Starting in the early 1990s, he began to suspect that a single-celled parasite in the protozoan family was subtly manipulating his personality, causing him to behave in strange, often self-destructive ways. And if it was messing with his mind, he reasoned, it was probably doing the same to others.The parasite, which is excreted by cats in their feces, is called Toxoplasma gondii (T. gondii or Toxo for short) and is the microbe that causes toxoplasmosis — the reason pregnant women are told to avoid cats’ litter boxes.