Found this on technovelgy.com, "where science meets fiction":
Toxoplasma Parasite Mind Control
Half of the world's human population is infected with Toxoplasma. Parasites in the body - and the brain. Remember that.
Toxoplasma gondii is a common parasite found in the guts of cats; it sheds eggs that are picked up by rats and other animals that are eaten by cats. Toxoplasma forms cysts in the bodies of the intermediate rat hosts, including the brain. Since cats don't want to eat dead, decaying prey, Toxoplasma takes the evolutionarily sound course of being a "good" parasite, leaving the rats perfectly healthy. Or are they?
here's the rest, here