NATURAL HISTORY OF DISEASE EPIDEMIOLOGY / HIKMET QUBEILAT

OBJECTIVES By the end of this lecture students should understand: 1-The definition of natural history of disease. 2-Phases of natural history of disease. 3- The importance of natural history of disease.

Natural history of disease refers to the progress of a disease process in an individual over time, in the absence of medical intervention.

This process starts from the moment of exposure of an individual to a casual agent that is capable of causing disease. In the absence of treatment or prevention (intervention), this process ends with recovery ,disability, or death

The natural history of disease consist of two phases:- 1- Pre-pathogenesis phase. 2- Pathogenesis phase.

1- pre-pathogenesis phase This is the period before the onset of disease (the agent has not yet entered man), but factors favoring its interaction with the human host are already existing in the environment.

The causative Factors of disease are classified as:- 1- AGENT(cause of disease). 2-HOST(man). 3- ENVIRONMENT. Disease results from interaction between these three factors.

Concept of Disease causation Epidemiologic Triad Disease results from interaction between: Agent Host Environment

2- Pathogenesis phase This phase begins with entry of the disease agent in the susceptible host (man) and it multiplies there and causes disease. THE FINAL TERMINATION OF DISEASE MAY BE:- 1-RECOVERY. 2-DISABILITY. 3-DEATH.

PERIOD OF PATHOGENESIS THE NATURAL HISTORY OF A DISEASE STIMULUS to the HOST HOST REACTION RECOVERY interrelation of Agent, Host and Environmental factors Latent Period (Pre-symptomatic) Symptoms, Signs(Clinical) with or without Defects, Disability PREPATHOGENESIS PERIOD OF PATHOGENESIS Health Promotion Specific Protection Early Diagnosis and Prompt Treatment, Disability Limitation Rehabilitation PRIMARY PREVENTION SECONDARY PREVENTION TREATMENT TERTIARY PREVENTION (Leavell's Level of Application of Preventive Medicine)

Importance of studying Natural history of disease The understanding of this progression from disease onset to cure or death is important for epidemiologists. Natural history is as important as causal understanding for the prevention and control of disease. The earlier you can become aware of the disease the more likely you will be able to intervene and save lives.