It’s been known for some time that rats and other animals can detect illness in others of their species based on scent. Rats will actively avoid sick packmates shortly after they fall ill, when there are few visible symptoms. Most people might believe that humans don’t notice sick friends quite so quickly and certainly not based on their scent. But is that belief really true?
It’s easy to identify someone with an illness if they show physical symptoms such as fever, sneezing, or exhaustion. It’s another matter to notice that person has just contracted a disease.