1. DISEASE EPIDEMIOLOGY avasarala@yahoo.com Dr . A.K.AVASARALA MBBS, M.D.
PROFESSOR & HEAD
DEPT OF COMMUNITY MEDICINE & EPIDEMIOLOGY
PRATHIMA INSTITUTE OF MEDICAL SCIENCES, KARIMNAGAR, A.P..
INDIA:
Author profile :-After medical graduation, worked for 17 years in the field as primary care physician in primary health centres, area hospitals, mobile medical units, cholera combat team, filarial control project, casualty department, divisional secondary care hospitals
Then completed post graduation in public health medicine/preventive &social medicine &epidemiology and teaching medical graduates and post graduates, nursing students, physiotherapy students, primary care personnel for the last 15 years.
At present working as Professor & Head of the department of Community medicine & Epidemiology since 15 years and practicing and contributing to the cause of epidemiological spread and growth in India (life ambition) as Indian super course epidemiology developer.
Other EIGHT super course lectures of mine can be accessed at

2. 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)
WE THINK WE KNOW EVERY THING ABOUT DISEASE DYNAMICSBUT STILL THERE ARE GAPS.
ARE THEY GAPS IN OUR UNDERSTANDING OR IN REALITY?
THIS ACTUALLY PROMPTED ME EXPRESS MY DOUBTS AND TO DEVELOP THIS LECTURE
SECONDLY, I WISH TO GIVE A GROSS PICTURE ABOUT THE DISEASE TO THE STUDENT DISCUSSING THE PRESENT REALITIES.

3. LEARNING OBJECTIVES WHAT IS DISEASE?
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?

4. 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
CONTEXTS TO UTILIZE SIX HONEST SERVINGMEN WHILE PREPARING LESSON PLAN ON ANY TOPIC
WHAT =DEFINITION
WHY= PUBLIC HEALTH SIGNIFICANCE(MAGNITUDE)
HOW=PROCESS
WHEN= TIME TRENDS
WHERE= PLACE DISTRIBUION
WHOM=PERSONS USUALLY AFFECTED

5. 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?
IS IT AN AFTER-EFFECT OF A GERM’S EFFORT TO MAINTAIN ITS OWN RACE BY MULTIPLYING AND SURVIVING AS A PARASITE IN MAN?
IS IT A DISTURBED MAN’S INTERNAL AND EXTERNAL ENVIRONMENT DUE NEGATIVE LIFE STYLES?
IS IT THE DESTINED EFFECT ACQUIRED FROM THE FOREFATHERS?
IS IT A GENE AND ENVIRONMENTAL INTERACTION?
ALL ARE TRUE TO SOME EXTENT BUT NONE IS THE COMPLETE ANSWER. THIS SHOWS THAT DISEASE HAS GOT AS MANY FACES AS GOD AND VERY DIFFICULT TO DEFINE.

6. DISEASE CAN BE SIMPLY EXPLAINED AS DIS AT EASE OR ILL HEALTH
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.
IT IS ALSO DESCRIBED AS OPPOSITE OF HEALTH WHEREIN SOME PART OR ORGAN OF THE HUMAN BEING IS DISTURBED OR AFFECTED AT SOME LEVEL, FROM CELLULAR TO ORGAN OR FUNCTIONAL LEVEL.
SOME THINK LIBERALLY THAT SICKNESS, IMPAIRMENT, DISABILITY AND HANDICAP ARE SYNONYMOUS WITH THE DISEASE.
USUALLY IMPAIRMENT IS CONSIDERED AS LOSS OF ANATOMICAL PART OF THE BODY, DISABILITY AS FUNCTIONAL LOSS, HANDICAP AS A SOCIAL LOSS AND SICKNESS AS A SOCIAL ROLE PLAYED DUE TO ILLNESS. ALL THESE ARE THE CONSEQUENCES OR EFFECTS OF A DISEASE.

