Concepts of disease

August 30, 2016 PUBLIC HEALTH DENTISTRY- SRI SAI
COLLEGE OF DENTAL SURGERY
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GOOD
MORNING

August 30, 2016
PUBLICHEALTHDENTISTRY-SRI SAICOLLEGEOFDENTALSURGERY
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Concept of Disease
Presented by Dr. Hari prasad Gone
Guided by Dr.Monica Mam

contents
• Definition of disease
• Distinction between disease, illness, sickness
• Concept of causation-theories
• Epidemiological triad
• Multifactorial causation
• Web of causation
August 30, 2016 PUBLIC HEALTH DENTISTRY- SRI SAI COLLEGE OF
DENTAL SURGERY
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• Natural history of disease
• Spectrum of disease
• Iceberg phenomenon of disease
• Conclusion
• References
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by end of seminar You will be able
answer
• What is disease
• Why you need to study
• Why it occurs
• When it occurs
• How it progresses
• What is your role as epidemiologist
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• Disease the word itself has an negative vibe and recalls a
memory of suffering.
• Earlier disease was viewed as an curse or punishment for sins
committed by man i.e. it has its own fear factor.
• Later perceptions on disease were changed . It is now viewed as a
channel to explore more crevices in understanding human body
its capabilities, limitations, interactions etc.

Introduction
• Disease and health are relative components
• "Health is a state of complete physical, mental and
social wellbeing and not merely an absence of disease
or infirmity"- WHO 1948
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The definitions of disease seem to have varied with the prevailing
explanatory models of medicine.
Medicine has studied disease in terms of
 Disturbance of bodily homeostasis (Hippocrates, Galenus),
 Morphological changes in the internal organs (Morgagni),
 Tissues (Bichat) or cells (Virchow),
 The irritation of the organs and their reaction (Brown),
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 The invasion of the body of an external contagion (Koch) and
genetic alterations.
 Whereas ancient medicine defined disease as the disturbance
of humoral homeostasis.
 Medicine of the third millennium seeks to define disease in
the language of microscopic or radiographic morphology,
biochemistry and molecular biology.
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Webster defined disease as
• "a condition in which body health is impaired, a departure from a
state of health, an alteration of human body interrupting the
performance of vital functions”
• The Oxford English Dictionary defines disease as condition of the
body or some part or organ of the body in which its functions are
disrupted or deranged".
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• From an ecological point of view, disease is defined as
maladjustment of human organism to the environment.
• From sociological point of view, disease is considered as a
social phenomenon occurring in all societies.
• In simple words disease is -----.
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Disease: medical aspects
Sickness: social
Illness: personal

• Disease
• It can be described as physiological or psychological
dysfunction of the body(literally without ease- the
opposite of ease- when something is wrong with
bodily function)
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Illness
• It is a subjective state of the person who feels aware of not
being well.
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Sickness
• It is a state of social dysfunction .
• It can be described as inability to perform his ‘social role’/a
role that individual assumes when ill -- sickness role).
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WHO has defined health but not disease,
because of the following limitations?
• Disease has got many shades(spectrum0
• Onset – acute or chronic
• Healthy outside infect others carriers
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• The same pathogen - more than one disease (eg:streptococci).
• The same disease - more than one organism (e.g. diarrhoea).
• The course of the disease may be short or prolonged
• It is difficult to demarcate between normal and abnormal
state as in hypertension, diabetes, mental illness, etc.
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• The final outcome of the disease isvariable, i.e. recovery,
disability or death.
• Thus disease is a complex concept which is used as general
term but has more complex meaning and its exact definition
to set limits is under constant debate.
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Why do you need to know about
disease??

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Why does concept of disease
matters?
• Disease is a central notion to modern healthcare; it effects
society
• In order to decide who is entitled to treatment and to
economic rights, who is to be exempted from social duties
and who is morally accountable, and to decide what the
subject matter of medical science is.
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• Furthermore, a strictly, consistently and coherently defined
concept of disease could help the health care system face its
basic economical, social, epidemological and ethical
challenges, and could clarify the goal and limit of medicine.
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Theories of causation
• They are categorised as
 Old theories and
 Modern theories
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Old theories
• The supernatural theory of disease. (e.g. curse of God; an
evils eye), the theory of humors, miasmatic theory of
disease, the theory of spontaneous generation, etc. The
Ayurveda ,chinese medicine etc----empirical causes
• (primitive ,religious )
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biogenesis (Omne vivum ex
vivo "all life from life")

Modern theories
• Modern theories
• germ theory
• multifactorial causation – socioeconomic, cultural,
genetic, psychological
• epidemiological triad (tetrad)/ecological triad
• Advanced epidemiological triad
• web of causation
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Germ theory
• Louis Pasteur demonstrated presence of bacteria in air.
• Robert Koch showed that anthrax was caused by bacteria.
• These discoveries shifted concept of disease causation from
empirical causes (e.g., bad air) to microbes as the sole
cause of disease.
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• The concept of cause embodied in the germ theory of
disease is generally referred to as a one-to one relationship
between causal agent and disease. The disease model
accordingly is
• Disease agent-------> Man-------> Disease
• The germ theory of disease, though it was a revolutionary
concept, led many epidemiologists to take one-sided view
of disease causation.
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Limitations of Germ Theory
• Why only some people suffer from the disease even after
exposure
• Why certain people carry pathogens but do not show
manifestations of disease
• Why a disease would be epidemic sometimes
• It does not take into account the multi-factorial causation
even in the diseases in which micro-organism is the
“necessary cause”.
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Epidemiological triad/ecological triad
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Agent
EnvironmentHost
Time

