UPDATE FEBRUARY 23, 2016: New research from Duke University reevaluates the information below. Read more here.
Toxoplasma gondii (T. gondi) is a common parasite; about 1-in-5 Americans are infected though many do not know it. It is a parasite commonly transmitted by eating undercooked and contaminated meat, drinking contaminated water, and coming into contact with an infected cat's feces. A healthy immune system is usually capable of handling the parasite, however, pregnant women, older people, and anyone with an immune system disorder are at greater risk. If one develops symptoms, they are flu-like and may include aching muscles and swollen lymph glands. Women who have been pregnant have likely been warned that the infection is dangerous and even fatal to a developing fetus.
Though the effects of the parasite on developing fetuses are well-known, new research suggests that T. gondii is associated with schizophrenia in the larger population that was formerly believed to show no adverse symptoms. "There is increasing evidence that infection with Toxoplasma gondii, a common parasite of people, cats, and rodents, is associated with an increased risk of a diagnosis of schizophrenia," writes Gary Smith, a professor of population biology and epidemiology at the University of Pennsylvania’s School of Veterinary Medicine. His recent study sought to rectify problems in former studies such as neglecting to factor in the increased risk of infection with T. gondii with age. Smith attempted to calculate how important of a factor T. gondii is in schizophrenia diagnoses and found that 21.4 percent (roughly one-fifth) of schizophrenia cases could be prevented if the parasite were not present.
So what does that mean for the public? Getting rid of your cat is not recommended as a method to safeguard you from the parasite. As mentioned before, what you eat may infect you. It is also unlikely that you would know you have the parasite as most people do not have symptoms. The new evidence is helpful, however, for medicine and research when attempting to address schizophrenia, which affects more than 3.5 million people. With understanding the parasites significant impact, there may be greater impetus for finding ways to prevent or reduce the number of infected people.
If you are at greater risk for having a severe infection by the virus (e.g., compromised immune system or pregnant) and own a cat, you may safely keep your lovable companion with a few precautions. The Center for Disease Control recommends:
Ensure the cat litter box is changed daily. The toxoplasma parasite does not become infectious until one to five days after it is shed in a cat's feces.
Avoid changing cat litter if possible. If no one else can perform the task, wear disposable gloves and wash your hands with soap and warm water afterwards.
Keep cats indoors.
Do not adopt or handle stray cats, especially kittens. Do not get a new cat while you are pregnant.
Feed cats only canned or dried commercial food or well-cooked table food, not raw or undercooked meats.
Keep your outdoor sandboxes covered.
Infected cats are only able to transmit the infection in their feces for a few weeks after they are infected. They too rarely show symptoms. Toxoplasma in your cat will go away on its own. Stay safe and be informed. Talk to your primary care veterinarian if you have any other questions.