Why is there a larger amount of diseases that humans are susceptible to than previous centuries?

Answer 1

I'm not positive if this is true! We may just have the technology to better differentiate and speciate diseases nowadays. For example, in our earlier history all "fevers" may have been thought to be caused by the same thing. Whereas now, we know of many febrile illnesses that range from influenza, to yellow fever, to ebola, to measles and beyond.