Diseases have ravaged human population for centuries bringing down kings and kingdoms. Thus, an Epidemic can be termed as a disease which effects a huge population.
In most of the cases an epidemic is restricted to only one location, but sometimes it might spread to other places, countries or continents which in turn affects millions of people.
An outbreak is used as a synonym for an epidemic. In America there are numerous outbreaks which are responsible for major life loss.
The most dangerous infection introduced to Americans by Europeans is the small pox which has been responsible for huge loss in life of the Natives. Spanish Influenza stands in second place with spread of infection globally while Typhoid stands in third position.
Malaria is another deadly infection which is caused by mosquitoes and has led to huge loss of life . Other diseases which terrified American population are Polio, Tuberculosis and HIV.