Toxoplasma gondii (T. gondii), a one-celled parasite, causes toxoplasmosis in cats, humans and other animals. T. gondii has a high infection rate but generally produces only mild illness. Cats, both wild and domestic, are the primary hosts for T. gondii.
An infected cat sheds oocysts in its feces. A host accidentally ingests the eggs via some type of exposure to the feces. Once inside the host, the oocysts mature into the parasite. In intermediate hosts, such as humans and dogs, the parasite causes cysts but can't reproduce. Only a cat's gastrointestinal tract offers the perfect conditions to allow the parasite to mature and reproduce. That cat sheds new eggs, allowing the cycle to continue. Cysts that form in all hosts remain for life unless surgically removed.
Toxoplasmosis rarely produces symptoms in healthy hosts. Cats with compromised immune systems sometimes display lethargy, lack of appetite and fevers. Depending on the location of the parasite, the cat can be vulnerable to pneumonia, neurological impairment, blindness, lack of control over bodily functions, seizures and death. Blood work and patient history assist the veterinarian in diagnosing toxoplasmosis.
Treatment usually works if the cat is diagnosed before neurological impairment or other serious effects take hold. The cat starts and continues an antibiotic, usually Clindamycin, for several days after the last symptoms have disappeared. As of July 2009, there is no vaccine for toxoplasmosis.
Infection in Humans
Most humans aren't likely to catch toxoplasmosis from their cats, but immunocompromised individuals and pregnant women are at special risk. Those with immune system deficiencies aren't as able to withstand the side effects. While most pregnant women won't show signs of infection, their infants are at risk. It's uncommon for infants to be born with symptoms, so T. gondii remains undetected oftentimes for years. When symptoms appear, they are severe, from mental retardation to blindness and even death. Pregnant women should avoid cat litter or use gloves and a mask when changing the litter box to avoid infection.