There are a few parasites which are known to affect the higher functions of the mind - rabies making dogs vicious, parasitic wasps which commandeer orb spiders, flatworms which make ants commit a strange sort of suicide atop blades of grass, where they can be eaten by sheep. And, of course, there's toxoplasma gondii, whose primary habitat is in the intestines of cats, and which can be responsible for "crazy cat lady syndrome."

There are a few parasites which are known to affect the higher functions of the mind - rabies making dogs vicious, parasitic wasps which commandeer orb spiders, flatworms which make ants commit a strange sort of suicide atop blades of grass, where they can be eaten by sheep. And, of course, there's toxoplasma gondii, whose primary habitat is in the intestines of cats, and which can be responsible for "crazy cat lady syndrome."

But while we usually think of this as being a rare, acute condition affecting only a few people, it turns out that infection rates may be far higher than we imagined - 10-20% of Americans, and over 50% of Europeans - and that even these low-level infections may have subtle but significant effects on our personalities.

We may well be, in short, under the effect of mind-controlling parasites right now. And things as fundamental as our introversion or extroversion, or as seemingly arbitrary as our fashion sense, may be affected.

Via A.V. Flox​
https://www.theatlantic.com/magazine/archive/2012/03/how-your-cat-is-making-you-crazy/308873/