MICR 201 Microbiology for Health Related Sciences

1. Lecture 7: Principles of disease and epidemiology Edith Porter, M.D. MICR 201 Microbiology for Health Related Sciences

2. Lecture Outline • Case study (Video) • Pathology, infection, and disease • Normal microbiota • Etiology of infectious diseases • Koch’s postulates and exceptions • Classifying infectious diseases • Patterns of disease • Spread of infections • Nosocomial infections • Emerging infectious diseases • Epidemiology

3. Important Definitions (1) • Pathology • Scientific study of disease • Etiology • Study of the cause of a disease • Pathogenesis • Development of disease • Infection • Colonization of the body by microbes that are not routinely present at this site • Disease • A change from state of health • Abnormal state in which the body is not function normally Pathos = Suffering Logos = Science HIV pos.  AIDS Tuberculin pos.  Tuberculosis

4. Important Definitions (2) • Pathogen • Causes disease in a healthy adult • Expresses special virulence or pathogenicity factors • Is not part of normal flora • Opportunist • Does not cause disease under normal conditions • Causes disease at local or systemic breaches of host defense • Often part of normal flora • Cooperation • Different microbes together cause disease

5. Normal Microbiota (Normal Flora) • Body is sterile in utero • Colonized within hours after birth • Lactobacilli • Staphylococci • Outnumber body cells by at least 10– fold • Normal flora does not cause disease under normal conditions • Transientmicrobiota • present for a relatively short period of time (days, weeks, or months) • Residentmicrobiota • Normal microbiota permanently colonizing the host

6. Body sites typically populated

7. Distribution of normal microbiotain human body Low numbers of Candida albicanscan be found everywhere

8. Examples for normal microbiota Nose Stomach Intestine

9. Note: Table 14.1! Trichomonas vaginalis is considered a pathogen • Trichomonas hominis is normal flora in large intestine

10. Normal microbiota and the host Normal microbiota • Competes with potential pathogens for nutrients • Directly inhibits potential pathogens • Lactobacilli: lactic acid, low pH • Bacteriocins • Produces some vitamins (K, B)

11. Loss of normal microbiota triggers infectious diseases Candidiasis after antibiotic treatment Clostridium difficile diarrhea after antibiotic therapy http://www.health-res.com/EX/07-28-04/37FF1.jpeg

12. Pseudomembranous enterocolitis caused by C. difficile

13. Probiotics • Administration of viable bacteria to the benefit of human health • Lactobacilli, Streptococci, Bifidobacteria • Withstand HCl, bile salts • Adhere to host intestinal mucosa • Produce useful enzymes or physiological end products • Restore normal microbiota • Prophylactic application • Lactobacilli to prevent development of antibiotic associated diarrhea • Therapeutic applications • Supplementary therapy in chronic UTI with E. coli

14. The etiology of infectious diseases: Koch’s postulates Robert Koch established the “Golden Rule” to positively identify a microorganism as the cause of an infectious disease • The same pathogen must be present in every case of disease and not in the healthy one. • The pathogen must be isolated from the diseased host and grown in pure culture. • The pathogen from the pure culture must cause same disease when it is inoculated into a healthy susceptible host. • The same pathogen must be isolated from the inoculated host in pure culture.

15. Exceptions to Koch’s postulates • Microorganism cannot be grown in the laboratory in/on artificial culture media • Utilization of animals or eggs for propagation • One disease can be caused by multiple microorganisms • E. g. nephritis • One microorganism can cause multiple disease conditions

16. Tuberculosis has many faces http://2.bp.blogspot.com/_ayDfkQkrVmU/TFJ0clyjbWI/AAAAAAAAAIs/5oG7IQ7UuHI/s1600/post+mortem+Dis+alpacas.JPG http://www.path.cam.ac.uk/Abnormal/TB_Tuberculosis/TB_Tuberculosis/SN_Spine/A_TB_TB_SN_02.jpg

