The most likely thing that most people develop when that are sick is an imbalance in their body, and often their mind as well. The other consideration is that that the sickness can come from within the body or from an external source, outside the body.
a fever.
caves will most likely develop whare caves develop.
they are likely to develop at warm humid areas.
Winter
If someone was to come in contact with a virus or bacteria that makes them sick this can develop overnight during sleep.
no not likely
The guinea pig most likely will not get sick.
I think the people who lived in slum areas are likely to get sick because people lived in crowded ,unsanitary conditions.
Yes, you're far more likely to get sick if you aren't eating properly.
It depends how far you are from the person. If you are three feet away from the person, most likely you could get sick. However, if you are a couple yards away, most likely the cough won't get you sick.
Early cities were most likely to develop near water because this made it easy to find food and to have fresh water. They were also likely to develop near mining areas and places where jobs were prevalent.
Cancer