1. NATURAL HISTORY OF DISEASE
EPIDEMIOLOGY / HIKMET QUBEILAT

2. 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.

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

4. 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

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

6. 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.

7. 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.

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

9. 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.

10. 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)

12. 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.