Toxoplasmosis has long been known to modify the behavior of its host mice, influencing them in ways which make it more likely they will be eaten by a cat. The microbe reproduces in the intestines of felines. The chemicals it produces to effect this appear to also have an impact in other mammals, including humans. As cats do not normally eat humans, effects on humans are just an accident.
Natural selection will eventually produce a toxoplasmosis microbe which forces humans to take felines into their homes and care for them, producing a much larger population of suitable environments for their reproduction. When this happens, when large numbers of humans willingly share their homes with cats, then we will know that the microbes have taken over.