DISEASE%20EPIDEMIOLOGY

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DISEASE EPIDEMIOLOGY
Dr . A.K.AVASARALA MBBS, M.D. PROFESSOR
HEAD DEPT OF COMMUNITY MEDICINE
EPIDEMIOLOGY PRATHIMA INSTITUTE OF MEDICAL
SCIENCES, KARIMNAGAR, A.P.. INDIA
91505417 avasarala_at_yahoo.com
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PROMPT

• DISEASE IS STILL A MYSTERY
• SOME DISEASES KILL AND SOME WONT KILL
• SOME ARE SHORT LIVED WHILE OTHERS ARE LONG LIVED
• SOME ARE TREATABLE AND SOME ARE NOT
• SOME ARE CURED BY MIRACLES
  (TO ACHIEVE SAINTHOOD, THERE ARE INSTANCES OF
  CURING BY MIRACLES)

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LEARNING OBJECTIVES

• THE STUDENT SHOULD LEARN DISEASE PROCESS
• WHAT IS DISEASE?
• WHAT ARE THE THEORIES OF CAUSATION OF DISEASE?
• HOW IS IT INITIATED?
• HOW IS IT CAUSED?
• HOW IS IT TRANSMITTED? HOW IT SPREADS?
• HOW IT IS DISTRIBUTED? AND WHY?
• HOW IT CAN BE PREVENTED?
• HOW IT CAN BE ERADICATED?

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PERFORMANCE OBJECTIVE

• STUDENT CAN USE EPIDEMIOLOGICAL APPROACH TO
  PREPARE A LESSON PLAN BY MAKING USE OF VON
  KIPLING'S SIX HONEST SERVING MEN (WHAT, WHY,
  WHEN, WHERE, WHOM AND HOW) TO DEVELOP A LECTURE

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WHAT EXACTLY IS A DISEASE IS STILL A ?

• IS IT A SEQUENCE OF PATHOLOGICAL CHANGES AND
  THEIR EFFECTS OCCURRING IN THE INDIVIDUAL?
• IS IT A COMPOSITE OF EFFECTS DUE TO DISTURBANCE
  IN MANS RELATIONSHIP WITH HIS ENVIRONMENT BY AN
  AGENT/FACTOR?

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WHAT IS A DISEASE?

• DISEASE CAN BE SIMPLY EXPLAINED
• AS DIS AT EASE OR ILL HEALTH
• SOME DESCRIBE IT AS DISTURBANCE IN EQUILIBRIUM
  BETWEEN MAN AND HIS TOTAL ENVIRONMENT.

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HOW THE DISEASE IS CAUSED?

• SUPERNATURAL THEORY OF DISEASE
• ECOLOGICAL THEORY
• GERM THEORY
• MULTIFACTORIAL CAUSATION THEORY

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NO UNANIMOUS OPINION

• AT LEAST 10 OF THE PEOPLE IN DEVELOPED
  COUNTRIES AND 30 IN DEVELOPING COUNTRIES STILL
  BELIEVE IN SUPERNATURAL ORIGIN
• EVEN TODAY SUPERSTITIONS ARE BECOMING MAJOR
  OBSTACLES IN DISEASE CONTROL
• MOST OF THE LITERATES VIEW THAT DISEASE IS THE
  RESULT OF MICROBES
• MOST OF THE UNEDUCATED PEOPLE (90) BELIEVE THAT
  DISEASE IS DUE TO BAD PHYSICAL ENVIRONMENT

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SUPERNATURAL THEORY OF DISEASE

• 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.

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ECOLOGICAL THEORY

• AROUND 463 BC, HIPPOCRATES IS THE FIRST
  EPIDEMIOLOGIST WHO ADVISED TO SEARCH THE
  ENVIRONMENT FOR THE CAUSE OF THE DISEASE.

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ENVIRONMENTAL INFLUENCE

• INTERACTIONS AMONG HUMANS, OTHER LIVING
  CREATURES, PLANTS, ANIMALS, MICRO ORGANISMS,
  ECOSYSTEMS, AND CLIMATE, GEOGRAPHY, AND
  TOPOGRAPHY ARE SO COMPLEX THAT DESPITE MUCH STUDY
  WE ARE OFTEN UNCERTAIN WHAT IS REALLY HAPPENING.

