EPIDEMIOLOGIST

1/10

Clinician

Disease IcebergRepresents Burden of the

Disease in a population

Latent,

subclinical,

undiagnosed &

carrier states in

the community/

population

By:

Dr. Bhoj R Singh

Epidemiology, IVRI,

Izatnagar

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.

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.

1

2

3

4

5

Diagnosed and

controlledDiagnosed but

not controlled

Misdiagnosed

casesPopulat

ion at

risk

Risk free

group

Size & shape of Iceberg of a disease depends

upon

1. Agent-host-environment relationship

2. Natural history of disease(pathological

condition to complete recovery)

VirulencePathogenisity

Resisatncesucceptibility

TemperatureMoisture etc.

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.

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)

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.

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)

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

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

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.

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

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

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 prevalenceNumber of individuals having diseases at least part

of their life

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

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.