Sometimes cats are infected with a parasite called Toxoplasma gondii. In its simplest form, this infection in cats is a lot like the infection caused by coccidia. The cat becomes infected by swallowing cysts (“capsulelike sacs”) that are in soil or other substances containing the forms of the Toxoplasma gondii organisms that resist nature. Then, more adult stages of the parasite develop in the wall of the cat’s intestine and eventually produce more cysts that pollute the cat’s surroundings in its own feces.

Cats can also become infected by hunting.  If birds or mammals swallow the cysts passed in cat feces, stages of the organism multiply in their tissues and stay in their bodies for their whole lives. If cats eat these carriers (“hosts”), the same stages of the Toxoplasma gondii are also capable of infecting the cat.

For unknown reasons, possibly due to other infections or an inherited tendency, cats can also develop infections from the tissue stages of the parasite. Usually, the infections do not cause disease; but sometimes cats with these infections can have serious outcomes that result in general ill health and eye problems.

The greatest concern with toxoplasmosis is that cysts released into the surroundings can infect people. Toxoplasma gondii infection is a moderately frequent event in people. In the United States, approximately 10 percent to 20 percent of people have the organisms in their bodies in much the same way that birds and rodents do. These organisms do not usually cause disease in the infected human beings. 

There are two times, however, when the organisms can be dangerous to people. One is when the disease occurs in people because their immune (disease protection) system is somehow damaged by other diseases or weakened by the use of drugs given to control other medical conditions. In those situations people can become very ill due to the rapidly multiplying organisms in their bodies. 

The second dangerous situation occurs in women who are pregnant. A Toxoplasma gondii infection can have severe consequences for a developing baby if the mother is infected with toxoplasmosis for the first time during her pregnancy.  The disease in the growing baby and, later, the child can show up as severe generalized illness, as eye disease, or it may actually remain hidden.

How will toxoplasmosis affect my cat?

Cats that are infected with Toxoplasma gondii usually do not have any signs of infection, although they may sometimes have diarrhea or soft feces accompanying the intestinal phase of the disease. In cases where cats develop generalized toxoplasmosis, the infection may show as serious general disease that may be associated with damage to the intestinal wall, liver, lungs, or nervous tissue. Some cats develop eye lesions.

How do I prevent my cat from getting Toxoplasma gondii?

Toxoplasma gondii infections can be prevented by removing your cat’s feces regularly from where the cat goes to the bathroom (be sure to wear gloves or use a long-handled scoop to avoid touching the litter when doing this). Cats also need to be prevented from hunting because they can get this infection from eating small birds or animals infected with the tissue stages of the parasite.

Can humans be harmed by Toxoplasma gondii?

People can be infected with Toxoplasma gondii, and they can develop severe disease.  Individuals whose immune systems are weakened or who are undergoing immune system therapy for another condition and are concerned about toxoplasmosis should talk to both their physician and their veterinarian. Women concerned about the potential effects that Toxoplasma gondii might have on their developing baby and the safety of having a cat in their household during a pregnancy should discuss the situation with their obstetrician and their veterinarian.

• Toxoplasmosis can be transmitted to humans. It can have severe consequences for the child of a pregnant woman or for immune-compromised individual.
• Cats with toxoplasmosis may show no symptoms, or may have diarrhea or soft feces.
• Some cats develop a more severe form and can suffer serious bodily damage.
• Prevent toxoplasmosis by changing cat litter regularly (don't touch it) and keeping your cat from hunting.