It would be really interesting if in addition to infections, humans could contract diseases. I think it would also be a cool spin to add rodents to the game which can raid food stores and increase the likelihood of disease spreading. Some diseases could be deadlier than others - like the animal diseases are - and diseased humans could have lower productivity along with the usual health decline. Along those same thoughts, cats began entering human settlements once rodents began raiding food stores, so I think this could potentially be a neat side feature to explore. More food = More rats = More disease, and you need to maintain a cat population to help break the cycle and preserve food stores. Just a thought but it'd be cool to see that dynamic play out!