CONCEPTS OF CONCEPTS OF DISEASE DISEASE

CAUSATIONCAUSATION

DR MIRZA INAMUL HAQ DR MIRZA INAMUL HAQ

AP COMMUNITY MEDICINEAP COMMUNITY MEDICINE

LEARNING OBJECTIVESLEARNING OBJECTIVES

The student should learn disease The student should learn disease processprocess

•What are the theories of What are the theories of causation of disease?causation of disease?

•How is it transmitted? How it How is it transmitted? How it spreads? spreads?

•How it is distributed? And why?How it is distributed? And why?•How it can be prevented and its How it can be prevented and its

importance in public health ?importance in public health ?

WHAT EXACTLY IS A WHAT EXACTLY IS A DISEASE IS STILL A ?DISEASE IS STILL A ?

• IS IT A SEQUENCE OF IS IT A SEQUENCE OF PATHOLOGICAL CHANGES AND PATHOLOGICAL CHANGES AND THEIR EFFECTS OCCURRING IN THEIR EFFECTS OCCURRING IN THE INDIVIDUAL?THE INDIVIDUAL?

• IS IT A COMPOSITE OF EFFECTS IS IT A COMPOSITE OF EFFECTS DUE TO DISTURBANCE IN MAN’S DUE TO DISTURBANCE IN MAN’S RELATIONSHIP WITH HIS RELATIONSHIP WITH HIS ENVIRONMENT BY AN ENVIRONMENT BY AN AGENT/FACTOR?AGENT/FACTOR?

WHAT IS A WHAT IS A DISEASEDISEASE??

DISEASE CAN BE SIMPLY DISEASE CAN BE SIMPLY EXPLAINEDEXPLAINED

AS AS DISDIS AT AT EASEEASE OR ILL HEALTHOR ILL HEALTH

SOME DESCRIBE IT AS SOME DESCRIBE IT AS DISTURBANCE IN DISTURBANCE IN

EQUILIBRIUM BETWEEN EQUILIBRIUM BETWEEN MAN AND HIS TOTAL MAN AND HIS TOTAL

ENVIRONMENT.ENVIRONMENT.

HOW THE DISEASE IS HOW THE DISEASE IS CAUSED?CAUSED?

1.1. SUPERNATURAL THEORY SUPERNATURAL THEORY OF DISEASEOF DISEASE

2.2. ECOLOGICAL THEORY ECOLOGICAL THEORY

3.3. GERM THEORY GERM THEORY

4.4. MULTIFACTORIAL MULTIFACTORIAL CAUSATION THEORYCAUSATION THEORY

NO UNANIMOUS OPINIONNO UNANIMOUS OPINION• AT LEAST 10% OF THE PEOPLE IN DEVELOPED AT LEAST 10% OF THE PEOPLE IN DEVELOPED

COUNTRIES AND 30% IN DEVELOPING COUNTRIES AND 30% IN DEVELOPING COUNTRIES STILL BELIEVE IN SUPERNATURAL COUNTRIES STILL BELIEVE IN SUPERNATURAL ORIGINORIGIN

• EVEN TODAY SUPERSTITIONS ARE BECOMING EVEN TODAY SUPERSTITIONS ARE BECOMING MAJOR OBSTACLES IN DISEASE CONTROLMAJOR OBSTACLES IN DISEASE CONTROL

• MOST OF THE LITERATES VIEW THAT DISEASE IS MOST OF THE LITERATES VIEW THAT DISEASE IS THE RESULT OF MICROBES THE RESULT OF MICROBES

• MOST OF THE UNEDUCATED PEOPLE (90%) MOST OF THE UNEDUCATED PEOPLE (90%) BELIEVE THAT DISEASE IS DUE TO BAD BELIEVE THAT DISEASE IS DUE TO BAD PHYSICAL ENVIRONMENT PHYSICAL ENVIRONMENT

SUPERNATURAL THEORY OF SUPERNATURAL THEORY OF DISEASEDISEASE::

• IN THE EARLY PAST, THE DISEASE IN THE EARLY PAST, THE DISEASE WAS THOUGHT MAINLY DUE TO WAS THOUGHT MAINLY DUE TO EITHER THE CURSE OF GOD OR EITHER THE CURSE OF GOD OR DUE TO THE EVIL FORCE OF THE DUE TO THE EVIL FORCE OF THE DEMONS. ACCORDINGLY, PEOPLE DEMONS. ACCORDINGLY, PEOPLE USED TO PLEASE THE GODS BY USED TO PLEASE THE GODS BY PRAYERS AND OFFERINGS OR PRAYERS AND OFFERINGS OR USED TO RESORT TO USED TO RESORT TO WITCHCRAFT TO TAME THE WITCHCRAFT TO TAME THE DEVILS.DEVILS.

