OUTBREAK: 10 OF THE WORST PANDEMICS IN HISTORY
Scientists and medical researchers have for years have differed over the exact definition of a pandemic (is it a pandemic, or an epidemic), but one thing everyone agrees on is that the word describes the widespread occurrence of disease, in excess of what might normally be expected in a geographical region.
Cholera, bubonic plague, smallpox, and influenza are some of the most brutal killers in human history. And outbreaks of these diseases across international borders, are properly defined as pandemic, especially smallpox, which throughout history, has killed between 300-500 million people in its 12,000-year existence.
A final note: The most recent outbreak of the Ebola virus, which has killed thousands of people, is still confined to West Africa. It may someday be pandemic, but for now, it is considered an epidemic — and is therefore not included on this list.