Toxoplasmosis (commonly called toxo) is a disease caused by a microscopic protozoan called Toxoplasma gondii. You may have heard about this infection because of the danger to newborn children if a woman becomes infected while pregnant. Another reason cat owners should be aware of toxo is that the cat is considered the "definitive host" of the toxoplasma organism, meaning it is the only animal that sheds infectious toxo in its feces. All mammals can become infected with toxo. Infection can occur in two ways. One is by ingesting toxo that has been shed in the feces of a cat. This can occur through contact with soil where cats have defecated or through direct contact with a cat or its fecal matter. This is a very uncommon occurrence. The much more common method of acquiring toxo is by eating meat or prey which contains toxo in the form of a tissue cyst. In cats and other predatory animals this occurs commonly when they eat uncooked prey. In people it occurs most commonly through eating raw or undercooked meat since beef, pork and lamb can all contain toxo. When any animal, including people and cats, become infected with toxoplasma it usually is an inapparent infection with no illness. This is because the body’s immune system puts up a defense that stops the spread of the toxo and walls off the organism into a tiny tissue cyst which remains dormant for years. These are the same tissue cysts which if eaten can cause infection. In people the situation is different if the person who becomes infected has a compromised immune system, such as a person with AIDS or a person on immune-suppressing drugs. In these cases, the spread of toxo may not be held in check and it can develop into an overwhelming and sometimes fatal infection which may affect many organs including the lungs, liver, eyes and brain. The situation is also different if the person who becomes infected is a pregnant woman. The woman will generally have no apparent illness, but the toxo organism can pass to the fetus and result in damage to the eyes or brain causing congenital disease. When mammals other than people become infected a similar thing happens. The vast majority never have illness but may carry tissues cysts of toxo for life. Only a few whose immune system fails to stop the toxo will become ill. This holds true for cats as well. A high percentage of cats have toxo cysts but are not ill, but we only occasionally diagnose toxoplasmosis in cats where it causes disease of the eye, lung, brain or other organs. Cats are unique in that they are the only animal which gets toxo in the intestine. This usually occurs the first time a cat ever ingests toxo. Three days to three weeks after becoming infected the cat begins to shed the toxo in its stool. This usually causes no illness in the cat and the shedding stops after one to two weeks. The toxo that is passed in the stool is not immediately infective. It takes two or more days before the toxo is infective, but it then remains infective in soil or sand for months. There are diagnostic tests which can be done on both the blood and the feces of cats to check for toxoplasma. If your cat is ill with a disease that might be toxo, your veterinarian will probably suggest the blood test for toxo to help determine if that is the cause. The use of the blood or the fecal test on a healthy cat Is controversial. The blood test looks for antibodies to toxo in the bloodstream. If present they indicate that the cat became infected sometime in the past. This doesn’t mean the cat is or will become ill from toxo. Nor does it mean the cat is shedding toxo in the stool since that period of shedding is only a brief period following the initial exposure. If the blood test indicates the cat has no exposure to toxo, that cat poses no danger to a person now, but if it is later exposed to toxo, it will then shed toxo in the stool. The test done on the cat’s feces is also not completely reliable. The toxo organism is sometimes hard to find under the microscope and since shedding only lasts a short while, it is very easy to miss on a single stool test. If a cat’s stool test is free of toxo when the owner becomes pregnant, that does not assure that it will remain free of toxo throughout her pregnancy. Due to the problems with interpreting these test results, each cat owner should discuss with their own veterinarian which, if any, tests they recommend. Considering what has been said about toxoplasma, here are some recommendations on how to minimize your cat’s exposure to toxo. Keep your cat indoors to preclude its access to rodents and birds and to areas where stray cats may have defecated. Never feed your cat raw or undercooked meat, or unpasteurized dairy products. It is likely that in the near future there will be a vaccine to protect cats against toxo and your veterinarian may recommend it. Here are some recommendations on reducing the risk of toxo for people: Eliminate raw or undercooked meat and unpasteurized dairy products from your diet. Remember, far more people get toxo this way than from cats. Pregnant woman and immuno-comprised individuals should avoid litter pan care altogether. Another family member should clean out the feces daily since it takes a few days for toxo to become infective. It is best to wear rubber gloves and the pan should be frequently cleaned and disinfected using scalding water. Cover children’s sand boxes since they are natural litter pans for stray cats. Wear rubber gloves when gardening in an area where cats may have defecated. Make it a practice to wash your hands after gardening or contact with cats and after handling uncooked meat and vegetables. Discuss with your veterinarian whether blood or fecal tests should be run on your cat. If you are contemplating pregnancy, discuss with your obstetrician whether to have a blood test done on yourself for toxo.