First MBBS Lectures

2. Specific learning Objectives
At the end of the lecture students should be able
to
 Define disease.
 Enumerate theories of disease causation
 Understand concept of epidemiological triad,
Multi-factorial causation & web of causation
 Understand concepts of Natural history of
disease, Spectrum of disease & Iceberg
phenomenon

3. Definition of Disease
 Webster “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.”
 Oxford English Dictionary – the condition of body or
some part of organ of body in which its functions are
disrupted or deranged.

4. Disease
 Ecological point of view disease is
defined A maladjustment of the human
organism to the environment
 The simplest definition of disease is
 Disease is just the opposite of health
 Any deviation from normal
functioning or state of complete
physical or mental well being

5. WHO
WHO has defined health but not
disease
Disease literally means
“Without ease” (Uneasiness)
Disease is opposite of ease

6. Disease: Concepts
• Disease # Illness # Sickness
• Disease: Without ease/ uneasiness
• Illness: It is a subjective feeling of not
being well.
• Sickness: - It is a state of 'social
dysfunction' when person assumes
'sickness role' and unable to perform
social role
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7. • Difficulties in defining disease
 Spectrum of disease (in-apparent to sever)
Onset acute or gradual
Carrier state
Single organism may cause many clinical
manifestation
Single disease may cause by many organism
Short duration or Prolong duration
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8. Impairment/Disability/Handicap
• Impairment: - It is the loss or abnormality of
physiological, psychological function, anatomical
structure or function
• Disability: - It is the inability to carry-out activities
relevant to age and sex
• Handicap: - It is the disadvantage due to impairment
or disability
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Loss of type writer job
Loss of right upper limb
Un able to hold an object

9. 9
Loss of Rt. Upper Limb Unable to hold an object Loss of Job

10. Historical Theories for
causation of disease
 “Supernatural causes”& Karma
 Theory of humors (humor means fluid)
 The miasmatic theory of disease
 Theory of contagion
 Theory spontaneous generation
 Germ theory
 Epidemiological Triad
 Multi-factorial causation
 Web of causation
………Supernatural to multi-factorial causes…
Environment
Agent Host

11. Epidemiological triad
Agent Factors
Host FactorsEnvironmental
Factors
TIME

12. Advance model of triangle of
epidemiology

13. Agent
 The disease agent is
A substance , living or non living, or a force,
tangible or intangible, the excessive presence or
relative lack of which may initiate or perpetuate a
disease process.
 Disease may have a single or a number of
independent agents or a complex of two or more
factors

14. Agent
 Biological agents- living agent of disease Bacteria,
Viruses, protozoa, fungi, rickettsia
 Nutrient agents- Protein, carbohydrate, vitamins,
minerals and water
Any excess or deficiency of the nutrient elements
may result in nutritional disorders, anemia, goiter,
obesity
 Physical agents –Exposure to excessive heat, cold,
humidity, pressure, radiation, sound

15. Agents
 Chemical agents- metal fumes, dust,
gases, insecticides
 Mechanical agents – exposure to chronic
friction and other mechanical forces
may result in crushing, tearing, sprains,
dislocations
 Social agents – poverty, smoking, abuse
of drugs, unhealthy life style, social
isolation

16. Host
 Human host is referred as soil and the
disease agent as seed
 Host factors play a major role in
determining the outcome of an individual's
exposure to infection
 Host factors
 Demographic - age, sex, race
 Biological – genetic factors
 Social and economic factors
 Lifestyle factors

17. Environmental factors
 All that which is external to the individual
human host, living or nonliving and with
which he is in constant interaction
This include all surrounding such as air,
water, food, housing etc
Physical environment
Biological environment
Psychological environment

18. Multi-factorial causation
 Pettenkofer of Munich was an early
proponent of this concept (1819-1901)
 Factors like Social, economic, cultural,
genetic & psychological are equally
important.

19. Web of causation
Model suggested by MacMohan
& Pugh
Suits for NCD
Outcome of interaction of
multiple factors

20. Web of causationChange in life style Stress
Abundance of food Smoking Emotional Aging &
D Disturbance other factor
Obesity Lack of physical activity Hypertension
Hyperlidemia Increase catacholamine Changes in walls of
arteries
thrombotic activity
Coronory atherosclerosis
Coronary occlusion
Myocardial Infarction
Myocardial Infarction

22. NATURAL HISTORY OF DISEASE
It is the way in which a disease evolves
over time from the earliest stage of its
pre-pathogenesis phase to its
termination as recovery, disability or
death, in the absence of treatment or
prevention

24. PRE-PATHOGENESIS PHASE
Period preliminary to the onset of
disease in man
The diseases agent has not yet
entered the man.
The factors which favour its
interaction with the human host are
already existing in the environment.

25. PATHOGENESIS PHASE
The pathogenesis phase
begins with the entry of the
disease agent in the
susceptible human host.

26. Natural History of Disease
Disease results from a complex
interaction between
man, agent and the environment

27. Natural History of Disease

28. Spectrum of health
 Health and disease lie along a continuum, and
there is no single cut off point
 The lowest point on the health-disease spectrum
is death and the highest point positive health
Positive health
Better health
Freedom from sickness
Unrecognized sickness
Mild sickness
Severe sickness
Death

29. The Health-Sickness spectrum

30. HEALTH AND ILLNESS

31. Spectrum of Disease
 Variation in the manifestations of disease
 Disease spectrum are sub clinical infections
(unidentified) to fatal illnesses
 Illnesses ranging in severity from mild to
severe

32. Disease in many Forms..
 Acute
 Chronic/insidious
 Carrier
Spectrum of disease

33. Iceberg of Disease

34. Iceberg of Disease
 Floating tip of the iceberg represents what the
physician sees in the community-clinical cases
 The vast submerged portion of the iceberg
represents the hidden mass of disease- latent,
inapparent, presymptomatic and undiagnosed
cases and carriers in the community
 Water line represents the demarcation between
apparent and inapparent disease

35. Subclinical Case: ICEBERG PHENONMENON
 E.gHIV, Polio etc

36. Thank
You………