via West Hunter
The background is that toxoplasmosis infects many warmblooded
creatures as the intermediate host, but can only sexually reproduce in
cats, their definitive host. These protozoans (apicomplexans, like
malaria) need to have their intermediate host eaten by a cat, and
they’ve apparently evolved methods of manipulating host behavior to help
bring that about, probably through their colonization of the brain.
There is some evidence that toxoplasma in the brain has effects on
human behavior, such as slowed reaction times, reduced long-term
concentration, and, of course, liking the smell of cat urine.
The changes in mice sure look like host manipulation, and I have
wondered if it might be happening in humans – in particular, cat ladies,
but maybe this played a role in the whole human domestication-of-cats
thing. Then again, perhaps it was toxoplasma domesticating humans. But
if this manipulation happens in chimpanzees, you just know it has to
work in humans. This suggests that if you eliminate the toxoplasma in
the brains of cat ladies, say with Atovaquone and Clindamycin, you could
perhaps cure their morbid attraction, just as antibiotics can cure
parthenogenesis in parasitic wasps infected by Wolbachia. Cured, they
might put all their flea-bitten parasites in a sack and throw them into
the river. And get a dog.
About half the human race has toxo on the brain, as if we didn’t already have enough trouble.
The big question (other than helping explain human craziness) is
whether this is an important part of how cats make a living. It may be
that toxo is an essential ingredient in cat predation strategies: if so,
it is probably very old, and may even go back before cats, perhaps
switching from some creodont.
If toxo naturally can make people like cat piss, it’s already
preadapted to become (with suitable genetic engineering) the model
system for many kinds of infectious behavior modifiers.