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Toxoplasmosis is a disease caused by a parasite called Toxoplasma gondii. The life cycle of Toxoplasma gondii involves an intermediate and a definitive host. A cat will ingest infected raw meat (from a prey such as a rat, mouse or bird) and the parasite is released into the cat's digestive tract. The parasite multiplies in the small intestine (intraintestinal infection) and produce oocysts. These oocysts are then excreted in the cat's feces. Oocysts can survive in the environment for over a year.
During the intraintestinal infection cycle in the cat, some T. gondii organisms may penetrate deeply into the wall of the intestine and multiply as tachyzoites. These tachyzoites then spread out from the intestine to other parts of the cat's body, starting the extraintestinal infection cycle. Eventually, the cat's immune system will have them enter a dormant stage by forming cysts in muscles and brain. These cysts contain bradyzoites, or slowly multiplying organisms.
Most cats infected with Toxoplasma gondii will not show any symptoms. Disease may occur in cats with suppressed immune systems, including young kittens and cats with feline leukemia virus (FELV) or feline immunodeficiency virus (FIV). A sick cat may have fever, decreased appetite, lethargy, pneumonia, blindness, circling, head pressing, difficulty chewing and swallowing.
Toxoplasmosis is usually diagnosed based on the history, symptoms and laboratory tests. Sometimes the oocysts can be found in the feces, but this is not a reliable method of diagnosis because they look similar to other parasites.
Treatment of toxoplasmosis is based on an antibiotic called Clindamycin. Treatment must be started as soon as possible after diagnosis and continued for several days after signs have disappeared. There is no vaccine available at this time for toxoplasmosis.
Can I be infected?
Owning a cat does not mean you will be infected with the disease. You will not get infected by touching a cat or through bites and scratches. Indoor cats that do not hunt prey or are not fed raw meat are not likely to be infected with T. gondii. In the United States, people are more likely to become infected through eating raw meat than from handling cat feces.
There are two human groups at high risk for infection with Toxoplasma gondii; pregnant women and immunodeficient individuals. Women who are infected during pregnancy will not have any symptoms. The majority of infants do not show signs at birth either. However, later in life they may develop loss of vision and hearing, mental retardation, and death in severe cases. In immunocompromised people (cancer, organ transplant, AIDS, etc.) you may see enlargement of the lymph nodes, respiratory disease and heart disease.
Nydia Melissa Perez, DVM