Download Disease epidemiology

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
[email protected]
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)
LEARNING OBJECTIVES
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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?
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
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 MAN’S
RELATIONSHIP WITH HIS ENVIRONMENT
BY AN AGENT/FACTOR?
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.
HOW THE DISEASE IS CAUSED?
1. SUPERNATURAL THEORY OF
DISEASE
2. ECOLOGICAL THEORY
3. GERM THEORY
4. MULTIFACTORIAL CAUSATION
THEORY
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
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.
ECOLOGICAL THEORY
• AROUND 463 BC, HIPPOCRATES
IS THE FIRST EPIDEMIOLOGIST
WHO ADVISED TO SEARCH THE
ENVIRONMENT FOR THE CAUSE
OF THE DISEASE.
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.
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
GERM THEORY
ROBERT KOCH
• 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 microorganisms in the patients’
secretions or excretions.
HENLE-KOCH POSTULATES
Henle and Koch have postulated that
1.Each disease will be caused by a germ
2.Without that germ that disease will not
be caused
3.By introducing that germ , that disease
can be caused in animals experimentally,
4.And that germ can again be isolated from
that sick animal experimented with.
MULTIFACTORIAL CAUSATION
THEORY
PETTENKOFFER
• PETTENKOFFER
STATED THAT
AGENT, HOST AND
ENVIRONMENTAL
FACTORS WILL ACT
AND INTERACT
SYNERGISTICALLY
AND ACT AS JOINT
INDEPENDENT PARTNERS
IN CAUSING THE
DISEASE.
WHEN THE DISEASE OCCURS?
Agent (SEED) factors
D
Host factors (SOIL)
DISEASE OCCURS
ONLY WHEN THE
HOST FACTORS AND
ENVIRONMENTAL
FACTORS MAKE THE
AGENT SUFFICIENT
ENOUGH TO CAUSE
THE DISEASE
Environmental
factors
(SHOWER)
CAUSAL CONSTELLATIONS
disease
ABCDE
Causal constellations
1
AFGHJK
2
ALMNPQ
3
A = NECESSARY CAUSE
B TO X = CAUSAL PARTNERS
ARSTX
4
EXAMPLES
LUNG CANCER IS CAUSED BY A
CONSTELLATION OF CAUSES LIKE
•
•
•
•
SMOKING
UNFILTERED CIGARETTES
10 YEARS DURATION
AND HOST SUSCEPTIBILITY
TISSUE INSULT DUE TO
CHRONIC IRRITATION
•
Chronic irritation of any tissue may
lead to disease
1. MARJOLIN’S 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 ( Marjolin’s ulcers) in
barbers
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
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
DISEASE INITIATION
THE DISEASE IS INITITED
AT THE CELLULAR LEVEL
WHEN THE NECESSARY CAUSE
(AGENT) BECOMES SUFFICIENT
I.E. COMPLIMENTED BY ITS
CAUSAL PARTNERS
HOW IT PROGRESSES?
• Natural history of disease
Disease
initiation at
Cellular level
Carrier
State
Incubation
Period/Generatio
n time
Death
Prepathogenic
period
Pathogenic
period
Convalescent
period
HOW THE DISEASE IS
TRANSMITTED?
RESERVOIR/
SOURCE OF
AGENT
MODE OF TRANSMISSION
THROUGH SOME VEHICLE
OR VECTOR
Susceptible
Host/Non –
Immune/
Poor herd
immunity
DISEASE DISTRIBUTION
TIME DISTRIBUTION OF THE DISEASE
1.
2.
3.
4.
SHORT TERM FLUCTUATIONS,
LONG TERM FLUCTUATIONS,
PERIODIC FLUCTUATIONS,
CYCLICAL, SEASONAL,
SECULAR TRENDS
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.
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 NON–
INFECTIOUS ONES TO BE
REPLACED LATER
BY PERSONAL AND
BEHAVIORAL PROBLEMS.
•
DISEASE PREVENTION
1. PRIMORDIAL PREVENTION-INTERVENTIONS TAKEN BEFORE THE
DEVELOPMENT OF RISK FACTOR
2. PRIMARY PREVENTION -INTERVENTIONS TAKEN BEFORE THE
DISEASE IS ESTABLISHED
3. SECONDARY PREVENTION-INTERVENTIONS TAKEN AFTER THE
DISEASE IS ESTABLISHED4. TERTIARY PREVENTION -INTERVENTIONS TAKEN TO PREVENT
COMPLICATIONS
DISEASE SURVEILLANCE
• WATCHING THE DISEASE WITH
SUSPICION, ATTENTION AND
AUTHORITY
1. SUSPECT UNLESS AND UNTIL IT IS
DISPROVED
2. BE ATTENTIVE AND CAUTIOUS
3. TRY TO GRASP THE ENTIRE
NATURAL HISTORY OF THE DISEASE
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
1. CONTROL
2. ELIMINATION
3. ERADICATION
DISEASE CONTROL
• CONTROL STRATEGY = REDUCING
THE MORBIDITY AND MORTALITY
• A CONTINGENCY TEMPORARY
MEASURE IN CASE OF EMERGENCY
DISEASE ELIMINATION
• NEAR ERADICATION STAGE
• INTERMEDIARY BETWEEN CONTROL
AND ERADICATION STATUS
• LESS PUBLIC HEALTH PROBLEM
• BASED MAINLY ON SURVEILLANCE
ACTIVITIES
ERADICATION
• RADICLE MEANS MAIN ROOT OF
A PLANT
• ERADICATION MEANS REMOVING
ALONG WITH THE MAIN ROOT
i.e. IN ENTIRETY
• ALL OR NONE FORMULA
DISEASE ERADICATION
AGEENT IN
MODE OF TRANSMISSION
SUSCEPTIBLE
RESERVOIROR
POPULATION
SOURCE
TO ERADICATE THE DISEASE ONE MUST:
- ELIMINATE THE RESERVOIR/SOURCE
OF THE AGENT
- CUT OFF THE TRANSMISSION
- MAKE THE PEOPLE IMMUNE TO THAT
DISEASE
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