(HealthDay News) -- As summer hits its stride, many Americans are taking a moment to step into their backyards and smell the roses. And lilies. And, uh, raccoon feces?
That's the case for many Americans living near woods or marshes. And backyard "raccoon latrines" -- spots created by the animal as a kind of shared public bathroom -- are ground zero for the transmission of a dangerous parasite called Baylisascaris procyonis, researchers say.
Raccoons infected with the intestinal roundworm tend to shed about 20,000 of the parasite's egg for every gram they leave behind in droppings, the researchers noted. Human infection, which can lead to the onset of encephalitis, can occur when children's muddied hands touch their mouth after inadvertently playing in an infected backyard.
"Contact with any fecal material, period, is a health risk, but raccoons carry a parasite which goes to the brain more often than other parasites and has devastating effects," explained the study's lead author, L. Kristen Page, an associate professor of ecology in the biology department at Wheaton College in Illinois.
"It's true that this might not seem like a big problem because there have only been a few cases documented so far," Page acknowledged. "But when this parasite does strike it almost always results in brain damage, or deafness or blindness or profound disability. So we'd like to help prevent that by alerting the public as to the easy steps people can take to protect themselves and their kids."
Eliminating tempting food sources, such as garbage cans and bird feeders, is one way to reduce the chance that raccoons will set up shop in the backyard, Page noted. Letting a house pet roam the backyard from time to time can also serve as a deterrent, she said.
A report on the infectious disease risk associated with raccoons appears in the September issue of Emerging Infectious Diseases.
Infected raccoons are "fairly common" across the United States, according to the U.S. Centers for Disease Control and Prevention, although most raccoons show no symptoms.
Human infections, though, are rare, the CDC reports. Less than 25 cases, including five that were fatal, have been reported since 2003, though the agency adds that additional cases might have gone undetected because the infection is difficult to diagnose.
Once ingested, symptoms take a week or more to develop as eggs turn into larvae and migrate through various organs, such as the liver, brain and spinal cord. Symptoms include nausea, fatigue, loss of balance or muscle control, liver enlargement and visual impairment.
For their study, the researchers surveyed 119 suburban Chicago backyards for evidence of raccoon latrines. All the backyards were located near a forest or marshland.
They found that about half the inspected yards had raccoon latrines, sometimes more than one, and about a quarter of those contained parasitic eggs.
Yards closest to a forest or marsh were most affected, the researchers found. The presence of pet food, bird feed or garbage outdoors made the latrines more likely, they reported, whereas outdoor pets had the opposite effect.
"Anywhere where you have high densities of people and raccoons, your children can be at risk," Page said. "Generally, the problem is more prevalent in areas that are not super hot because we know that heat kills the parasite eggs."
Anyone who finds raccoon droppings in their yard should clean the area immediately, she said. "Parasite eggs in fresh feces are not infective," she said. "It takes 30 days for them to become infective. You want to wear gloves and be careful, and if you're not sure how old the pile is, you need to be especially careful. But the risk is much, much less if you're picking it up fresh. And then I would also pour boiling water on the spot where you picked up the feces because that will kill the remaining eggs."
Dr. Philip M. Tierno Jr., director of clinical microbiology and immunology at New York University Langone Medical Center and a professor of microbiology and pathology at the NYU School of Medicine in New York City, said that such measures are worth noting, even if infection rate "is not a major problem."
"When it occurs, infection can be very dangerous," Tierno said, "So if you have any sign, you should go to your health-care provider and get tests run."
As for the issue of raccoons in the backyard, he said it's important to remember that they're wild animals.
"You shouldn't be in contact with them, or feed them or leave out garbage or food that will attract them," Tierno said. "And when you see or smell one of their latrines -- and it's like, wow! So you will certainly smell it -- take steps to remove it carefully but quickly."
The U.S. Centers for Disease Control and Prevention has more on raccoons and infectious disease.
By Alan Mozes
SOURCES: L. Kristen Page, Ph.D., associate professor, ecology, Department of Biology, Wheaton College, Wheaton, Ill.; Philip M. Tierno Jr., M.D., Ph.D., director, Department of Clinical Microbiology and Immunology, New York University Langone Medical Center, and clinical professor, microbiology and pathology, NYU School of Medicine, New York City; September 2009; Emerging Infectious Diseases
Last Updated: Aug. 14, 2009
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