Toxoplasmosis is a pretty awesome parasite if you have to pick a favorite. It has the ability to alter the behavior of its host to maximize its chances for reproduction. An infected mouse will lose its inhibition that normally causes it to fear the scent of predators, which increases the chance that it will be someones supper. Toxoplasmosis will then continue its life cycle inside a cat, where its warm and fuzzy.
Its estimated that one third of the worlds population is infected with toxoplasmosis, but its important to note that 80 to 90 percent of primary infections are asymptomatic. Most carriers of the disease (typically ladies ages 15-44) will never even know they have it! Toxoplasmosis is very dangerous if you are pregnant or immunosuppressed, so get tested by your doctor if you are at risk. (Kitties with FIV or feline leukemia are also at risk.)
You are more likely to contract the disease through unwashed produce and poorly cooked meat than via cat feces. Even though it makes your cats love you, try to refrain from feeding them raw meat. Use common sense when handling their litter boxes. If you have children, be mindful of public playgrounds. Stray cats love to bury treasure in the sandbox!
My good friend in med school told me that her professor advised students not to prescribe getting rid of the cat as a treatment for patients with toxoplasmosis. Most cases can be treated with folic acid or antibiotics. Those doctors are wicked smart.
SOURCES: Mayo Clinic, Centers for Disease Control, University of Oxford Press, Cornell University, UpToDate, AccessMedicine