Describe at least three ways that an infectious disease, like smallpox, can significantly impact history.

 Describe at least three ways that an infectious disease, like smallpox, can significantly impact history.   Why was variola virus such a dangerous pathogen?   How did developments in the prevention of smallpox help lead to our current practice of immunization? Why was smallpox a good candidate for eradication?  What were the challenges to eradication? 

250-300 words