Interesting premise. Cats do carry Toxoplasmosis, which is also carried by rodents, but it needs to infect cats to reproduce. Current research suggests that in order to get from the rodent to the cat, toxoplasmosis re-wires (so to speak) the rodent's brain so that it stops fearing cats, and instead become attracted to the scent markers cats leave behind, making them easier prey. Sounds like the author knew about this and did a twisty 'what if?'.