DISEASE EPIDEMIOLOGY

1. 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@yahoo.com

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)

3. 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?

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

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?

6. WHAT IS A DISEASE? DISEASE CAN BE SIMPLY EXPLAINED AS DISAT EASEOR ILL HEALTH SOME DESCRIBE IT AS DISTURBANCE IN EQUILIBRIUM BETWEEN MAN AND HIS TOTAL ENVIRONMENT.

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

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.

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

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

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.

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

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 Environmental factors (SHOWER) Host factors (SOIL)

17. 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

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

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

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

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 Incubation Period/Generation time Disease initiation at Cellular level Carrier State Pathogenic period Death 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

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

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.

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.

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

29. 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

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

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

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 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

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 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