I've suspected for a long time that yes, humans get infected and it changes mental processes. Not just toxoplasma either - for example, one can get infected by one-celled yeasts that convert carbohydrates into low levels of alcohol within your body. I've been hit with this and when it happens one feels fuzzy and a little floaty. Cutting all sugar from diet and taking anti microbials eventually cures it.

But toxoplasma goes to the brain, and I've always thought that many, many cat-lovers get it from their animals, and it messes them up. No longer able to be coldly rational people but now emotionally driven more than normal.

People also get intestinal worms. In Southern California, ERs see cases of people coming in with seizures. Diagnostics reveal they have worms in the brain, from eating improperly cooked pork. Which is why I never ever eat off a Mexican food truck. I'll eat Mexican if it's been nuked.

Historically, there has been another aspect. In past centuries, people too often ate bread made with rye flour infected by ergot fungus. The fungus produces an LSD-like chemical. People then hallucinated. Some religious fervor no doubt came from things like that.

It's easy to predicate demons when many biologic causes can have the same effect.