1. The document discusses the concept of disease and the natural history of disease. It defines disease and explores theories of disease causation such as the miasma theory, germ theory, and epidemiological triangle. 2. The natural history of disease refers to the progression of a disease from exposure to recovery, disability, or death in the absence of treatment. It involves stages of susceptibility, subclinical disease, clinical disease, and disability. 3. The document also discusses levels of disease prevention - primary, secondary, and tertiary - and how they relate to the stages of natural history and points of intervention.

1. Community Medicine
Concept of disease
Dr. Gahayr
25/10/2022
Lec-3

2. OBJECTIVES:
By the end of this lecture students should understand:
1- Concept of disease
2- The definition of natural history of disease.
3-Phases of natural history of disease.
4- Levels of disease preventions and their consequences .
5- The importance of natural history of disease.

3. What is disease??
ANS: opposite to Health
Definition of disease:
“A condition in which body function is impaired, departure from a state of
health, an alteration of the human body interrupting the performance of the
vital functions.”
- Webster.
“The condition of body or some part of organ of body in which its functions
are disrupted or deranged”
- Oxford English Dictionary

4. How disease is caused?
Before the rise of modern medicine, disease was attributed to a variety
of spiritual or mechanical forces, including:
A punishment from God for a sinful behavior.
Weak moral character.
Witchcraft.
However, these disease causation interpretations were challenged and
changed as the theories of disease causation was developed, changing
people’s views of diseases as related to specific agents and other
environmental factors.
The actual causation of particular forms of disease is in many cases
obscure, because of the limitations of our present knowledge.

5. Theories of disease causation
 Miasma theory.
 Germ theory.
 Epidemiological models of disease.
 Web of causation.
 The theory of general susceptibility.
 The socio-environmental approach.

6. Miasma theory
Miasma Theory : The word "miasma" comes from ancient Greek and
means "pollution“ that caused illnesses.
E.g In the 1850s, miasma was used to explain the spread of cholera in
London and in Paris.
The miasma theory was consistent with observations that disease was
associated with poor sanitation.
As a result of the miasma theory :The sanitary movement era, and
Public health measure were concerned with sanitation.

7. Germ theory
Health problems were believed to be the product of living organisms
which entered the body through food, water, air or the bites of insects
or animals.
It was believed that each disease has a single and a specific cause
(mono-causal approach).
The result of the Germ Theory: Researches were moved from the
community to the laboratory and concentrated on the identification of
agents for a given disease.
Medical practice became devoted to the destruction or eradication of
the agent from individuals already affected.

8. Epidemiological triangle
• According to this theory, exposure to an agent does not necessarily lead to
disease.
• It was believed that disease is the result of an interaction between agent, host
and the environment.
• Health Behavior, Immunity, Sex, Age, Genetic makeup, Noise, Bacteria, Air,
Viruses, Water, Fungi, and Sanitation.
• As a result of the epidemiological triangle theory:
It was believed that diseases can be prevented by modifying factors which
influence exposure and susceptibility.

9. Cont..
• This is useful in understanding infectious disorders, but less useful in
dealing with chronic, degenerative diseases such as heart diseases
and diabetes. For these disorders there is no specific agent that could
be identified against which individual and population may be
protected.

10. Web of causation
• According to this concept, disorders are developed through complex
interaction of many factors.
• These factors maybe biophysical, social or psychological and may promote
or inhibit the disease at more than one point in the causal process.
Ultimately, they determine the level of disease in a community.
• As a result of this theory: Based on this theory, it is believed that
prevention offers a better prospects for health than cure, since many of
these factors can be modified.
• Since several factors contributes to several diseases, community efforts
were shifted to factors modification (prevention) rather than disease
treatment.

11. Theory of general susceptibility
• This theory is not concerned with identifying single or multiple risk factors
associated with specific disorders. It seeks to understand why some social
groups seems to be more susceptible to disease and death in general.
• This reflects an imperfectly understood general susceptibility to health
problems.
• Examples: Low social class -Higher rates Lung Cancer
Ischemic heart diseases, Respiratory disease,Cerebro-vascular disease.
• Examples (Cont.): African American- Higher risk group Diabetes (NIDD)
Hypertension, Stroke, Dementia, Prostrate cancer

12. The socio-environmental approach
• This approach is not so much concerned with the causes of disease, rather
it seeks to identify the broad factors that make and keep people healthy .It
is concerned with the population rather than individuals.
• Based on the socio-environmental approach, five broad factors that can be
targeted in order to improve population health :
The social and economic environment.
The physical environment.
Personal health practices.
Individual capacity and coping skills.
Health services.

13. Cont….
As a result of this theory:
Health actions shifted from the individual to the community as a
whole. Improving health requires political and regulatory actions to
modify social, economical and physical environment.

14. 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.

15. Natural History of Disease Timeline or stages
1- Susceptibility stage ( Pre-pathogenesis)
2-Subclinical disease stage (Pre-symptomatic stage)
3-Clinical disease stage (Onset stage)
4- Stage of disability or death stage (advanced disease stage).

21. ICEBERG PHENOMENON OF
DISEASE

22. LEVELS OF PREVENTION

33. LEVEL of PREVENTION PIONT of INETRVENTION Natural History of Disease
Primary Health promotion
Prevention of exposure
Prevention of disease
EXPOSURE
Secondary Early detection & Rx “ Screening”
( Prevention of clinical onset)
Early treatment
( Prevention of permanent damage)
Biological onset
Incubation period
Clinical onset
Tertiary Limitation of disability Permanent damage

34. THANK YOU
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