What is an epidemic?
Infectious disease has always existed around both humans and animals. Ever since people began living in communities, disease could pass easily from one person to another. Often, only a few people become ill. When, however, the problem spreads outside a limited group, affecting a large number of people and lasting for some time, it is called an epidemic. If it becomes established right across the world, then it is a pandemic. Diseases that are present all of the time are said to be endemic – for example, malaria is endemic in certain tropical regions. Infectious disease is caused by microorganisms such as viruses invading the body. Also known as microbes, these microorganisms are carried in various ways, such as via animals or through the air.