Epidemiological triad
Agents
• Biological
• Physical
• Chemical
• Mechanical
• Insufficiency or excess of factors, hormones, nutrients,
parts, structural defects, chromosomal factors,
immunological factors
• Social
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• Host
• Demographic
• Biological – genetic, biochemical, immunological,
physio functions
• Social and economic
• Lifestyle
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• Environment
• Physical,
• Biological,
• Psychosocial
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Theory of multifactorial causation
 Pettenkofer of Munich proposed this concept earlier to the germ
theory but the germ theory of disease overshadowed the multiple
cause theory.
 As a result of advances in public health, chemotherapy,
antibiotics and vector control communicable diseases began to
decline- only to be replaced by new types of diseases, the so
called modern diseases of civilization. e.g. lung cancer, coronary
heart disease, chronic bronchitis, mental illness, etc.
 Lung cancer, coronary heart disease, chronic bronchitis, mental
illness, etc. all of which cannot be explained by earlier theories.

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 These diseases cannot be explained on the basis of the germ
theory of disease nor can be prevented by the traditional methods
of isolation, immunization or improvement in sanitation.
 The realization began to dawn that the “single cause idea” was an
oversimplification and that there are other etiological factors-
social, economic, cultural, genetic and psychological which are
equally important.
 As already mentioned, tuberculosis is not merely due to tubercle
bacilli; factors such as poverty, overcrowding and malnutrition
contribute to its occurrence.

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For example,
 excess fat intake, smoking, lack of physical exercise, and obesity are
all the factors involved in the pathogenesis of Coronary Heart
Disease.
 Most of these factors are linked to lifestyle and human behaviour.
 Medical men are looking "beyond the "germ theory" and the multi-
factorial causation concept came into existence.

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 The term agent is replaced by causative factors which implies the
need to identify multiple causes or etiological factors of disease,
disability, injury or death.
 Why do you need to know associated multiple factors??
 The purpose of knowing multiple factors of the disease is to
quantify and arrange them in priority sequence for modification or
amelioration to prevent or control the disease.

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Advanced model of triangle of epidemiology

Risk factors and risk groups
• Risk factors
• Modifiable, non-modifiable
• Examples for CVD
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Risk groups
• Target groups
• Risk approach
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Web of causation
 This model of disease causation was suggested by Mac Mahon and
Pugh.
 This model is ideally suited in the study of chronic disease, where
the disease agent is often not known, but is the outcome of
interaction of multiple factors.
 The "web of causation" considers all the predisposing factors of
any type and their complex interrelationship with each other

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Web of causation

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 The web of causation does not imply that the disease cannot
be controlled unless all the multiple causes or chains of
causation or at least a number of them are appropriately
controlled or removed.
 Sometimes removal or elimination of just only one link or
chain may be sufficient to control disease, provided that link
is sufficiently important in the pathogenic process.
 In a multifactorial event, therefore, individual factors are
by no means all of equal weight.

Natural history of disease
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• The term Natural history of disease is a key concept in
epidemiology.
• It signifies the way in which a disease evolves over time
from the earliest stage of its prepathogenesis phase to its
termination as recovery, disability or death, in the
absence of treatment or prevention.

Natural history of disease
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Spectrum of disease
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Lord Yama’s given
spectrum of death

Iceberg phenomenon
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Iceberg of disease

Iceberg phenomenon
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August 30, 2016
PUBLIC HEALTH DENTISTRY- SRI SAI COLLEGE OF DENTAL SURGERY
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Finally what is our role??
 What the physician sees in the hospital is just an "episode" in the
natural history of disease.
 The epidemiologist, by studying the natural history of disease in
the community setting is in a unique position to fill the gaps in our
knowledge about the natural history of disease.

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Do you know???

conclusion
• Defining a disease is a complex on going debate an
adequate defintion explaining diffuse nature of disease is
yet to be found.
• Concept of disease and its comprehension by us is
everchanging since times immemorial from empirical
causes to evidence based or supported causes.
Understanding disease has progressed from studying
clinical cases to susceptibles that too molecular and gene
level.
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• Man has altered his physical environment to reduce
infectious diseases mortality to a great extent only to get
them replaced by chronic or modern also called lifestyle
diseases. Man today viewed as an “agent” of his own
diseases. Today man lives long enough to get affected by
chronic diseases unlike in earlier generations where
mortality at younger age was more due to infectious
diseases.
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DENTAL PUBLIC HEALTH SIGNIFICANCE
• The epidemiologist, by studying the natural history of
disease in the community setting is in a unique position to
fill the gaps in our knowledge about the natural history of
disease.
• KNOWLEDGE OF DISEASE HOW WHY WHAT
WHENS aids in diagnosis prevention and management of
various diseases at a community level.
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References
 Preventive and social medicine 23rd edition- K.PARK
 Textbook of preventive and community dentistry- soben peter
 Community medicine with recent advances – A H Suryakantha
 Complexity of disease
 Term Lifestyle diseases have to be avoided
 Concept of disease

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 Vallagard S.Why the concept “ lifestyle diseases”
should be avoided,
 Scandinavian journal of public health , 2011 ; 39:
773-775.
 Alexandar c, tsai , bridget f.O., Burns . Syndemics
of psychological problems and HIV risk : A
systematic review of empirical tests of the disease
interaction concept , Social science & Medicine,
201 ;139 :26-35

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