CONCEPT OF CONTROL OF DISEASE

1. CONCEPT OF
DISEASE
DR. MAHESWARI JAIKUMAR
maheswarijaikumar2103@gmail.com

2. DISEASE
• Disease is a
physiological /
psychological
dysfunction.

3. • Illness is a subjective state of a
person who feels aware of not
being well.
• Sickness is a state of social
dysfunction, i.e., a role that the
individual assumes when ill
(“sickness role”).

4. CONCEPT OF CAUSATION
• Germ Theory of
Disease.
• Epidemiological triad.
• Multi factoral
causation.
• Web of causation.

5. GERM THEORY OF DISEASE
• This concept gained
momentum during the 19th
• The disease model
accordingly is as follows.

6. WEB OF CAUSATION
Disease
agent
Man Disease
The concept of cause embodied in the
germ theory of disease is referred to
as a one-to-one relationship between
causal agent and disease

7. WEB OF CAUSATION

8. EPIDEMIOLOGICAL TRIAD
• The germ theory has many limitations.
• It is well known that not everyone
exposed to tuberculosis develops
tuberculosis, however in an
undernourished or otherwise
susceptible person may result in
clinical disease.

9. • There are other factors relating to the
host & environment which are equally
important to determine whether or not
disease will occur in the exposed host.
• This demanded a broader concept of
disease causation that synthesized the
basic factors of agent, host, &
environment

10. AGENT HOST
ENVIRONMENT
EPIDEMIOLOGICAL TRIAD

11. • The Agent, Host, Environment
model has been in use for many
years.
• It has helped epidemiologist to
focus on different classes of factors
especially with regard to infectious
diseases

12. MULTIFATORIAL CAUSATION
• Pettekofer of Munich (1819 – 1901)
propounded the concept of multi
factorial causation.
• Modern diseases such as coronary heart
diseases, chronic bronchitis, mental
illness could not be explained by the
germ theory of disease.

13. MULTI FACTORIAL CAUSATION

14. • This realization began to draw that a
single cause idea was an over
simplification & that the other
factors in the etiology of disease –
social, economic, cultural, genetic &
psychological which are equally
important.

15. • E.g., Tuberculosis is not merely
due to tubercle bacilli; factors
such as poverty, overcrowding &
malnutrition contribute to its
occurrence.

16. • The purpose of knowing the
multiple factors of disease is to
quantify and arrange them in
priority sequence for modification
or amelioration to prevent or
control disease.
• The multi factorial causation offers
multiple approaches for the
prevention control of disease

17. WEB OF CAUSATION
• Mac Mahon & Pugh suggested this
theory.
• This model is ideally suited for the
study of chronic diseases where
disease agent is often not known, but
is the outcome of interaction of
multiple factors.

18. • The web of causation considers all the
predisposing factors of any type & their
complex interrelationship with each
other.
• The causal web provides a model
which shows a variety of possible
interventions that could be taken
which might reduce the occurrence of
the disease.

19. • Some times 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.
• The relative importance of theses
factors may be expresses in terms of
“relative risk”.

20. 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.

22. • It signifies the way in which the
disease evolves over time from
the earliest stage of its pre
pathogenesis phase to its
termination or prevention.
• Each disease has its own unique
natural history.

23. • It is customary to describe the
natural history of a disease as
consisting of two phases;
1. PRE PATHOGENESIS PHASE.
2. PATHOGENESIS PHASE.

24. 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
favour interaction with human host
are already existing in the
environment

25. • This situation is referred to as
“man in the midst of disease”.
• The causative factors of disease
may be classified as agent, host &
environment.
• These factors are referred to as
EPIDEMIOLOGICAL TRIAD”.

26. • The mere presence of these
factors is not sufficient to start
the disease.
• What is required is the
interaction of these three
factors.

27. 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.

28. • The agent multiplies & induces tissue &
physiological changes, the disease
progresses through a period of
incubation & later through early & late
pathogenesis.
• The final outcome of the disease may
be modified by intervention measures
such as immunization & chemotherapy.

29. COURSE OF DISEASE

30. AGENT FACTORS
BIOLOGICAL AGENTS

31. BIOLOGICAL AGENTS
• Virus, bacteria, rickettsiae, fungi,,
protozoa & metazoa.
• These agents exhibit certain host
related biological properties such
as

32. CHARACTERISTICS OF AGENT
FACTORS
INFECTIVITY : Ability of the infectious
agent to invade & multiply in
a host.
PATHOGENECITY : Ability to induce
clinically apparent
illness .

