Raccoon Parasite Seen As Threat To Humans

sealPurdue News

August 8, 1983

Raccoon Parasite Seen As Threat To Humans

WEST LAFAYETE, Ind. – A roundworm transmitted by raccoons has been responsible for one human death and is a serious threat to cause more fatalities, a Purdue University scientist warns.

Dr. Kevin Kazakos notes that the parasite, Baylisascaris procyonis, "is a well-recognized cause of fatal central nervous system disease in animals and should also be considered dangerous to man.

"It is impossible to overestimate the risk people take if they keep pet raccoons around without having them wormed. Of more than 500 raccoons we studied, 70 percent contained Baylisascaris roundworms."

Kazakos says that while the raccoon roundworm is known to cause devastating brain and eye damage in such animals as squirrels, rabbits, mice and even monkeys, it only recently was linked to a similar affliction in humans.

An 18-month-old rural Pennsylvania boy who died of a severe central nervous system disorder last year was the first documented human victim of the raccoon parasite. Based on his work with Baylisascaris as a cause of disease in animals, Kazacos assisted scientists at the Armed Forces Institute of Pathology in Washington, D.C., in the identification of the roundworm as the cause of the child's death.

Kazacos observes that "few pathologists would be familiar with Baylisascaris larvae in human tissue."

He says eggs of the roundworms are carried in raccoon feces and and spread into the soil or onto the grass or other surfaces when the feces break up. Other animals or humans become infected "by accidentally ingesting the eggs, which contain infective larvae," the scientist explains.

He notes that a single raccoon defecation can contain several hundred thousand eggs, many of which can remain infective after several years on the ground.

Can other infected animals pass along the raccoon roundworm?

No, says Kazacos, because the larvae never reach adulthood in other animals and consequently can't produce the eggs that start the infection process. The larvae become adults only in raccoons' intestines.

The Purdue scientist comments that it's important the public know there is such a potentially dangerous parasite, but "it's also important not to blow it out of proportion, to sensationalize it.

"Just handling a raccoon isn't going to kill anyone. Only significant infection--ingestion of roundworm eggs from areas contaminated by raccoon feces--could be harmful."

Kazacos says the boy who died "apparently had plenty of contact with raccoon-contaminated areas. There were numerous wild raccoons in the area; the family had had one for a pet, and there was a family of raccoons living in the residence's chimney and defecating down into the firebox.

"Since children tend to place soil and other things into their mouths, they are especially vulnerable to infection."

Clinical signs caused by the roundworm larvae in animals are often misinterpreted as signs of rabies, Kazacos says. "Some of the animals sent to us as possibly rabid infrequently have rabies--woodchucks, rabbits and squirrels are examples--but they've been seen acting peculiar and may have bitten someone and the first thought is they're rabid. Many of these animals are found to have Baylisascaris larvae in their brain."

Since Kazacos' laboratory in the School of Veterinary medicine has become known in the last several years as the only one in the country concentrating on the raccoon roundworm, he has been called on to examine suspect animals' tissues from many parts of the country. While he has personally documented outbreaks and cases in the Midwest, he notes there have been other serious outbreaks and cases in Georgia, Illinois, Iowa, Alabama, Pennsylvania and New York. He knows of other major outbreaks at a German zoo and at the Dublin Zoological Gardens.

Kazacos says raccoons themselves do not develop the central nervous system disease caused by the roundworms, and several other animal species--among them pigs, sheep and skunks--also seem to be resistant. "But many other species, including primates, are highly susceptible," he points out.

Dogs, he adds, are apparently affected only by high concentrations of the roundworm larvae.

He observes that while the young Pennsylvania boy is the only recorded case of a fatality in humans, there may be other cases which have gone undiagnosed or been misdiagnosed as something else. He also knows of several cases of human eye disease which may have been due to the parasite; in one such case, he remarks, the person was known to have had pet raccoons.

"Various reports of large, unidentified roundworm larvae in human eyes could be raccoon roundworm infection and ophthalmologists need to be aware of this," he observes.

He says there really is no treatment for the condition. "The problem is, once the larvae cause enough damage to the brain to produce symptoms, it's probably too late to do much good. So it's especially important to be aware of the parasite and to take precautions. These would include having pet raccoons examined for the parasite by a veterinarian and wormed often, avoiding contaminated areas and decontaminating such areas by burning.

"Special care should be taken in regard to young children."

Kazacos says his lab is trying to develop a blood test "so we can look for antibodies in the blood of people who were exposed and have reacted to the parasite. Even if they have been infected by small numbers of larvae and are not showing any symptoms, a test might show they were indeed infected, giving us an idea of the extent of this infection in humans."

Purdue News Service: (765) 494-2096; purduenews@purdue.edu