Cats in the United States release about 2.6 billion pounds (1.2 million metric tons) of feces into the environment every year. Cat dung carries the parasite Toxoplasma gondii, a single-celled organism that creates infectious agents called oocysts. These oocysts can infect pregnant women, causing congenital problems in the baby such as deafness, seizures, eye damage and mental retardation. The parasite also infects people with compromised immune systems, such as those with HIV/AIDS.
After reviewing past studies on the parasite, a team of researchers believes the Toxoplasma parasite may be a significant public health problem, infecting people who are otherwise healthy. Other studies have even linked the parasite to schizophrenia, depression, suicidal behavior and lower school achievement in children.