Rare Raccoon Parasite Causing Blindness & Severe Brain Damage Could Be More Widespread Than We Knew

So cute, so furry, and so chock full of parasites. While raccoons are fun to watch, they are neither friendly nor clean — and they can make you sick in more ways than one.

Native to North America, you can find raccoons just about everywhere except for parts of the Rocky Mountains and southwestern states. Raccoons are naturally adaptive and have successfully managed the transition from woodland and streamside environments to suburban neighborhoods, parks, and urban areas. Quick to take up residence in buildings, eaves, and crawl spaces, it is not unusual for a raccoon to exploit structural holes in dwellings to make itself at home.

Alone or with a young family, raccoons can create formidable obstacles. They are intelligent, persistent, and exceptionally destructive. If you or neighbors are feeding or providing backyard support for raccoons, it will eventually be a problem if it is not already. As territorial animals, it does not take a lot to cause a raccoon to bite or scratch, even if raised as a family pet. Raccoons are mid-size mammals that can damage your house, property — and your health.

Raccoons — Not Good for Your Health

In addition to being aggressive, raccoons can carry dangerous disease and parasites. In a recent study published in the Center for Disease Control and Prevention journal, Emerging Infectious Diseases, researchers from the University of California explored rates of infection of California residents with Baylisascaris procyonis, the "raccoon roundworm."

B. procyonis is a roundworm that lives its full life cycle in raccoons. They're pretty common, too: 70-90% of raccoons have them. Humans and dogs can serve as hosts as well. Raccoons shed the eggs of these parasites in areas where they live and frequent. Birds and mammals ingest the roundworm eggs too. Internally, the eggs hatch in the host and the larvae move to the gut wall and tunnel into body tissues where they form a protective cyst around themselves. The cycle is complete when the adult roundworms lay eggs in the small intestine, which humans and dogs deposit into the environment in feces.

While humans are not a primary target of roundworms, children who play in areas where raccoons are present ingest their parasites when they put their hands in their mouths after playing outside. In humans, B. procyonis continues to grow, causing physical damage as it migrates through the body. The parasites can cause fatal neurological symptoms and blindness, although, the grimly good news is that less than 5% of these roundworms infiltrate the brain — only about 25 cases have been documented in the US, according to the CDC.

Baylisascaris procyonis larva in tissue section of brain

This illustration depicts the life cycle of Baylisascaris procyonis.

Baylisascaris procyonis larva in tissue section of brain

This illustration depicts the life cycle of Baylisascaris procyonis.

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In addition to roundworms, raccoons carry leptospirosis, a bacterial infection carried in the urine of infected wild and domestic animals like rats, raccoons, or dogs. Humans and their pets become infected when they come in contact with water or soil where raccoons or other wildlife have urinated. Often asymptomatic, leptospirosis can also cause liver failure, respiratory trouble, meningitis, or death.

The most frequently reported mammal with rabies in the US is the raccoon. In June, a jogger in Maine drowned a rabid raccoon, even as it chewed up her hand. In July, a raccoon in Hampton, Virginia tested positive for rabies.

Testing for Infection

The report notes that "infection is not frequently reported," and researchers in the California study initially state B. procyonis is rare. Their study findings suggest otherwise. Between 2014 and 2016, the study team offered free roundworm testing and education about raccoon roundworm to adults, ages 18–75, who lived in the area of Santa Barbara County for more than three years.

Through this outreach, researchers were able to test 150 volunteers, including 12 individuals who worked with wildlife or animal rehabilitation. After collecting, storing, and processing the blood samples from volunteers, and comparing the results to questionnaires filled out by participants, the team made these findings:

• None of the 12 researchers and wildlife rehabilitators tested positive for B. procyonis antibodies.
• Among the volunteer participants, 11 tested positive for antibodies and reported they had seen raccoons in their neighborhood during the past year. Seven of these had seen a raccoon in their yard in the previous month.
• Of the 11 individuals who tested positive for antibodies to the parasite, nine noted they had no contact with raccoons or their feces. The other two reported exposure between two and 12 months before testing.
• Those who tested positive included an administrator, social worker, zoo volunteer, retiree, researcher, and engineer. Some of them had dogs, fed wildlife, gardened, or had sandboxes.

Study authors believe their sample size was skewed by demographic data because their recruiting efforts targeted individuals interested in outdoor activities. Overall, the sample size that tested positive led researchers to believe that more people than estimated suffer asymptomatic infection with B. procyonis. Anyone living in areas where raccoons reside are at risk of infection — prevention is important.

Taking Steps to Avoid Raccoons

Even if raccoons live in your neighborhood, you should discourage their presence on your property, and avoid them when you are on theirs. When there are raccoons around, it is important to avoid the community areas they use as bathrooms. Called "raccoon latrines," you can find these infection dumps in trees, on raised flat surfaces like wood piles, balconies or decks, attics, sheds, or garages.

Raccoon roundworms are easily transmitted but tough to kill. Cleaning is not enough, not even with alcohol, bleach, or soap — and the chances are good you will become infected if you try to clean up a raccoon den by yourself. The eggs can survive more than a year laying in wait, or in your pool if a raccoon decides to wash there. Chlorine does not kill Baylisascaris eggs. If you have a raccoon problem, getting professional help is a good idea to avoid being infected or spreading contamination. If you go it alone, you will need appropriate personal protective equipment.

Tips for steering clear of raccoons include:

• Cover your pool, keep the gate around your pool closed (although raccoons can climb).
• Do not feed raccoons, ask anyone in your neighborhood who you know is partial to raccoons to stop. Do not leave pet food outside, and encourage others not to as well.
• Keep your house in good repair and watch for signs of rodent or raccoon damage or entry.
• If you compost, do not add meat, grease, or dairy products to the pile, and ensure you have a tight-fitting lid.
• Do not leave uncovered trash out, and encourage others to use appropriate lidded cans as well.
• Vaccinate pets appropriately, especially for rabies.
• Wear gloves when gardening — always.

"If you see a raccoon in Santa Barbara, the chances are that it's full of roundworms," study researcher Sara Weinstein said a press release. "That is true in varying degrees throughout North America, where urban raccoons may infect people more than previously assumed."

Inside and out, raccoons are wildlife. Keep yourself, family, and friends healthy by keeping your head up for — and hands away from — these cute, but dangerous furry mammals.

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Cover image via D. Gordon E. Robertson/Wikimedia