description regarding sub clinical diseases which is real threat to a population

1. Iceberg concept of disease occurrence
Methods to measure prevalence in a population

2. EPIDEMIOLOGIST
1/10

3. Clinical cases
Sub-clinical
cases
Disease free group
Distribution of Heard

5. 1
2
3
4
5
Diagnosed and controlled
Diagnosed but not
controlled
Misdiagnosed
casesPopulation
at risk
Risk free
group

6. •The marginal cost of subclinical disease per infectious unit
is usually greater than the marginal cost of clinical disease
per infectious unit.
•This means that to prevent animal from non infectious
units to a burden of one infectious unit is higher than the
cost of increasing an already high infectious burden by
one unit.
E.g.- Relationship
between somatic cell
count and decrease in
milk production in case
of mastitis

7. • Iceberg model depends upon
1. Agent-host-environment relationship
2. Natural history of disease(Progression of disease process in
an individual over time)
Virulence
Pathogenisity
Resisatnce
succeptibility
Temperature
Moisture etc.

8. Infectious diseases
• Diseases with vast base-
1. Bovine paratuberculosis, Human
tuberculosis, Bovine lukemia virus, Mastitis
(sub-clinical cases)
2. Jhones disease, prion disease, HIV, rabies
(long ip)
3. Rickettsiosis (low specific and sensitive
diagnostic tests)
• Diseases with visible tip-
1. Tetanus, Anthrax, Clostridial infection (less
sub-clinical cases)
2 Staphylococcal food poisoning, pasteurellosis,
influenza (short ip)

9. Non- infectious diseases
• Mostly metabolic diseases
• Diabetes mellitus, hypothyroidism,
hypertension etc(mostly in dog), milk
fever (in cattle)

10. How can we detect sub-clinical
cases
SCREENING……..

11. Definition
• It is the search for unrecognized disease/sub-
clinical disease in a population by means of
rapid test

12. • Early detection of disease(prescriptive
screening)
• Whole population(mass screening)
• Target population(strategic screening)
• Rapid and reliable test(high specificity
and sensitivity)
• Economical in term of manpower and
materials
• Precise and repeatable
• Scientifically accurate

13. Mistakes made by epidemiologist

14. 1. Giving importance to ill animals
only
2. No clinical signs no disease
3. Only a single agent is cause of
infection
4. False interpretation of clinical
intervention
5. Dependency on clinical records

15. Uses –
• For detection of sub-clinical and
in apparent cases
• Treatment of in apparent cases
• Control of diseases with more
number of sub-clinical cases
• To have a detailed knowledge
regarding natural history of
diseases

16. Methods to measure
prevalence in a population

17. http://healthpowerforminorities.com/

18. • Prevalence is defined as number of
instances of disease or related
attributes in a known population, at a
designated time, without distinction
between old and new cases.
• Probability of having infection

19. 1. Point prevalence- Amount of disease
in a population at a particular point
of time
• Cross sectional/snap shot of the
disease
Number of individuals having a disease
at a particular point of time
Population Size
• Study of chronic disease

20. 2. Period prevalence-
Specified period of time(beginning +
number of new cases during that
period)
• Period prevalence =
Number of cases that occurred in a
given period(old + new)
Study Population Size
• Longitudinal type study

21. • Life time prevalence- Number of
individuals having diseases at least
part of their life

22. How to determine Prevalence
• By doing survey
• Survey may be of 2 types
1. Screening Survey
2. Questionnaire Survey

23. Screening Survey
• Survey is done using screening
• Rapid, simple, inexpensensive
• Can be used to detect disease on
a large scale
• Includes serological, biochemical,
haematological, physical
examination
• Helps in quantitative estimation of
prevalence

24. Questionnaire Survey
• Contains a series of questions
which are answered by the
respondent either in written
format or through verbal
communiucation
• Easy to perform, quick and less
man power needed
• But not reliable many times

25. Reference
• Concepts of Epidemiology: An integrated introduction to
the ideas, theories, principles and methods of
epidemiology by Raj S. Bhopal
• http://www.vetmed.wsu.edu/courses-
jmgay/EpiMod2.htm
• Veterinary Epidemiology by Michael Thrushfield
• Veterinary medicine and human health By CW Schwabe
• https://en.wikipedia.org/wiki/Prevalence
• http://health.knowledgeblog.org/2011/07/22/basic-
statistics-for-epidemiology/
• Principles of infectious disease epidemiology/
http://health.mo.gov/training/epi/Mod4StudentOutline.pd
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