cat outside Toxoplasmosis is a disease caused by a microscopic protozoal parasite called Toxoplasma gondii (T. gondii). Many warm-blooded animals including most pets, livestock, birds, and people can become infected with T. gondii, but cats (all cat species, not only domestic cats) are the definitive host for T. gondii. This means that they are the only animals that pass oocysts (pronounced "oh-oh-sists"), the environmentally resistant stage of the parasite, in their stool to infect other animal species, including people.

T. gondii infection in cats

Cats are most commonly infected with T. gondii when they prey on infected mice, birds and other small animals. For indoor-only cats, the most likely source of infection is uncooked meat scraps or raw meat. When initially infected with T. gondii, a cat can shed millions of oocysts in its stool each day for several days. After the initial shedding period, most cats will not continue to pass oocysts in their feces.

Signs of toxoplasmosis

Most infected adult cats appear healthy, with no visible signs of illness. However, some cats may develop pneumonia, liver damage and other health problems. Signs of illness in cats include lethargy, loss of appetite, coughing, difficulty breathing, diarrhea, jaundice, blindness, personality changes, eye problems and other neurologic problems. There is currently no vaccine available for T. gondii, but treatment can be effective if the disease is diagnosed early. A blood test for T. gondii antibodies can help in the diagnosis of toxoplasmosis in sick cats.

T. gondii infection in people

Although infection with the parasite is relatively common in people, actual disease is rare. People can be infected with Toxoplasma gondii by handling or consuming undercooked or raw meat (particularly pork); consuming raw, unpasteurized milk (including goat’s milk) and milk products; handling or consuming unwashed fruit or vegetables that may have been contaminated with soil containing infective oocysts; the consumption of raw oysters, clams or mussels; the ingestion of infectious oocysts from the environment; and transmission directly to an unborn child from the mother when she becomes infected with T. gondii during pregnancy. Pregnant women and immunocompromised people are at higher risk for toxoplasmosis.

It has been suggested that handling cats poses a risk of infection, but this activity is unlikely to pose a risk of T. gondii infection for humans. Since most healthy cats groom themselves frequently, and it takes a minimum of 24 hours before the oocysts in the feces are infectious, it is unlikely that feces would remain on their fur long enough for any oocysts to become infectious.


Common sense measures can prevent the spread of T. gondii:

  • wash your hands after working with soil or handling raw or undercooked meat, vegetables, or unpasteurized dairy products;
  • don’t consume raw milk or other unpasteurized dairy products;
  • wash fruits and vegetables;
  • boil water from ponds and streams when camping or hiking;
  • don’t taste meat before it’s fully cooked
  • cook meat to appropriate temperatures;
  • wash and disinfect cutting boards, knives, sinks, and counters immediately after cutting meats.
  • cover all outside sandboxes when not in use to prevent cats from using them as litter boxes.

Important points for cat owners

If you’re a cat owner, remember:

  • You are more likely to be infected with T. gondii from undercooked meat or the environment than from your cat, and take the precautions listed above to protect yourself. You should also keep your cat indoors -- don’t allow your cat(s) to hunt rodents and birds.
  • Avoid raw foods. Only feed your cats cooked meat or processed food.
  • Change the cat litter daily before T. gondii oocysts “ripen” and become infectious.
  • Dispose of used litter safely, preferably in a sealed plastic bag
  • If your cat has long hair on its rear end that tends to collect fecal material, or does not adequately groom itself, carefully trim the hair or have your cat professionally groomed to keep the area clean.
  • If you are pregnant or immunocompromised, follow these additional precautions:
  • If possible, do not handle stray cats or adopt new cats during your pregnancy or illness. If a new cat comes into your family during this time, have it thoroughly examined by a veterinarian immediately to ensure it is healthy and to address any health concerns you may have.
  • Take extra precautions (hand washing, etc.) to avoid contact with cat feces.
  • If you own a cat, avoid changing the litter box if possible (e.g., ask your spouse, roommate, etc. to change the litter box) or change it daily (to avoid contact with oocysts after they have had sufficient time to become infectious), use rubber gloves when doing so, and wash your hands thoroughly afterwards.

The content on this page is a condensed version of our brochure, Toxoplasmosis, available in English and Spanish.