Should your cat's "No. 2" be considered a No. 1 health problem? Thanks to a hardy parasite that makes its home in cat feces, a growing number of animal disease experts are calling for a national health campaign to clean up after America's beloved felines.
"Nobody wants to talk about it, but our cats are outside pooping all over the place," said Patricia Conrad, a professor of parasitology at UC Davis' School of Veterinary Medicine. "There's a lot more out there in the environment than any of us would like to think about."
In a study published Tuesday in the journal Trends in Parasitology, two Maryland researchers calculated that both household and feral cats produce 1.2 million metric tons of cat feces each year -- a weight roughly equivalent to 12 aircraft carriers.
Although much of that dung has been discreetly covered by sand, garden soil or kitty litter, a small portion contains a dormant parasite called Toxoplasma gondii, which can infect humans and other warm-blooded animals.
It has long been known that infection by feces-borne parasites, or oocysts, can cause serious birth defects, including deafness and mental retardation. However, more recent and controversial studies have linked infection to increased risk of schizophrenia, suicidal behavior and brain cancer.
"There's increased awareness now that Toxoplasma gondii is a very clever parasite, and does strange things to the brain," said Dr. E. Fuller Torrey, lead author and director of the Stanley Medical Institute. "That's prompted us to re-evaluate it. It may be capable of doing more than we thought."
Torrey and study co-author, Dr. Robert Yolken, a neurovirologist at Johns Hopkins Medical Center, write that "accumulating T. gondii oocysts in the environment pose a significant public health hazard, especially in the sandboxes of children, gardens and other places favored by cats for defecation."
The authors are urging cat owners to keep their pets indoors and to properly dispose of cat litter. (Do not dump it outside or flush it down the toilet. Instead, bag it and send it to a sanitary landfill with the rest of your trash.)
They are also calling for a public health campaign to reduce the population of feral cats, and to educate members of the public on how to protect themselves from infection.
"It should be assumed that the play areas of children, especially sandboxes, are highly infectious unless they have been covered at all times when not in use, or ... are not accessible to cats," the authors wrote. "It should also be assumed that gardens to which cats have access are infectious, and gardeners should wear gloves and wash their hands after completing gardening.... Fruits and vegetables should be thoroughly washed."
Humans are usually infected when they eat the uncooked meat of an infected animal, or when they swallow or inhale oocysts directly. This can occur if drinking water is contaminated with infected feces, or if the waste matter becomes dry and dusty and is inhaled.
Authors note too that the parasite is extremely hardy, and can survive for years in freshwater and saltwater.
Epidemiologists in the United States began studying the potential health threats of cat feces after parasitic outbreaks in Canada, South America and Asia. In each case, drinking water was the source of the infection.
Conrad, of UC Davis, was not involved in the paper published Tuesday. However she did coauthor a study that linked an outbreak of disease among sea otters off the coast of California to runoff water that was contaminated with cat feces.
Conrad said she agreed with Fuller and Yolken, but said that the problem was chiefly one of feral cats, and house cats that spent time outdoors. Cats that never ventured outside were very unlikely to spread the parasite.
"The big polarizing question here is about feral cat control," Conrad said. "There are feral cat enthusiasts who are very sensitive to any discussion about it."
Conrad said public health and animal control officials should look for ways to reduce the feral cat population that do not involve euthanasia."We need to have a reasonable discussion about how effective are spay and neuter release campaigns, how effective are sheltering and fostering cats and what other things we can do to manage feral cat populations," she said. "Otherwise, its just uncontrolled growth.”
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