17. Exceptions to Koch’s postulates • Microorganism cannot be grown in the laboratory in/on artificial culture media • Utilization of animals or eggs for propagation • One disease can be caused by multiple microorganisms • E. g. nephritis • One microorganism can cause multiple disease conditions • M. tuberculosis can affect skin, lungs, bones etc. • No host other than humans • E.g. HIV • More than one microorganisms cause one infection • Polymicrobial infections such as abscess caused by anaerobic bacteria

18. Classifying infectious diseases (1) • Symptom • A change in body function that is felt by a patient as a result of disease • Sign • A change in a body that can be measured or observed as a result of disease • Syndrome • A specific group of signs and symptoms that accompany a disease Often used interchangeable

19. Classifying infectious diseases (2) • Communicable disease • A disease that is spread from one host to another • Example: Tuberculosis • Contagious disease • A disease that is easily spread from one host to another • Example: Chicken pox • Noncommunicable disease • A disease that is not transmitted from one host to another • Example: Tetanus

20. Incidence Number of people in a population who develop a disease during a particular time period Includes new cases Prevalence Number of people in a population having a specific disease at a given time Includes old a new cases Sporadic disease Disease that occurs occasionally in a population Endemic disease Disease constantly present in a population Epidemic disease Disease acquired by many hosts in a given area in a short time Pandemic disease Worldwide epidemic Occurrence of disease (1)

21. Occurrence of disease (2)

22. Severity or duration of disease • Acute disease • Symptoms develop rapidly • Chronic disease • Disease develops slowly • Subacute disease • Symptoms between acute and chronic • Latent disease • Disease with a period of no symptoms when the infectious agent is inactive • Herd immunity • Many immune people are present in a population preventing the spread of a disease Herd Immunity

23. Stages of Infectious Diseases Often contagious during incubation and prodormal period!!

24. Extent of host involvement (1) • Local infection • Pathogens limited to a small area of the body • Systemic infection • An infection spread through the body (via blood or lymphatic system) • Focal infection • Systemic infection that began as a local infection

25. Extent of host involvement (2) • Bacteremia • Bacteria in the blood • Septicemia • Spread of bacteria through the blood with organ manifestation • Toxemia • Toxins in the blood • Fungemia • Fungi in the blood • Viremia • Viruses in the blood Common cause for bacteremia: Coagulase negative staphylococci colonizing i.v. catheter

26. Predisposing factors • Factors that make the body more susceptible to disease • Primary and secondary infection • Acute infection that causes the initial illness and predisposes to a secondary, often opportunistic infection • Male versus female • Genetic background • Climate and weather • Nutrition • Lifestyle • Occupation • Pre-existing illness Example: Influenza and Haemophilusinfluenzae

27. Reservoirs of infection • Continual sources of the disease organisms • Humans — AIDS, gonorrhea • Carriers may have inapparent infections or latent diseases • Animals — Rabies, Lyme disease • Some zoonoses may be transmitted to humans • Nonliving — Botulism, tetanus • Soil Lyme Disease: Skin manifestation Tick Borreliaburgdorferi

28. Spread of disease

29. Transmission of disease through contact • Direct • Requires close association between infected and susceptible host • Includes fecal-oral • Indirect • Spread by fomites • Droplets • Transmission via airborne droplets

30. Transmission of disease through vehicle • Inanimate reservoir • Food • Water • Vectors • Arthropods • Fleas : plague • Ticks: Lyme disease • Mosquitoes: malaria • Mechanical • Biological : some part of the development of the microbe takes place in the vector

31. Nosocomial(hospital-acquired) infections • Acquired during a hospital stay • Source is hospital • 5-15 % of all hospital patients affected

