In the case of toxoplasmosis, the organism that causes it is Toxoplasma gondii. This parasite is found everywhere that cats are found. Many mammals can be infected with toxoplasmosis, but only cats shed the organism in their stools, where they can be passed to other animals. Oddly enough, though, most humans are not infected because of exposure to Toxoplasma organisms in the soil, litterpan or other source of exposure cat stools. Most humans are infected by eating undercooked meat, especially pork and lamb.
Cats actually acquire the infection from eating raw prey most commonly, too.
Adult humans who become infected usually are unaware of the infection but may have flu-like symptoms. In humans with immune compromise, such as victims of AIDS, Toxoplasmosis is a much more severe infection, though. Toxoplasmosis can be very harmful if a pregnant women acquires the infection during a pregnancy. The infection must be new and it must occur during the pregnancy for problems to occur. If a woman has been previously exposed to toxoplasmosis and has antibodies against the organism, her immune system will protect her baby from infection.