Community Health
CHS 212
THEORIES OF
DISEASE
CAUSATION
MS. SAMAH ALAGEEL
Outline:
 Definition of disease.
 The gradual development of disease causation:
 Miasma theory.
 Germ theory.
 Epidemiological models of disease.
 Web of causation.
 The theory of general susceptibility.
 The socio-environmental approach.
 Conclusion.
What is disease??
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.
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
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.
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.
How disease is caused? (Cont.)
 Theories of disease causation:
o Miasma theory.
o Germ theory.
o Epidemiological triangle.
o Web of causation
o The theory of general susceptibility.
o The socio-environmental approach.
Miasma Theory
 The word "miasma" comes from ancient Greek and
means "pollution".
 Miasma was considered to be a poisonous vapor or
mist filled with particles from decomposed matter
(miasmata) that caused illnesses.
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.
As a result of the miasma theory
The sanitary movement era
(The first half of the nineteenth century)
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.
1.
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.
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
Sex
Genetic makeup
Immunity
Age
Noise
Bacteria
Air
Viruses
Water
Fungi
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.
 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.
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.
Cause
Cause
Effect \ Disease
Cause
Cause
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.
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
Lung
Cancer
Respiratory
disease
Higher
rates
Cerebro-vascular
disease
Ischemic heart
diseases
Examples (Cont.):
African American
Higher risk group
Hypertension
Dementia
Diabetes (NIDD)
Stroke
Prostrate
cancer
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.
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 social and economic environment.
 The physical environment.
 Personal health practices.
 Individual capacity and coping skills.
 Health services.
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.
Conclusion
 As briefly described, it is clear that the role attributed
to the physical, social and psychological environment
increases as we have progressed from the germ theory
to socio-environmental models of health.
 The idea of diseases causation have moved from one
specific etiology to a broad non-specific multi factors
that are seen to be associated with a variety of disease
outcomes and ultimately the health and wellbeing of
the population.
The actual causation of particular
forms of disease is in many cases
obscure, because of the limitations of
our present knowledge.
Now its time to do it yourself…
Depression
Hypertension
Obesity
Malnutrition
Lung cancer