Natural history of disease

Natural history of disease: • Natural history of a disease refers to the course of the disease over a period of time, unaffected by treatment. • It 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 the absent of treatment or prevention. • It is a necessary framework, to understand the pathogenetic chain of events for a particular disease and for the application of preventive measures. • It is customary to describe the natural history of disease as consisting of two phases: prepathogenesis(i.e. the process in the environment) and pathogenesis(i.e. the process in man) 1. Prepathgenesis phase: This refers to the period preliminary to the onset of disease in man. The disease agent has not yet entered man, but the factors which favour its interaction with the human host already exist in the environment. The mere presence of agent, host and favourable environmental factors in the prepathogenesis period is not sufficient to start the disease in man. What is required is an interaction of three factors to initiate the disease process in man. 2. Pathogenesis phase: • The pathogenesis phase begins with the entry of the disease agent in the susceptible human host. • The disease agent multiplies and induces tissue and physiological changes, the disease progresses through a period of incubation and later through early and late pathogenesis. The final outcome of the disease may be recovery, disability or death.