This document discusses various theories of disease causation. It begins by describing early theories that attributed disease to spiritual or imbalanced bodily elements. It then outlines several modern epidemiological theories: the germ theory that identified microorganisms as causal agents; the epidemiological triangle emphasizing interactions between an agent, host, and environment; and multi-factorial causation theory applying to chronic diseases with multiple interacting factors. Later theories discussed include the web of causation model and Diver's epidemiological model focusing on factors influencing health. The document also covers principles of screening programs and evaluating their effectiveness.

1. THEORIES OF DISEASE
CAUSATION

2. INTRODUCTION
• Before the rise of modern medicine, disease was
attributed to a variety of spiritual or mechanical
forces.
• Interpreted as a punishment by God for sinful
behavior or the result of an imbalance in body
elements.
• In the Middle Ages and convincing evidence proved
that the disease was spread by water contaminated
by the excretions of cholera victims.
• Before the discovery of micro-organism several
theories explaining the cause of disease were put
forward time to time

3. THEORIES:-
1. Super nature theory.
2. Germ theory
3. Epidemiological triangle
4. Multi-factorial causation theory
5. Web of causation
6. Diver’s epidemiological model.

4. 1. SUPER NATURE THEORY
• In the early past, the disease was thought
mainly due to either the curse of god or due
to the evil force of the demons.
• Accordingly, people used to please the gods by
prayers and offerings or used to resort to
witchcraft to tame the devils.

5. 2. GERM THEORY
• Became popular during 19th century and in earlier
20th century.
• This theory attributes micro-organisms as the only
cause of diseases.
• According to this theory, there is one single specific
cause of every disease.
• This refers to one to one relationship between the
causative agent and disease.
• This theory explains the origin of infectious-
communicable diseases.

6. For example-
• Diphtheria cause due to coryne bacterium
diphtheria, cholera due to vibrio choleae.
Agent
Man
DiseaseEffect
Cause

7. 3. THEORY OF EPIDEMIOLOGICAL TRIAD
• According to this theory, every one exposed to
disease agent did not contract the disease
• This model is also called as ecological model
and is involved through the study of infectious
diseases.

8. • According to this theory, there are three elements which are
responsible for particular disease causation.
A. AGENT
B. HOST C. ENVIRONMENT

9. 1. AGENT- is considered to be the primary factors.
e.g amoeba, bacteria, without which a particular
disease cannot occur.
2. HOST - Refer to human beings who came in
contact with the agent.
The host related factors which play an important
role are genetic makeup, age, sex, race, immunity,
health behavior etc.
3. ENVIRONMET – It includes all that is external to
the host and agent but that may influence
interaction between them.

10. These three factors as long as they remain in equilibrium or
balance, disease will not occur and is referred as state of health
equilibrium.
ENVIRONMENT

11. For example-
• Tuberculosis, all those who were exposed to the
tuberculosis organisms did not suffer from
tuberculosis.
• Only those who were undernourished, lived in dark
and dingy places and who did not have the
immunity against tuberculosis get the disease.
• This means it is not only the causative agent that is
responsible for disease but there are another factors
also, related to man and environment which
contribute to occurrence of disease.
• This leads to the theory of epidemiological triad.

12. 4. MULTIFACTORIAL CAUSATION THEORY
• Epidemiological theory is not applicable for non
infectious and chronic diseases like coronary artery
diseases etc. because it has many causes or
multiple factors.
• This theory helps to understand the various
associated causative factors, which suggests
preventive and plan measures to control the
disease.
• This leads to the theory of multi factorial causation.

13. Contd….
• This theory stress the multiplicity of interaction
between the host and environment.
• The models equally applicable to infectious disease
except that specific agents causing infectious and
non infectious diseases.
• The factorial causation model helps epidemiologist
to understand various associated causative factors,
prioritize these and plan preventive and control
measures for a particular disease.

14. • It is also found that several causative factors produce many
observed effects e.g air pollution, smoking, specific form of
radiation (causes) may produce lung cancer, emphysema and
bronchitis (effects).
EFFECT(DISEASE)
CAUSES
CAUSES
CAUSES

15. 5. WEB CAUSATION THEORY
• According to this concept disease never depends upon single
isolated cause rather it develops from a chain of causation in
which each link itself is a result of complex interaction of
preceding events these chain of causation which may be the
fraction of the whole complex is known as web of causation.
• The model is particularly applicable to chronic diseases
where the causative agent is unknown and which are due
interaction of multiple factors.
Example- Cardiovascular diseases, Cancer etc.

16. EXAMPLE….

17. 6. DEVER’S EPIDEMIOLOGIC MODEL
• The dever’s epidemiologic model is not so much
concerned with the causes of disease, rather it
focuses to identify the main factors that make
and keep people healthy.
• This model is composed of four major categories
of factors: human biology, lifestyle, environment
and health system.
• All these factors influence health status positively
or negatively.

