Parasites in cat feces could be transmitted to humans, and could cause serious birth defects, including deafness and mental retardation, as well as an increased risk of schizophrenia, suicidal behavior and brain cancer. A new study urges cat owners to clean up after their pets.

"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."

A new study published Tuesday in the Trends in Parasitology journal calculated that both household and feral cats produce 1.2 million metric tons of cat feces each year, The Los Angeles Times reports.

Cats usually cover up their feces with sand, garden soil, or kitty litter, but some of the dung contains a parasite called Toxoplasma gondii, which can infect humans.

Humans can be infected if they swallow or inhale the parasite. The most common contraction of the infection is by drinking water contaminated with infected feces, or if the dung becomes dry and dusty and is inhaled.

According to CBS News, the parasite could cause birth defects, and an increased risk of schizophrenia, depression, suicidal behavior, as well as lower school achievement in children.

"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, wrote 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 urged cat owners to keep their pets indoors and properly dispose of cat litter by bagging it and putting it with the rest of your trash, instead of dumping it outside or flushing it down the toilet.

They also proposed a public health campaign to reduce the population of feral cats, and to educate the public on how to protect themselves from infection: gardeners should wear gloves, pregnant women should avoid changing kitty litter, and people should stay away from feral cats.

"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," the authors noted.