This document provides an overview of the natural history of disease. It discusses the key concepts including the pre-pathogenesis phase where disease exists in the environment prior to infecting humans, the pathogenesis phase where the disease agent enters the host and the disease progresses, and the epidemiological triad of agent, host, and environment factors that influence disease. It also examines risk factors that increase likelihood of disease, different types of risk groups, how diseases can present along a spectrum of severity, and the iceberg concept of disease where undetected cases exceed reported cases.

1. Natural History of Disease
Nishitha A
7th term

2. Objectives
• Introduction
• Phases
• Epidemiological Triad
• Factors causing disease: Agent, Environment,
Host
• Risk Factors
• Risk groups
• Spectrum of Disease
• Iceberg of Diseases

3. FAQ’s in RGUHS
• Natural history of Disease with stages
• Macroenvironment
• Risk Factors in Disease
• Epidemiological Triad
• Iceberg Phenomenon
• Spectrum of Disease

4. Introduction
• Natural history of disease refers to the
progress of a disease process in an individual
over time, in the absence of treatment or
prevention.
• Key concept in Epidemiology
• Each disease has its own, unique natural
history.

6. Phases of Disease
Disease
Process
Pre-Pathogenesis Pathogenesis

7. Pre-Pathogenesis
• Period of disease before man is involved
• Process of disease in the environment
• Man in the Midst of disease
• The disease agent has not yet entered man,
but the factors which favour its interaction
with the human host are already existing in
the environment.

8. Epidemiologic triad

10. 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 .

12. Agent
• A substance , living or non-living, or a force,
the excessive presence or relative lack of
which may initiate or perpetuate a disease
process.
• May be a single agent/combination of 2
independent agents

13. Types of Agents
Agents
Biological Nutrient Physical Chemical Mechanical Social

14. Biological Agents

15. Nutrient Agents

16. Physical Agents

17. Chemical Agents
Endogenous Exogenous

18. Social Agents

19. Host factors
Host Factors
Demographic
Biological
Socio-economic
Lifestyle

20. Host Factors

21. Environmental Factors
Environment
Physical Social Psychosocial

22. Macro-environment
All that which is external to the
individual human host, living and
non-living, and with which he is in
constant interaction.

23. Physical Enviroment

24. Biological Environment

25. Psychosocial Environment

27. Risk Factors
• Applicable to those diseases where the
disease agent cannot be established.
• Definition : An attribute or exposure that is
signifiantly associated with the development
of a disease.
• Presence of a risk factor disease will occur
• Absence of a risk factor absence of disease

28. Risk Factors- Types
Modifiable
Unmodifiable

29. Risk Factors

30. Prominent Risk Factors- Heart Diseaes

31. Risk Groups

32. Spectrum of Disease

33. Spectrum of Disease

34. Iceberg Concept of Disease

36. References
• Park’s Textbook of Preventive & Social
Medicine – 23rd Edition
• www.googleimages.com