Theories of illness

1. THEORIES OF
DISEASE
CAUSATION

2. OPPOSITE TO
HEALTH
What is disease??

3. 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.

4. Definition of disease: (Cont.)
 “The condition of body or some part of organ of
body in which its functions are disrupted or
deranged” - Oxford English Dictionary

5. 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.

6. How disease is caused? (Cont.)
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.

7. Theories of Illness / Disease Causation
 Theories of disease causation:
1. Miasma theory.
2. Germ theory.
3. Epidemiological triangle.
4. Web of causation
5. The theory of general susceptibility.
6. The socio-environmental approach.

9. 1-Miasma Theory
 The word "miasma" comes from ancient Greek and
means "pollution".
 The miasma theory (also called the miasmatic
theory) is an obsolete medical
theory that held that diseases—such as cholera, or
the Black Death—were caused by a miasma a
noxious form of "bad air", also known as night air.
 The theory held that the origin of epidemics was
due to a miasma, emanating from rotting organic
matter.

10. Miasma Theory (Cont.)
 In the 1850s, miasma was used to explain the
spread of cholera in London and in Paris.
 In China, miasma was thought to be caused by the
heat, moisture and the dead air in the Southern
Chinese mountains. They thought that insects’
waste polluted the air, water.
 The miasma theory was consistent with
observations that disease was associated with poor
sanitation.

11. As a result of the miasma theory
The sanitary movement era
(The first half of the nineteenth century)
1. Public health measure were concerned with
sanitation.
2. Focus was on disease prevention (causes of
diseases in population) and the health needs of
poor population.
3. The epidemiology were largely involved in
population-wide health improvement.

12. 2. Germ Theory

13. Germ theory
 Germ theory was proposed by Louis Pasteur (1822 –
1895) and Robert Koch (1843 –1910).
 Germ theory postulates that every human disease is
caused by a microbe or germ, which is specific for that
disease and one must be able to isolate the microbe
from the diseased human being.

14.  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).

16. 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.

17. 3. 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.

18. Bacteria
Viruses
Fungi
Age
Sex
Health Behavior
Immunity
Genetic makeup
Air
Water
Sanitation
Noise

19. As a result of the epidemiological triangle theory:
 It was believed that diseases can be prevented by
modifying factors which influence exposure and
susceptibility.
 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.

20. 4. 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.

22. Cause
Cause
Cause
Cause
Effect Disease

23. 5. 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.

24. Examples:
Low social class
Lung
Cancer
Respiratory
disease
Cerebro-vascular
disease
Ischemic heart
diseases
Higher
rates

25. Examples (Cont.):
African American
Hypertension
Dementia
Stroke
Diabetes (NIDD)
Prostrate
cancer
Higher risk group

26. 6. 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.

28. Factors that improve people’s health:
Based on the socio-environmental approach, five
broad factors that can be targeted in order to
improve population health :
 The General socioeconomic cultural and
environmental conditions
 The physical environment.
 Social and community networks
 Individual lifestyle factors
 Age sex & Hereditary Factors

29. 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.