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ECOLOGICAL DETERMINANTS OF DISEASE

• MCKEOWN HAS POINTED OUT, IMPROVED HEALTH OWES
  LESS TO ADVANCES IN MEDICAL SCIENCE THAN TO THE
  OPERATION OF NATURAL ECOLOGICAL LAWS

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GERM THEORY

• Germ theory Microbes (germs) were found to be
  the cause for many known diseases. Pasteur,
  Henle, Koch were the strong proponents of
  microbial theory after they discovered the
  micro-organisms in the patients secretions or
  excretions.

ROBERT KOCH
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HENLE-KOCH POSTULATES

• Henle and Koch have postulated that
• Each disease will be caused by a germ
• Without that germ that disease will not be
  caused
• By introducing that germ , that disease can be
  caused in animals experimentally,
• And that germ can again be isolated from that
  sick animal experimented with.

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MULTIFACTORIAL CAUSATION THEORY

• PETTENKOFFER
• STATED THAT AGENT, HOST
  AND ENVIRONMENTAL FACTORS WILL ACT AND
  INTERACT SYNERGISTICALLY AND ACT AS
  JOINT INDEPENDENT PARTNERS IN CAUSING THE
  DISEASE.

PETTENKOFFER
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WHEN THE DISEASE OCCURS?
Agent (SEED) factors
DISEASE OCCURS ONLY WHEN THE HOST FACTORS AND
ENVIRONMENTAL FACTORS MAKE THE AGENT SUFFICIENT
ENOUGH TO CAUSE THE DISEASE
D
Environmental factors (SHOWER)
Host factors (SOIL)
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CAUSAL CONSTELLATIONS
disease

A F G H J K
A R S T X
A B C D E
A L M N P Q
Causal constellations 1
2 3
4
A NECESSARY CAUSE B TO X CAUSAL PARTNERS
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EXAMPLES

• LUNG CANCER IS CAUSED BY A CONSTELLATION OF
  CAUSES LIKE
• SMOKING
• UNFILTERED CIGARETTES
• 10 YEARS DURATION
• AND HOST SUSCEPTIBILITY

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TISSUE INSULT DUE TO CHRONIC IRRITATION

• Chronic irritation of any tissue may lead to
  disease
• MARJOLINS ULCER- in the past, barbers used to
  wipe their razors on their forearms frequently
  while shaving the beards of their clients. This
  chronic irritation has resulted in squamous
  epitheliomatous changes and cancers (
  Marjolins ulcers) in barbers

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PLANETS AND DISEASE

• IT IS WELL KNOWN THAT PLANETS (EARTH,SUN, MOON
  ) AND THEIR MOVEMENTS, THEIR INTER DISTANCES AND
  RELATIONSHIPS WILL CAUSE SEASONS OF THE YEAR
• PLANETS INFLUENCE ON ORIGIN OF SEASONAL
  DISEASES AND THEIR CONTROL IS STILL A PANDORA BOX

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INCUBATION

• THE AGENT INCUBATES TO ACQUIRE THE CRITICAL
  DENSITY TO INITIATE THE DISEASE
• IT MULTIPLIES OR INCREASES IN INTENSITY FOR A
  SPECIFIC PERIOD BEFORE BECOMING OVERT AND CLINICAL

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DISEASE INITIATION

• THE DISEASE IS INITITED
  AT THE CELLULAR LEVEL
  WHEN THE NECESSARY CAUSE (AGENT)
  BECOMES SUFFICIENT I.E. COMPLIMENTED BY ITS
  CAUSAL PARTNERS

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HOW IT PROGRESSES?

• Natural history of disease

Pre-pathogenic period
Incubation Period/Generation time
Disease initiation at Cellular level
Carrier State
Pathogenic period
Death
Convalescent period
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HOW THE DISEASE IS TRANSMITTED?
Susceptible Host/Non Immune/ Poor herd immunity
MODE OF TRANSMISSION THROUGH SOME VEHICLE OR
VECTOR
RESERVOIR/ SOURCE OF AGENT
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DISEASE DISTRIBUTION

• TIME DISTRIBUTION OF THE DISEASE
• SHORT TERM FLUCTUATIONS,
• LONG TERM FLUCTUATIONS,
• PERIODIC FLUCTUATIONS,
• CYCLICAL, SEASONAL, SECULAR TRENDS

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CLUSTERING

• THIS PHENOMENON IS USUALLY ASSOCIATED WITH
  INFECTIOUS DISEASES.
• DISEASE OCCURS IN CLUSTERS OR GROUPS AT A
  PARTICULAR PLACE WHEN THE PEOPLE ARE SUSCEPTIBLE
  AND ENVIRONMENT IS FAVOURABLE THERE.