18. CONTD…
• Human biology: it includes genetic inheritance,
complex physiological systems, factors related to
maturation and ageing.
• Life style factors: it includes daily living activities,
customs, traditions, health habits etc.
• Environmental factors: it includes physical, biological,
social and spiritual components.
• Health care system factors: it includes availability,
accessibility, adequacy and use of health care services at
all levels.

19. SCREENING
Introduction
• Historically the annual health examinations were meant for
the early detection of hidden disease.
• They are based on conserving the physician time for
diagnosis and treatment and having technicians to
administer simple inexpensive laboratory tests and operate
other measuring devices.
• This is the genesis of screening programmers. Today
screening is considers as a preventive care functions and
an extension of health care.

20. DEFINITION
Screening is defined as the search of unrecognized disease or
defect by means of rapidly applied tests, examination or other
procedures in apparently healthy individuals.
• SCREENING is testing for infection or disease in population
or in individuals who are not seeking health care.
For example- serological testing for AIDS virus in blood
donors, neonatal screening, pre-marital screening for
syphilis.

21. AIMS AND OBJECTIVES OF SCREENING:-
• To sort out from a large group apparently
healthy persons likely to have the disease.
• To bring those who are apparently abnormal
under medical supervision and treatment.

22. USE OF SCREENING
1. Case detection-
It is defined as presumptive identification of unrecognized disease, which
does not arise from a patient request.
• Example- neonatal screening.
• Disease sought by this method are bacteriuria in pregnancy, breast cancer,
cervical cancer, deafness in children, diabetes mellitus, iron deficiency
anemia etc. in this it is made sure that the treatment is started early.
2. Control of disease – It is also called prospective screening. The people are
examined for the benefit of others.
• Example- screening of immigrants suspected of having infectious diseases
such as tuberculosis and syphilis to protect home population.
• It leads to early diagnosis, permit more effective treatment and reduce the
spread of infectious disease.

23. CONTD…..
3. Research purposes- Screening is also done for research purposes.
• For example there are many chronic diseases whose natural history is not
fully known e.g cancer.
• So screening may be done in obtaining basic knowledge about the
natural history of such disease. The participants should be informed that
no follow-up therapy will be provided.
4. Educational opportunities- There is acquisition of information
of public health relevance.
• Screening programmers provide public awareness and education to
other health professionals.

24. TYPES OF SCREENING
1. MASS SCREENING –
It is the screening of the whole population or a subgroup to analysis whether or
not exposed to the risk of having the disease under study. It is not advisable
under limited sources.
2. HIGH RISK OR SELECTIVE SCREENING-
In this screening only those who are risk to have a particular problem or disease
e.g women 35+ and lower socioeconomic group have more chances of cancer
cervix and if they are screened for that, then more chances of detecting the
cases.
3. MULTIPHASE SCREENING-
It is application of two or more screening test in combination to large number of
people at once time than to carry out separate screening test for single disease.
For example, test for lung disease, cardiovascular diseases, diaetes, anemia,
kidney diseases, cancer of breast and uterus, visual and auditory defects are
group tougher. But it is an expensive venture and its benefits are under
question.

25. PRINCIPLES OF SCREENING:-
1. The condition should be an important health
problem.
2. There should be a treatment for the condition.
3. Facilities for diagnosis and treatment should be
available.
4. There should be a latent stage of the disease.
5. There should be a test or examination for the
condition.

26. CONTD…..
6. The test should be acceptable to the population.
7. The natural history of the disease should be adequately
understood.
8. There should be an agreed policy on whom to treat.
9. The total cost of finding a case should be economically
balanced in relation to medical expenditure as a
whole.
10. Case-finding should be a continuous process, not just a
"once and for all" project.

27. CHARACTERISTICS OF A GOOD SCREENING TEST
• Valid.
• Simple, accomplished easily and quickly.
• Reliable.
• Yield.
• Cost –benefit.
• Applicable and acceptable.
• Follow-up services.

28. CRITERIA FOR SCREENING
• The condition should be an important health problem.
• The natural history of the condition should be understood.
• There should be a recognizable latest or early symptomatic stage.
• There should be a test that is easy to perform and interpret,
acceptable, accurate, reliable, sensitive and specific.
• There should be an accepted treatment recognised for the disease.
• Treatment should be more effective if started early
• Diagnosis and treatment should be cost-effective.
• Case-finding should be a continuous process.

29. EVALUATION OF SCREENING PROGRAMMES
 Randomized controlled trials –
In this there will be one group which receives the screening test and a
control group which does not receive the test.
 Uncontrolled test –
It is used to if people with disease, detected through screening appear to
live longer after diagnosis and treatment than patients who were not
screened.
 Other methods-
Case control studies and comparison in trends between areas with different
degrees of screening coverage.

30. SUMMARY

31. CONCLUSION

32. REFERANCE
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communicable-and-non-communicable-disease.htm. >
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