Natural history of disease

• The term natural history of disease signifies the way in which a disease evolves over time from the earliest stage of its prepathogenesis phase to its termination as recovery, disability or death, in absence of treatment of presentation.
• Each disease has its own its own unique natural history which is not necessarily the same in all individuals . However the natural history of disease comprises two phases-

1. prepathogenesis phase: This is the period preliminary to the onset of disease in man. Agent, host and environment-this three factors interact during this phase and disease occurs.
2. pathogenesis phase: It begins with the entry of the disease agent in the human host. Usually there may be incubation period between the entry of the disease agent and onset of clinical sign and symptoms.