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ONION PEEL PHENOMENON

• OLD DISEASES FADE AWAY GIVING PLACE TO THE NEW
  ONES
• JUST LIKE THE LAYERS OF THE ONION, THE OLD
  DISEASES WANE AND GIVE PLACE TO NEWONES.
• INFECTIOUS ONES WILL BE REPLACED BY
  NONINFECTIOUS ONES TO BE REPLACED LATER
• BY PERSONAL AND BEHAVIORAL PROBLEMS.

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DISEASE PREVENTION

• PRIMORDIAL PREVENTION-- INTERVENTIONS TAKEN
  BEFORE THE DEVELOPMENT OF RISK FACTOR
• PRIMARY PREVENTION -- INTERVENTIONS TAKEN
  BEFORE THE DISEASE IS ESTABLISHED
• SECONDARY PREVENTION-- INTERVENTIONS TAKEN AFTER
  THE DISEASE IS ESTABLISHED-
• TERTIARY PREVENTION --
• INTERVENTIONS TAKEN TO PREVENT
  COMPLICATIONS

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DISEASE SURVEILLANCE

• WATCHING THE DISEASE WITH SUSPICION, ATTENTION
  AND AUTHORITY
• SUSPECT UNLESS AND UNTIL IT IS DISPROVED
• BE ATTENTIVE AND CAUTIOUS
• TRY TO GRASP THE ENTIRE NATURAL HISTORY OF THE
  DISEASE

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PUBLIC HEALTH PROBLEM

• DISEASE WILL BE A PUBLIC HEALTH PROBLEM WHEN IT
  CAUSES HIGH MORBIDITY AND MORTASLITY
• DEMANDS URGENT HEALTH ACTION
• EITHER IN THE FORM OF
• CONTROL
• ELIMINATION
• ERADICATION

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DISEASE CONTROL

• CONTROL STRATEGY REDUCING THE MORBIDITY AND
  MORTALITY
• A CONTINGENCY TEMPORARY MEASURE IN CASE OF
  EMERGENCY

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DISEASE ELIMINATION

• NEAR ERADICATION STAGE
• INTERMEDIARY BETWEEN CONTROL AND ERADICATION
  STATUS
• LESS PUBLIC HEALTH PROBLEM
• BASED MAINLY ON SURVEILLANCE ACTIVITIES

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ERADICATION

• RADICLE MEANS MAIN ROOT OF A PLANT
• ERADICATION MEANS REMOVING ALONG WITH THE MAIN
  ROOT i.e. IN ENTIRETY
• ALL OR NONE FORMULA

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DISEASE ERADICATION
AGEENT IN RESERVOIROR SOURCE
MODE OF TRANSMISSION
SUSCEPTIBLEPOPULATION
TO ERADICATE THE DISEASE ONE MUST - ELIMINATE
THE RESERVOIR/SOURCE OF THE AGENT -
CUT OFF THE TRANSMISSION - MAKE THE PEOPLE IMMUNE
TO THAT DISEASE

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REFERENCES

• Last JM Public Health and Human Ecology, 2nd
  Edition. Stamford, CT Appleton Lange, 1998
  pp 8-9.Thucydides The Peloponnesian
  War. Translated by Rex Warner. Harmondsworth
  Penguin Classics, 1954 Book 2, Chapter 5, pp
  123-129
• For a good introduction, see for example McNeill
  W Plagues and Peoples. New York Doubleday, 1976
  
• Zinsser H, in Rats, Lice and History (Boston
  Little, Brown Co, 1935) gave a sparkling
  account of the influence of typhus on the outcome
  of wars. Diamond J, in Guns, Germs and Steel (New
  York Norton, 1997) strains credibility with a
  grand theory based on flimsy factual foundations
• Semmelweiss IP Die Aetiologie, der Begriff und
  die Prophylaxis des Kindbettfiebers. Pest, Wien
  und Leipzig CA Hartleben, 1861