Toxoplasma gondii is an obligate intracellular protozoan parasite that infects a wide range of warm-blooded animals, including humans, and causes the disease toxoplasmosis. The parasite infects all members of the Felidae family (cats), as well as many other mammals, birds, reptiles and amphibians. In cats, the parasite is responsible for causing feline infectious peritonitis (FIP), a fatal disease. T. gondii has a complex two-host life cycle involving sexual reproduction in felids and asexual reproduction in all other hosts. Ingestion of infected meat or contact with contaminated cat feces can lead to infection in humans and other animals.
The first record of toxoplasmosis dates back to the early 1900s, when scientists observed strange behavior in laboratory rats inoculated with tissue from rabbits infected with T. gondii cysts. The rats lost their fear of cats, which led researchers to believe that the parasites were somehow manipulating their host’s behavior. Subsequent studies have shown that T. gondii can indeed change the way its host behaves; for example, it has been shown to increase mouse anxiety and make them more attracted to the smell of cat urine.
Toxoplasma gondii is thought to infect up to one third of the world’s human population; however, most people who are infected do not experience any symptoms because their immune system keeps the parasites in check. In people with weakened immune systems, however, such as those suffering from AIDS or cancer, toxoplasmosis can be deadly if not treated promptly with antibiotics. Pregnant women are also at risk; if they contract toxoplasmosis during pregnancy, it can lead to serious birth defects or even miscarriage.
There is no vaccine against toxoplasmosis and no cure once you are infected; therefore, prevention is key. If you must handle raw meat (particularly pork or lamb), be sure to wash your hands thoroughly afterwards and cook meat thoroughly before eating it (pork should be cooked until it reaches an internal temperature of 160°F). If you have a cat, have someone else clean out its litter box – Toxoplasma gondii oocysts can remain infectious in soil or sand for over a year!