7. HOW THE DISEASE IS CAUSED?
SUPERNATURAL THEORY OF DISEASE
ECOLOGICAL THEORY
GERM THEORY
MULTIFACTORIAL CAUSATION THEORY

8. 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
VERY FEW PEOPLE KNOW AND ACCEPT THAT IT IS DUE TO THEIR OWN NEGATIVE LIFE STYLES (FAULTS)
SCIENTIFIC PEOPLE BELIEVE IN ALL , INCLUDING SUPERNATURAL ORIGIN AS THEY CANNOT EXCLUDE IT AS A CAUSE OF THE DISEASE.
ARE THE CONCEPTS OF ORIGIN OF THE DISEASE REALLY CHANGING OR MIXING ?

9. 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.
BOTH THESE BELIEFS ARE PERPETUATED BY IGNORANCE, ILLITERACY AND POVERTY PREVALENT NOT ONLY IN THOSE TIMES BUT ALSO IN THE PRESENT DAYS
.THIS SUPERNATURAL ORIGIN OF THE DISEASE TOOK SUCH A STRONG ROOTS IN THE PEOPLES’ MINDS MAKING THE CONTROL AND ERADICATION OF ANY DISEASE DIFFICULT EVEN TODAY AS IT IS POTENTIALLY INFLUENCED BY THE INDIVIDUAL ‘S PERSONAL BELIEFS AND ATTITUDE.

10. ECOLOGICAL THEORY
AROUND 463 BC, HIPPOCRATES IS THE FIRST EPIDEMIOLOGIST WHO ADVISED TO SEARCH THE ENVIRONMENT FOR THE CAUSE OF THE DISEASE.
These human ecological concepts, i.e. the study of human relationship with environment made the later thinkers search the cause in environment. His advice in his treatise on “Airs, Waters and Places” elucidates vividly the role of environmental influences upon and relationships with human being in causing the disease.
HE RIGHTLY ADVISED TO SEARCH AIR, WATER AND PLACES FOR THE CAUSE OF A DISEASE.
It is the first scientific approach or reasoning regarding disease causation.
He loaded the gun of scientific thinking about disease causation while Pasteur, Henle, Koch and Pettenkoffer pulled the trigger.

11. 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.

12. 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
SELF –ELIMINATION OF THE DISEASE
BEING WELL-FED, BETTER HOUSED, WELL-INFORMED, AND SEPARATED FROM OTHERS BY ENOUGH SPACE TO REDUCE THE PROBABILITY OF PERSON-TO-PERSON TRANSMISSION OF INFECTION, ALL HELPED TO REDUCE THE BURDEN OF PREMATURE DEATH.

13. 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

14. 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.
These postulates are rigid and strongly confirm one-one theory, i.e. unifactorial causation of the disease. Though these are true to some extent for infectious diseases, they cannot explain the etiology of all diseases, particularly non-infectious diseases.
Moreover it was found that a single cause can cause several diseases and several causes can cause a single disease refuting 1-1 relationship even with infectious diseases.
. Germ cannot be found in certain diseases, particularly, non-communicable diseases further contradicting the postulates.
Sometimes, disease is found even in the absence of a germ and vice versa e.g. sputum negative tuberculosis

15. 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 TOOK A RIDE ON THE UNIFACTORIAL THEORY STATING THAT KOCH’S POSTULATES CANNOT EXPLAIN THE NON COMMUNICABLE DISEASE CAUSATION WHERE ONE CANNOT FIND A GERM.
HE GAVE GENERALIZED EXPLANATION APPLICABLE TO ALL DISEASES, INFECTIOUS AND NON-INFECTIOUS AS WELL THAT DISEASE IS MULTIFACTORIAL.
PETTENKOFFER CONTRADICTED THE UNIFACTORIAL THEORY OF DISEASE CAUSATION AND EMPHASIZED THAT DISEASE IS MULTIFACTORIAL IN CAUSATION. SEVERAL CAUSES OR FACTORS ACTING JOINTLY, CUMULATIVELY, BY COMPLEMENTING OR IN AN UNEXPLAINED MANNER WILL LEAD TO THE DISEASE.
THIS THEORY OF WEB OF CAUSATION EXPLAINS BOTH THE INFECTIOUS AND NON-INFECTIOUS DISEASES. THESE MULTIPLE CAUSES WORK THROUGH DIFFERENT GROUPS OR CONSTELLATIONS.
PETTENKOFFER

