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
6
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
7
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
8
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
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
21.
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
23.
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.
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
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
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
