Toxoplasma gondii
I keep up with research on schizophrenia because my brother Steve has it. (Hence reading Deleuze and Guattari is always a little strange for me, shall we say.)
One theory floating around right now is that a neurotoxin released by toxoplasmosis gives rise to symptoms of schizophrenia and possibly Alzheimer's.
Toxoplasmosis is caused by a protozoan symbiont that lives in most people's brains harmlessly. Cats are common hosts and cat poop contains a lot of the protozoans. One theory is that cat poop near to pregnant humans is a way for the symbiont to jump. One in five of us humans carry the symbiont.
So when schizophrenic people tell you that aliens have invaded their head and that they need surgery, their paranoia is telling the truth. My brother would talk about aliens and also demand brain surgery “because a piece of my brain has come loose.”
Melancholy coexistence...