Rats are smart.
They can tell Japanese and Dutch apart.
They figure out what the researchers are doing, steal some new anti-malarial drugs effective against toxoplasmosis and quickly deploy a global treatment scheme that is both cost effective and universal. The cats remain clueless and infected. Cat oocysts remain untouched. The number of wild rats eaten by cats plummets. Cats get hungry and most outdoor cats return to being indoor cats. Cats and toxoplasmosis live together ever after.
The rats then move on to a cure for rat diabetes. But that’s another post.