DISEASE EPIDEMIOLOGY

Dr . A.K.AVASARALA MBBS, M.D.PROFESSOR & HEADDEPT OF COMMUNITY MEDICINE & EPIDEMIOLOGYPRATHIMA INSTITUTE OF MEDICAL SCIENCES, KARIMNAGAR, A.P..INDIA: +91505417avasarala@yahoo.com

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 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 EXPLAINEDAS 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

• 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

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

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

PETTENKOFFER

WHEN THE DISEASE OCCURS?

DISEASE OCCURS ONLY WHEN THE HOST FACTORS AND ENVIRONMENTAL FACTORS MAKE THE AGENT SUFFICIENT ENOUGH TO CAUSE THE DISEASE

D

Agent (SEED) factors

Host factors (SOIL)

Environmental factors(SHOWER)

CAUSAL CONSTELLATIONS

disease

Causal constellations 1 2 3 4

A B C D E A F G H J K A L M N P Q A R S T X

A = NECESSARY CAUSEB TO X = CAUSAL PARTNERS

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

CarrierState

Incubation Period/Generation time

Pre-pathogenic period

Pathogenic period

Convalescentperiod

Disease initiation atCellular level

Death

HOW THE DISEASE IS TRANSMITTED?

RESERVOIR/SOURCE OF AGENT

MODE OF TRANSMISSION THROUGH SOME VEHICLE OR VECTOR

SusceptibleHost/Non –Immune/Poor herd immunity

DISEASE DISTRIBUTION

TIME DISTRIBUTION OF THE DISEASE

1. SHORT TERM FLUCTUATIONS, 2. LONG TERM FLUCTUATIONS,3. PERIODIC FLUCTUATIONS, 4. 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 PREVENTION1. 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 ESTABLISHED-

4. 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 RESERVOIROR SOURCE

SUSCEPTIBLEPOPULATION

MODE OF TRANSMISSION

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