Forum Discussion
There's not much to study. Infected sims receive a moodlet (debuff) that tells you exactly how long they still have before they succumb and then they can order a cure at the computer ("Research Rodent Fever"). They leave a cool ghost, though. The pack lifestream should have some footage as has this video: https://www.youtube.com/watch?v=a-XOxxV4IwI
There should be a number of rodent fever ghosts in the gallery (I'd be surprised if there weren't), but with only basegame you won't be able to use them.
If you're interested in twists of infections in Sims games, look up the Strangerville expansion! It comes with a questline regarding a spores infection that will spread and can (but doesn't have to) stopped by the player. Quest-based gameplay of that kind is rare in Sims 4, in this form it occurs only in the Strangerville and Journey to Batuu packs.
I absolutely love the Strangerville infection! The whole pack definitely was a breath of fresh air -at least when it comes to gameplay- when it was released. I haven't played with the Rodent Fever that much, but I had my fair share of gameplay hours when Strangerville arrived and I also loved the CAS and Build/Buy Mode objects. The quest-based gameplay kind of reminded me of The Sims: Medieval, which is an installment I adore.