16. 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
FOR A PLANT TO GROW, SEED MUST BE PLANTED IN A FERTILE SOIL AND SHOULD BE NOURISHED WITH WATER.
SIMILARLY, THE DISEASE OCCURS ONLY WHEN THE AGENT (SEED) FINDS A SUSCEPTIBLE HOST (FERTILE SOIL) AND FAVORABLE ENVIRONMENT (SHOWER) FOR INTERACTION.
Environmental factors
(SHOWER)
Host factors (SOIL)

17. CAUSAL CONSTELLATIONS
disease
Actually, several causes form into groups or constellations to cause the disease.
A necessary or principal cause will be helped and complemented by other causes (predisposing, enabling, precipitating, reinforcing causes) making it sufficient to initiate the disease. Unless a necessary cause has enough support by other causes by means of their complementing and synergistic action, that cause can never become sufficient enough for disease initiation.
These causal partners will not loose their identity and individuality while complementing necessary cause but just help the necessary cause. While doing so, these causal partners form a web of cumulative and synergistic action with the necessary cause to initiate the disease.
That means when a necessary cause is fully complemented with its causal partners, it becomes sufficient enough to cause the disease.
Presence of a sufficient cause means that disease is initiated. This explanation is true serves for both the infectious and non-infectious 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
A = NECESSARY CAUSE
B TO X = CAUSAL PARTNERS

18. EXAMPLES LUNG CANCER IS CAUSED BY A CONSTELLATION OF CAUSES LIKE
SMOKING
UNFILTERED CIGARETTES
10 YEARS DURATION
AND HOST SUSCEPTIBILITY
Putting on a switch, though appears to be apparent single cause resulting in lighting, it is actually the result of a group or constellation of causes, which includes
wiring,
electricity,
unspent bulb
along with the switch.

19. TISSUE INSULT DUE TO CHRONIC IRRITATION
Chronic irritation of any tissue may lead to disease
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
Cancer cervix is more seen in multiparous women and less seen in nullipara. This may be due to chronic irritation due to sexual life for longer duration in multipara.
Cancer lip is more seen with chronic smokers due to chronic irritation of the delicate lip mucosa, leading to purposeless neoplastic growth
Cancer stomach is more seen with those people who insult their gastric mucosa with offending agents like drugs, hot and spicy foods, alcohol etc.
Cancer larynx is frequently seen with singers and teachers. who abuse their voices.
Personal experience. – My own maternal uncle, who developed a habit of folding and twisting the skin on his Adam’ s apple for 40 years developed epitheilioma of skin there and died.
Hence God given tissue should be respected because that greatest engineer has included in each cell , all the necessary ingredients of life.

20. 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
In India, sciences of astronomy and astrology are 5000 years old. They describe the various affects of the planetary relationships on the health of the people.
Planetary movements cause seasons of the year. They explain also the seasonal effects on health of the people.
If there is no truth in it how can they survive for centuries? This origin of the disease , we have to diligently search.

