Cats are responsible for 1.2 million metric tons of feces in the U.S. environment annually.  In addition to being disgusting, the excrement may actually be a public health hazard.  A recent study found that a parasite known as Toxoplasma gondii (T. gondii), which was already known to exist in some feline feces, is actually more widespread than originally believed.

Eggs of the parasite, known as oocysts, are dangerous.  A single oocyst has been known to cause an infection in humans.  The study, published in Trends in Parasitology, found that, within a single square foot of soil, there might be anywhere from three to 434 oocysts annually.  Oocysts infect humans when they are ingested, accidentally or through deliberate action.  Ingestion can occur when changing the litter box, gardening, playing in a sandbox, drinking contaminated water, or eating unwashed fruits and vegetable.

In the U.S., there are an estimated 82 million cats that are kept as pets.  An additional 25 to 60 million feral cats also exist in the U.S.  Studies have shown that, at any given time, approximately one percent of cats are infected with T. gondii.  Once oocysts of the parasite are deposited in soil, they can live for up to 18 months, particularly if they are deposited in moist soil.

The Centers for Disease Control and Prevention (CDC) describes further risks of being infected from T. gondii for those that eat undercooked, contaminated meat or have other food contaminated by hands or utensils that came into contact with the contaminated meat.  Symptoms can exist without a person ever becoming aware of the specific infection that they have.  Milder symptoms are flu-like, while more severe symptoms result in damage to the brain, eyes, or other organs.  Pregnant women and individuals with a compromised immune system are most at risk for infection.  A child in the womb can also be infected through the mother.

The CDC states that T. gondii infections are treatable, though it is possible to cause permanent damage.  To prevent or reduce the risk for infection, cat owners should change litter daily because the parasite does not become infectious until one to five days after being deposited by the cat.  Those that are at a high risk of infection should avoid changing litter if possible.  To address risk from food and drink, cats should not be fed raw meats, humans should thoroughly cook all meats to kill parasites, and unpasteurized milk should be avoided.  Finally, gardeners should wear gloves and sandboxes should be kept covered when not used.