The document discusses the "iceberg concept" or "iceberg phenomenon" of disease occurrence in a population. It represents the burden of disease, with the visible tip representing clinically apparent cases but most of the iceberg submerged and representing latent, subclinical, undiagnosed, and carrier states in the population. Factors like the agent, host, and environment determine the size and shape of the iceberg. The iceberg concept is useful for detecting subclinical cases, understanding disease pathogenesis and spread, and designing control programs targeting the larger hidden reservoir of disease.

1. EPIDEMIOLOGIST
1/10
Clinician
Disease Iceberg
Represents Burden of the
Disease in a population
Latent,
subclinical,
undiagnosed &
carrier states in
the community/
population
By:
Dr. Bhoj R Singh
Epidemiology, IVRI,
Izatnagar

2. Iceberg concept of disease
occurrence
Methods to measure Severity & Prevalence
of Disease in a population
The analogy of an iceberg is used to describe the disease pattern in the
community or the population.
The study of the "iceberg phenomenon of a disease“ tells of the progress
(pathogenesis and spread) of a disease from its sub-clinical stages to apparent
disease state.
The tip of the iceberg represents what the clinicians see and submerged is the
part explored and made visible by the epidemiologists.
The large hidden part of the iceberg is what constitutes the mass of
unrecognized disease in the population and determines the fate of any disease
control program.

3. Clinical cases
Sub-clinical cases
Disease free group
Diseases like hypertension,
diabetes, anemia, malnutriti
on, parasitic infestation,
cancers and infectious
diseases like Johne’s
disease with little known
morbidity are presented by
large submerged portion of
iceberg. Similar is the case
with detection and control
undiagnosed reservoir of
disease and are real
challenge to modern
technique for elucidation of
the iceberg under cover.

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

5. Size & shape of Iceberg of a disease depends
upon
1. Agent-host-environment relationship
2. Natural history of disease(pathological
condition to complete recovery)
Virulence
Pathogenisity
Resisatnce
succeptibility
Temperature
Moisture etc.

6. Factors determining the size of a
disease iceberg in a population
• Agent Factors
– Virulence, genetic drifts & shifts, adaptability, host range, survivability
• Environmental factors
– Indoor environment
– Outdoor environment
• Host Factors:
– Genetic make up
– Early life events
– Immunological status (vaccination, innate, acquired)
– Occupation/ use
– Companions
– Other concurrent diseases/ infections etc.

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

8. Non- infectious diseases
• Mostly metabolic diseases/ disorders.
• Cardiac problems, Diabetes mellitus,
hypothyroidism, hypertension etc. (mostly in
dog), milk fever (in cattle).
• Production problems.
• Nutritional deficiency disorders.

9. How to determine in-apparent cases
• Screening surveys: It is the search for
unrecognized disease/sub-clinical disease in a
population by means of rapid test.
• Early detection of disease (prescriptive
screening)
• Whole population (mass screening)
• Target population (strategic screening)
• Rapid and reliable test (high specificity and
sensitivity)

10. 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.
Mistakes made by epidemiologist while
making an iceberg model

11. 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

12. Uses of Iceberg Concepts in
Disease Control
Primary
Prevention
Secondary
Prevention Tertiary
Prevention
Before
Occurrence/ entry
of disease
-Population strategy
-High Risk strategy
e.g. Tran-boundary
measures, Import
prohibitions,
Vaccination,
iradication
At incipient stage
of disease
-Screening case
finding, treatment
isolation. Less
effective, painful
e.g. Glanders and
Avian Flu, FMD &
Brucella
vaccination
When disease
is in outbreak
form.
Sanitation,
education,
social
measures
(movement
restrictions.

13. Prevalence
• 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 getting infected

14. Types
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 at risk at that point in time
• To study of chronic disease in a population

15. 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)
Number of people in the population during this period
• Longitudinal study
• Suitable for acute diseases
Life time prevalence
Number of individuals having diseases at least part
of their life

16. 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

17. Quiz
• Define iceberg model of disease occurrence.
• Give ice-berg model for Infertility in cattle, PPR in Goats &
Blue Tongue in Sheep.
• How will you use iceberg model for control of Brucellosis in
pigs.
• Give ice-berg strategy to control FMD.
• How ice-berg strategy differs from conventional disease
control methods?
• List the important diseases of animals and birds with inverted
iceberg model.