A number of communicable diseases can constitute significant threats at local, regional or global levels leading to epidemics or pandemics.
Epidemic refers to an increase, often sudden, in the number of cases of a disease above what is normally expected in that population in that area. Examples of major epidemics include cholera, measles, malaria, and dengue fever.
Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people. Examples are Black Death, Spanish influenza, Asian influenza, Hong Kong influenza, and Coronavirus (COVID-19).