Natural history and progress of disease Mr. Manish Chaudhary MPH, BPKIHS

Natural history of disease The word natural history of disease is the key concept in epidemiology. It signifies the way in which a disease evolves over time from the earliest stage of its pre- pathogenesis phase to its termination as its recovery, disability or death, in the absence of treatment or prevention.

Natural history of disease Susceptible host TIME Incubation period Death Recovery Exposure Onset Latent Infectious Non-infectious Infection No infection Clinical disease

Natural history of disease consist of two phases- –Pre-pathogenesis phase (i.e. the process in environment) –Pathogenesis phase (i.e. the process in man)

PHASES PHASES Prepathogenesis Pathogenesis

Pre-pathogenesis phase the process in environment the process in environment 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 the onset are already existing in the environment.

Causative factors of disease Three factors referred as epidemiological triad- agent, host and environment. Operating in combination, these factors causes not only single case to epidemics, but also the distribution of disease in community.

Pathogenesis phase Begins with the entry of the disease “agent” in the susceptible host. The disease progresses through incubation period,early and late pathogenesis. Final outcome- recovery, death, disability.

The infection in the host may be clinical, sub- clinical; typical or atypical or the host may become carrier with or without having developed disease. (e.g. d iphtheria, poliomyelitis)

…………………… Natural history of disease is not Natural history of disease is not necessarily the same in all necessarily the same in all individuals individuals

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