21. 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

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

23. HOW IT PROGRESSES? Natural history of disease Pre-pathogenic
period
Disease initiation at
Cellular level
Incubation
Period/Generation time
Carrier
State
Natural history of the disease is that course, the disease takes, if it is left on its own , without any interference or intervention either of preventive, promotive , curative, medical or surgical nature.
A disease when it is left like that (very rare) either ends in recovery or death. It follows usually this course as shown in the slide
Death
Pathogenic
period
Convalescent
period

24. HOW THE DISEASE IS TRANSMITTED?
Susceptible
Host/Non –
Immune/
Poor herd immunity
MODE OF TRANSMISSION THROUGH SOME VEHICLE OR VECTOR
RESERVOIR/
SOURCE OF
AGENT
Disease transmission depends upon several factors of agent (virulence, critical density, antigenicity) host (immiunity, age, personal habits) environment (herd immunity, sanitation staus, socio economic status, climate etc.)

25. DISEASE DISTRIBUTION SHORT TERM FLUCTUATIONS, LONG TERM FLUCTUATIONS,
TIME DISTRIBUTION OF THE DISEASE
SHORT TERM FLUCTUATIONS,
LONG TERM FLUCTUATIONS,
PERIODIC FLUCTUATIONS,
CYCLICAL, SEASONAL, SECULAR TRENDS
PLACE DISTRIBUTION:-
INTERNATIONAL LEVEL
NATIONAL LEVEL
REGIONAL LEVEL
LOCAL LEVEL
PERSON DISTRIBUTION OF THE DISEASE:-
AGE WISE, SEX WISE,
ACCORDING TO OCCUPATION,LITERACY, IMMUNITY, RACE, ETHNICITY, MARIIED LIFE, PERSONAL BEHAVIOUR

26. 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.
JOHN SNOW DETECTED CLUSTERING OF CHOLERA CASES AT BROAD STREET IN LONDON AND THIS CLUSTERING PROMPTED HIM NOT ONLY TO CONDUCT HIS EXPERIMENT BUT ALSO TO REMOVE THE HAD OF THE STREET PUMP TO PREVENT EPIDEMIC.

27. 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.
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.

28. 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
AT EVERY LEVEL, PREVENTION CAN BE TRIED AND SHOULD BE TRIED.
EVEN BEFORE DEATH, SOME THING CAN BE TRIED TO MITIGATE THE SUFFERING.
PHILOSOPHY OF PREVENTION IS THE CORNERSTONE WHILE DEALING WITH PATIENTS IN HOSPITAL SETTING OR IN POPULATION

29. DISEASE SURVEILLANCE METHODS:-
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
KEEPING TRACK OF TRENDS AND EVENTS OF THE DISEASE.
METHODS:-
LAYMAN REPORTING
ACTIVE SURVEILLANCE
PASSIVE SURVEILLANCE
SENTINEL SURVEILLANCE
SERO SURVEILLANCE

30. 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

31. DISEASE CONTROL
CONTROL STRATEGY = REDUCING THE MORBIDITY AND MORTALITY
A CONTINGENCY TEMPORARY MEASURE IN CASE OF EMERGENCY
SOURCE S/ RESERVOIRS WITH VIRULENT AGENT ARE IN ABUNDANCE
TRANSMISSION IS HIGH
POPULATION WITH PLENTY OF SUSCEPTIBILES
Methods of control :-
Notification
Isolation
Quarantine
Surveillance
Chemotherapy
Prophylaxis

32. DISEASE ELIMINATION NEAR ERADICATION STAGE
INTERMEDIARY BETWEEN CONTROL AND ERADICATION STATUS
LESS PUBLIC HEALTH PROBLEM
BASED MAINLY ON SURVEILLANCE ACTIVITIES
LESS NUMBER OF SOURCES
AGENT IS STLL PRESENT BUT LESS VIRULENT
TRANSMISSION IS PRESENT BUT AT LOW EBB
SUSCEPTIBLES STILL PRESENT

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

34. DISEASE ERADICATION TO ERADICATE THE DISEASE ONE MUST:
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
AGENT PERISHED IN POPULATION
NO TRANSMISSION
NO SUSCEPTIBLES IN POPULATIONS . (IMMUNE POPULATIONS)
HENCE NO DISEASE

35. 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
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