33. • VIRULENCE : The proportion of
clinical cases
resulting in severe
clinical manifestations.

35. NUTRIENT AGENT
• These are proteins, fats,
carbohydrates, vitamins, minerals &
water.
• Any excess or deficiency of the
intake of nutritive elements may
result in nutritional disorders,

36. • PEM, anaemia, goitre, obesity &
vitamin deficiencies are some of
the current nutritional problems
in our country.

37. PHYSICAL AGENT
• Exposure to excessive heat,
cold, humidity, pressure,
radiation, electricity, sound,
etc may result in illness

38. CHEMICAL AGENTS
• ENDOGENOUS : Some of the
chemicals may be produced in the
body as a result of derangement of
function, e.g., urea (ureamia),
serum bilirubin (jaundice), ketones
(ketosis), uric acid (gout), calcium
carbonate (kidney stones), etc.

39. • EXOGENOUS : Agents arising
outside of human host, e.g.,
allergens, metals, fumes, dust,
gases, insecticides, etc. These
may be acquired by inhalation,
ingestion or inoculation

40. MECHANICAL AGENTS
• Exposure to chronic friction &
other mechanical forces may
result in crushing, tearing,
sprains, dislocations & even
death.

41. ABSENCE OR
INSUFFICIENCY OR
EXCESS OF A FACTOR
NECESSARY TO HEALTH

42. • These may be Chemical factors :
hormones (insulin,oestrogens),
Nutrient factors : iron deficiency,
Lack of structure : Thymus, Lack of
part of structure: Cardiac defects,
Chromosomal factors :
Mongolism,Dawn
Syndrome,Immunological factors :
Agammaglobulinaemia

43. SOCIAL AGENTS
•The social agents are
poverty, smoking, alcohol,
unhealthy life styles, social
isolation, maternal
deprivation, etc.

44. HOST FACTORS
• The host factors may be classified as :
• 1. Demographic characteristics such
as age, sex, ethnicity.
• 2. Biological characteristics such as
genetic factors, bio chemical levels
of the blood (cholesterol).

45. • 3. Social & Economic
characteristics such as education,
occupation, stress, marital status,
housing.
• 4. Life style factors such as
personality traits, living habits,
physical exercise, use of alcohol,
drugs, smoking.

46. ENVIRONMENTAL FACTORS
• The study of disease is really the
study of man & his environment.
• The environment can be classified as
Internal & external environment. The
external or the macro environment is
defined as all that which is external
to the individual human host. They
are categorized as follows.

47. •1. Physical environment.
•2.Biological environment.
•3.psychosocial environment.

48. PHYSICAL ENVIRONMENT
• The term “physical environment” is
applied to non living things &
physical factors. (air, water, soil,
housing, climate, geography, heat,
light, noise, debris, radiation,
etc.)with which man is in constant
interaction.

49. • Man’s victory over his physical
environment has been responsible for
most of the improvement in health
during the past century.
• However this has added to a host of
other problems like air pollution, noise
pollution, urbanization, radiation
hazards etc, human exposure to
electromagnetic energy, etc.

50. BIOLOGICAL ENVIRONMENT
• The biological environment is the
universe of living things which
surrounds man.
• The living things are bacteria,
virus, insects, rodents, animals &
plants.

51. • These are constantly working for
their survival, in this process some
of them act as disease producing
agents, reservoirs of infection,
intermediate hosts & vectors of
disease.
• When the harmonious relationship
is disturbed, ill health results.

52. PSYCHOSOCIAL ENVIRONMENT
• The psychosocial environment
encompasses cultural values, customs,
habits, beliefs, attitudes, morals, religion,
education, lifestyles, community life,
health services, social& political
organization.
• Man is in constant interaction with that
part of the social environment known as
“people”.

53. • He is a member of a social group.
• The behaviour of a person can affect
another.
• Conflict & tension between
members of a group can yield a
great distress. The impact of social
environment has both positive &
negative aspects on the health of
individuals.

54. • A favorable psycho social
environment has both positive &
negative aspects on health of
individuals & communities.

55. Psychosocial factors can also affect
negatively man’s health & well being.
For example poverty, urbanization,
migration & exposure to stressful
situations such as bereavement,
desertion, loss of employment, birth of
a handicapped child may produce
feelings of anxiety, depression, anger,
frustration & so forth.

56. • Man today is viewed as an
“agent” of his own disease. His
state of health is determined
more by what he does to himself
than what some outside germ or
infectious agent does to him.

57. THANK YOU