ECOLOGICAL THEORYECOLOGICAL THEORY

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

ENVIRONMENTAL ENVIRONMENTAL INFLUENCEINFLUENCE

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

ECOLOGICAL ECOLOGICAL DETERMINANTS OF DISEASEDETERMINANTS OF DISEASE

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

PLANETS AND DISEASEPLANETS AND DISEASE

• IT IS WELL KNOWN THAT PLANETS IT IS WELL KNOWN THAT PLANETS (EARTH,SUN, MOON ) AND THEIR (EARTH,SUN, MOON ) AND THEIR MOVEMENTS, THEIR INTER MOVEMENTS, THEIR INTER DISTANCES AND RELATIONSHIPS DISTANCES AND RELATIONSHIPS WILL CAUSE SEASONS OF THE YEARWILL CAUSE SEASONS OF THE YEAR

• PLANETS’ INFLUENCE ON ORIGIN PLANETS’ INFLUENCE ON ORIGIN OF SEASONAL DISEASES AND THEIR OF SEASONAL DISEASES AND THEIR CONTROL IS STILL A PANDORA BOXCONTROL IS STILL A PANDORA BOX

GERM THEORYGERM THEORY

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

ROBERT KOCH

HENLE-KOCH POSTULATESHENLE-KOCH POSTULATES

Henle and Koch have postulated that Henle and Koch have postulated that

1.1.Each disease will be caused by a germEach disease will be caused by a germ

2.2.Without that germ that disease will not Without that germ that disease will not be causedbe caused

3.3.By introducing that germ , that disease By introducing that germ , that disease can be caused in animals experimentally,can be caused in animals experimentally,

4.4.And that germ can again be isolated from And that germ can again be isolated from that sick animal experimented with. that sick animal experimented with.

MULTIFACTORIAL MULTIFACTORIAL CAUSATION THEORYCAUSATION THEORY

• PETTENKOFFERPETTENKOFFER

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

WHEN THE DISEASE WHEN THE DISEASE OCCURS?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 CONSTELLATIONSCAUSAL 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

EXAMPLESEXAMPLES

LUNG CANCER IS CAUSED BY A LUNG CANCER IS CAUSED BY A CONSTELLATION OF CAUSES LIKECONSTELLATION OF CAUSES LIKE

• SMOKING SMOKING • UNFILTERED CIGARETTESUNFILTERED CIGARETTES• 10 YEARS DURATION 10 YEARS DURATION • AND HOST SUSCEPTIBILITY AND HOST SUSCEPTIBILITY

INCUBATIONINCUBATION

• THE AGENT INCUBATES TO THE AGENT INCUBATES TO ACQUIRE THE CRITICAL ACQUIRE THE CRITICAL DENSITY TO INITIATE THE DENSITY TO INITIATE THE DISEASE DISEASE

• IT MULTIPLIES OR INCREASES IT MULTIPLIES OR INCREASES IN INTENSITY FOR A SPECIFIC IN INTENSITY FOR A SPECIFIC PERIOD BEFORE BECOMING PERIOD BEFORE BECOMING OVERT AND CLINICALOVERT AND CLINICAL

DISEASE INITIATIONDISEASE INITIATION

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

HOW IT PROGRESSES?HOW IT PROGRESSES?

• Natural history of diseaseNatural history of disease

CarrierState

Incubation Period/Generation time

Pre-pathogenic period

Pathogenic period

Convalescentperiod

Disease initiation atCellular level

Death

HOW THE DISEASE IS HOW THE DISEASE IS TRANSMITTED?TRANSMITTED?

RESERVOIR/SOURCE OF AGENT

MODE OF TRANSMISSION THROUGH SOME VEHICLE OR VECTOR

SusceptibleHost/Non –Immune/Poor herd immunity

DISEASE DISTRIBUTIONDISEASE DISTRIBUTION

TIME DISTRIBUTION OF THE TIME DISTRIBUTION OF THE DISEASEDISEASE

1.1. SHORT TERM FLUCTUATIONS, SHORT TERM FLUCTUATIONS, 2.2. LONG TERM FLUCTUATIONS,LONG TERM FLUCTUATIONS,3.3. PERIODIC FLUCTUATIONS, PERIODIC FLUCTUATIONS, 4.4. CYCLICAL, SEASONAL, CYCLICAL, SEASONAL,

SECULAR TRENDSSECULAR TRENDS

DISEASE PREVENTIONDISEASE PREVENTION1.1. PRIMORDIAL PREVENTION-PRIMORDIAL PREVENTION-- -

INTERVENTIONS TAKEN BEFORE THE INTERVENTIONS TAKEN BEFORE THE DEVELOPMENT OF RISK FACTORDEVELOPMENT OF RISK FACTOR

2.2. PRIMARY PREVENTIONPRIMARY PREVENTION -- -- INTERVENTIONS TAKEN BEFORE THE INTERVENTIONS TAKEN BEFORE THE DISEASE IS ESTABLISHEDDISEASE IS ESTABLISHED

3.3. SECONDARY PREVENTION-SECONDARY PREVENTION-- - INTERVENTIONS TAKEN AFTER THE INTERVENTIONS TAKEN AFTER THE DISEASE IS ESTABLISHED-DISEASE IS ESTABLISHED-

4.4. TERTIARY PREVENTIONTERTIARY PREVENTION -- -- INTERVENTIONS TAKEN TO PREVENT INTERVENTIONS TAKEN TO PREVENT

COMPLICATIONS COMPLICATIONS

PUBLIC HEALTH PUBLIC HEALTH PROBLEMPROBLEM

• DISEASE WILL BE A PUBLIC HEALTH DISEASE WILL BE A PUBLIC HEALTH PROBLEM WHEN IT CAUSES HIGH PROBLEM WHEN IT CAUSES HIGH MORBIDITY AND MORTASLITYMORBIDITY AND MORTASLITY

• DEMANDS URGENT HEALTH ACTIONDEMANDS URGENT HEALTH ACTION

EITHER IN THE FORM OF EITHER IN THE FORM OF

1.1. CONTROLCONTROL

2.2. ELIMINATIONELIMINATION

3.3. ERADICATIONERADICATION