What is a disease? And what is an infectious disease?

Disease is an abnormal medical condition that negatively affects a person and is accompanied by a distinguishing set of signs and symptoms. Disease in humans can result from injuries, unhealthy lifestyle choices, genetics, socio-economic circumstances, and the normal process of aging.

Other diseases are caused when a person comes in contact with microscopic organisms known as pathogens, such as viruses and bacteria. Diseases caused by pathogens are known as infectious diseases. An infection occurs when a pathogen begins growing within the person the pathogen has invaded.