32. Principle sites of nosocomial infections

33. Microorganisms involved in nosocomial infections

34. Emerging infectious diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future

35. Appearance of new strains by genetic recombination E. coli O157:H7 Avian influenzavirus H5N1 Evolution of new serovars V. cholerae O139 Inappropriate use of antibiotics and pesticides Antibiotic resistant strains Multidrug resistant M. tuberculosis Global warming and weather changes Hantavirus pulmonary syndrome Spread of known diseases by modern transportation Cholera Ecological Disaster Coccidioidomycosis after Northridge earthquake Failures in public health Missed immunizations Factors contributing to the emergence of infectious diseases

36. What is Epidemiology? • As told by CDC … • It seems that one of their scientists, on first arriving at CDC from a clinical practice, found himself somewhat unsure of what epidemiology was all about, so he sought an answer down the street at Emory University. • The first person he asked was a medical student, who told him that epidemiology was "the worst taught course in medical school." • The second, a clinical faculty member, told him epidemiology was "the science of making the obvious obscure." • Finally, knowing that statistics are important to epidemiology, he asked a statistician, who told him that epidemiology is "the science of long division" and provided him with a summary equation. Giving up on finding a real answer, he returned to CDC. • On the way, however, he decided to try one more time. He stopped a native Atlantanwho told him that epidemiology was "the study of skin diseases.”

37. What is Epidemiology really? • Discipline that find answers to When? Where? How transmitted? • Study—Epidemiology is the basic science of public health. It's a highly quantitative discipline based on principles of statistics and research methodologies. • Distribution—Epidemiologists study the distribution of frequencies and patterns of health events within groups in a population. To do this, they use descriptive epidemiology, which characterizes health events in terms of time, place, and person. • Determinants—Epidemiologists also attempt to search for causes or factors that are associated with increased risk or probability of disease. This type of epidemiology, where we move from questions of "who," "what," "where," and "when" and start trying to answer "how" and "why," is referred to as analytical epidemiology.

38. What is Epidemiology really? • Health-related states—Epidemiology as it is practiced today is applied to the whole spectrum of health-related events, which includes chronic disease, environmental problems, behavioral problems, and injuries in addition to infectious disease. • Populations—One of the most important distinguishing characteristics of epidemiology is that it deals with groups of people rather than with individual patients. • Control—Epidemiological data steers public health decision making and aids in developing and evaluating interventions to control and prevent health problems. This is the primary function of applied, or field, epidemiology.

39. Modern history of epidemiology • John Snow • Cholera outbreaks in London 1848-1849 • IgnazSemmelweis • Childbed fever (puerperal sepsis) 1846 - 1848 • Florence Nightingale • Epidemic typhus 1858

40. John Snow and cholera • Cholera epidemics in London 1846 – 1849 • Snow analyzed the death records and interviewed survivors • Created map • Most individuals who died of cholera used water from Broad street pump • Survivors did not drink water but beer instead or used another pump • Identified the Broad street water pump as likely source • After closing this pump number of cholera cases dropped significantly

41. IgnazSemmelweis and puerperal sepsis Mandatory hand washing introduced

42. Florence Nightingale and epidemic typhus • Recorded statistics on epidemic typhus in English civilian and military populations • Published a 1000 page report in 1858 • Statistically linked disease and death with poor food and unsanitary conditions • Novel graph: coxcomb chart or polar area diagram chart • Fixed angle and variable radii • Resulted in reforms in the British Army • Nightingale became the first female member of the Statistical Society

43. Investigation types in epidemiology • Experimental • Epidemiologist is in control of the circumstances at the beginning of the study • Begins with a hypothesis • Prospective study that usually involves controls • Example: Semmelweis’ study; vaccine efficacy trials • Observational (or descriptive) • Epidemiologist is not in control of the circumstances at the beginning of the study • Descriptive • Collect data about affected individuals, the places and the periods in which disease occurred (Who? Where? When?) • Typically retrospective • E.g. Snow’s study • Analytical • Analyzes a particular disease to determine its probable cause (How? Why?) • Case control method – look for factors that might have preceded the disease • Cohort method – study of two populations, one having had contact with the disease agent and the other that has not • E.g., Nightingale’s study