Post on 27-Jan-2017
Concept of Disease
Dr. Md. Salequr Rahman (Shuvo)MBBS, MPH (CM) NIPSOM
DR. SIRAJUL ISLAM MEDICAL COLLEGEdrmdshuvo@gmail.com
Illness
• Illness is a subjective state of a person who feels aware of not being well.
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Sickness
• Sickness is a state of social dysfunction, i.e., a role that the individual assumes when ill (“sickness role”).
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CONCEPT OF DISEASE
• It is a mal-adjustment of human organism to the environment.
• I t is deviation from normal function.
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NATURAL HISTORY OF DISEASE
• Disease results from a complex interaction between man, an agent & the environment.
• “NATURAL HISTORY OF DISEASE” is a key concept in epidemiology.
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• It is customary to describe the natural history of a disease as consisting of two phases;
1. PRE PATHOGENESIS PHASE. 2. PATHOGENESIS PHASE.
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1. THE PRE PATHOGENESIS PHASE
• This refers to the preliminary period to the onset of the disease in man.
• The disease agent has not yet entered man, but the factors which interaction with human host are already existing in the environment
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2. PATHOGENESIS PHASE
• The pathogenesis phase begins with the entry of the disease agent in the susceptible human host.
• The further events in the pathogenesis phase are clear cut in infectious disease.
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Risk factors of disease
The term risk factor is used by different authors withat least two meanings:1. An attribute or exposure that is significantly
associated with development of a disease2. A determinant that can be modified by
intervention thereby reducing the possibility of occurrence of disease
3. Many diseases such as cancer, coronary heart disease are still unidentified. Here etiology is discussed in terms of risk factors
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ContinuedThere are 2 types of risk factors:1. Modifiable2. Non modifiable
Modifiable risk factors• Smoking• Hypertension• Obesity• Decreased physical activity• Elevated cholesterol level drmdshuvo@gmail.com
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Continued…
Non modifiable risk factors• Age• Sex• Race• Family history• Genetic factors
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Iceberg of DiseaseThe iceberg phenomena refer
to the relationship between the symptomatic (diagnosed) cases with that of pre-symptomatic (undiagnosed) cases. It is represented by a iceberg; which has a floating tip, a submerged portion and a demarcation line in between
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Iceberg of DiseaseFloating tip: Represents what the
physician sees in the community i.e. clinical cases Submerged portion: Represents what the physicians can not see in the community or the hidden mass of infection or disease i.e. inapparent, pre-symptomatic, undiagnosed, latent, subclinical cases & carriers in the community Waterline: Represents the demarcation between clinical & subclinical cases
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Iceberg of DiseaseIcebergs reveal only about one-tenth (1/10th)
of their mass above the water. The remaining nine-tenths (9/10th) remain
submerged
Importance
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THEORIES OF DISEASES CAUSATION
1. Supernatural theory of disease– Disease is due to super power e.g. gods, evil
spirits. 2. Tridosha theory of disease
– The doshas or humors are: Vaata (Wind), Pitta (gall), and Kapha (mucus).
– Perfect balance of tridosha is healthy – Disturbance in balance is disease
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THEORY OF DISEASES CAUSATION
3. Theory of Contagion– Spreading of disease by being close to or
touching other people. 4. Miasmatic theory of disease causation
– Disease is due to noxious air and vapors– These concepts were prevailing before
Louis Pasteur (1822-1895).
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THEORY OF DISEASES CAUSATION
5. Germ Theory of disease– In 1860, Louis Pasteur demonstrated the
presence of bacteria in air. – This theory emphasized that the sole cause
of disease is microbes. – The theory generally referred to as one-to-
one relationship between disease agent and disease.
Disease agent Man Disease
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THEORY OF DISEASES CAUSATION
6. Epidemiological Triad concept – The germ theory of disease has many
limitations – For example it is well – known that not all
exposed to tuberculosis bacilli develops tuberculosis ,the same condition in an undernourished person may result in clinically manifest.
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MULTI-FACTORIAL ETIOLOGY
• The germ theory of disease or single cause of disease is always not true.
• The germ theory of disease was overshadowed by multi-factorial cause theory in 19th century.
• As a result of advancement in public health, communicable diseases began to decline and are replaced by new type of diseases so called modern disease of civilization.
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MULTI-FACTORIAL ETIOLOGY• Example: Lung cancer, CHD, Mental illness
etc. The disease could not be explained on the basis of germ theory of disease and can not be controlled or prevented on that basis. The realization began that multiple factors are responsible for disease causation where there is no clear single agent.
• The purpose of knowing multiple factors of disease is to quantify and arrange them in priority sequence for modification to prevent particular disease.
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• This model of disease causation was suggested by Mac Mohan 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 interaction with each other.
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WEB OF CAUSATION• The basic tenets of epidemiology are to study
the clusters of causes and combinations of efforts and how they relate to each other.
• The web of causation does not imply that the disease can not be controlled unless all the multiple causes or chain of causation or at least a number of them are appropriately controlled.
• Sometimes, removal of one link may be sufficient to control disease.
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WEB OF DISEASE CAUSATION
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Changes in life style Stress
Smoking
Obesity HTN
Emotional stress
Aging
Changes in the wallsof arteries Coronary Occlusion
Myocardial ischemia
Hyperlipidemia
Coronary Atherosclerosis
Myocardial Ischemia
Fig: Web of causation of MI
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