has little effect on raccoons but can cause severe, permanent brain damage in young children. For this reason, it is important to avoid contact with raccoons or areas they frequent. It is especially important to prevent raccoons from taking up residence in your yard, garage, or attic.

What does the District do about raccoon roundworm?

The District does not control raccoons, but does monitor for the presence of raccoon roundworm and distribute information to the public. If you believe you have a raccoon latrine on your property, we can provide an inspection and safe clean-up advice.

Does raccoon roundworm exist in San Mateo County?

Yes! In 2001, the District conducted a survey of local raccoons in conjunction with the San Mateo County Health Dept, Division of Environmental Health. Fifty-eight raccoons collected by private pest control operators from local residences were examined for worms. Almost three quarters of these (74%) carried raccoon roundworms in their intestines! Raccoons have become extremely common around homes in San Mateo County, even in highly urbanized areas such as Foster City and Redwood Shores, and many of these animals are infected. In 2005, a pet dog in Hillsborough became infected with raccoon roundworm larvae and died from severe nerve and brain damage. Raccoon feces containing roundworm eggs were found in the owner’s back yard.

What are the symptoms of raccoon roundworm?

  • In people: sudden lethargy, loss of balance, abdominal pain, paralysis of one or both sides of the body, loss of muscle coordination, head tilt, blindness, coma, and death
  • In raccoons: symptoms are rare
  • In squirrels, birds, and other small mammals: These animals serve as intermediate hosts to the worms and suffer the same symptoms that humans do. Typical symptoms include difficulty walking, loss of fear of people, circling, loss of balance, and paralysis.

How can I protect myself?

Raccoons live quite comfortably in residential neighborhoods throughout San Mateo County. They have adapted to the loss of their natural habitat by learning how to obtain food and shelter among our homes and businesses. Uncovered garbage cans, pet food left outside, and easy access to the crawl space under homes all provide an open invitation to encourage raccoons.

There is no effective treatment for raccoon roundworm, so it is very important to prevent raccoon roundworm infection.

The following steps can discourage raccoons from taking up residence in your yard.

A long recessed area surrounded on all sides by walls - some wooden and some metal. The bottom of the area is metal and is covered with raccoon feces.
Raccoons defecate in the same area. The area is called a raccoon latrine. Raccoon latrines may have a dangerous parasite and should be cleaned very carefully.

Raccoons often live comfortably in cities and suburbs. Sometimes considered pests, raccoons have adapted well to their decreasing natural habitat by adapting to humans, which provide raccoons with plenty of food and shelter. This often includes digging through garbage cans and entering houses in colder months. Without food or shelter, raccoons will go away and look for these essentials elsewhere.

  • Do not leave pet food out unattended in your yard
  • Keep garbage cans closed with a bungee cord or tie and empty them frequently
  • Cut tree limbs back from roof to prevent raccoons from entering the house
  • Prevent the accumulation of fruit on trees or on the ground beneath them
  • Seal the area under homes and out buildings to prevent raccoons from establishing dens there (if raccoons are already living under your building, contact the District or a private pest control operator for advice)
  • Seal off all outside openings to house attics

Additional steps you can take:

  • Do not keep raccoons as pets. Not only are they not suitable for pets because they are wild animals, but they may pose a serious health risk.
  • Learn to recognize raccoon latrine areas and either stay away from them or clean them up if necessary. Favorite spots are at the base of trees, in the forks of trees, on fallen logs, large rocks, woodpiles, decks, in attics, garages, chimneys, barns, and outbuildings. In addition, raccoons like to nest in hay lofts and may contaminate hay or straw that is used for bedding or food. Purchase hay or straw from a clean source and dispose of any bales that show evidence of fecal contamination. Do not store the hay you buy in areas that raccoons have access to. Be cautious using and handling fallen timber for firewood.
  • Teach children not to put soil or unwashed hands in their mouths

What is a raccoon latrine?

The split trunk of a very large tree. In the middle of the branches, there are large amounts of raccoon feces.
A raccoon latrine in the niche of a large tree.

A raccoon latrine is a site that many raccoons use to deposit feces. Raccoons tend to deposit their feces in specific spots. A site is often used by several different individuals over a long period of time. Latrines are often found on roofs, in attics, in tree crotches, on woodpiles or along fence lines or foundations of buildings. Latrines indicate that raccoons have taken up residence nearby or frequently visit an area in search of food. These sites can contain millions of roundworm eggs and are extremely dangerous.

What do I do if I find a raccoon latrine?

Keep children and pets away from the area and, if possible, clean it up. Clean up of raccoon latrines is difficult. The eggs of raccoon roundworms can survive for many years. They are resistant to all common disinfectants including bleach. The best way to kill the eggs is through flaming the area (including soil) with a blowtorch or burning affected material such as straw or wood cages. Alternately, boiling water can be poured over small areas at a time. In heavily contaminated areas, it may be necessary to remove and bury the soil in a deep spot elsewhere. When cleaning up any latrine area, proper protection is a must. This should include a dusk mask over the nose and mouth, disposable clothing, disposable gloves, and heavy rubber boots that can be cleaned with boiling water.

What is the life cycle of raccoon roundworms?

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Roundworm eggs are deposited and consumed by an intermediate host, such as mice, chipmunks, birds, etc. The eggs hatch into larvae which migrate into the liver and lungs of the intermediate host. Once in the lungs, the larvae can migrate further into other systems such as the eyes and central nervous system. Within a few weeks the larvae finish migration and encapsulate. If the dead animal is eaten by a raccoon, the capsule can open releasing eggs into the raccoon intestine where it is deposited in feces often in group latrines and the cycle begins again. You can learn more about the raccoon roundworm lifecycle on CDC's website HERE

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