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Epidemiology

Epidemiology. Patterns of Microbe-Human Interactions in Causing Infection and Disease. The Human Host. Contact, Infection, Disease- A Continuum Body surfaces are constantly exposed to microbes

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Epidemiology

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  1. Epidemiology Patterns of Microbe-Human Interactions in Causing Infection and Disease

  2. The Human Host • Contact, Infection, Disease- A Continuum • Body surfaces are constantly exposed to microbes • Inevitably leads to infection: pathogenic microorganisms penetrate the host defenses, enter the tissues, and multiply • Pathologic state that results when the infection damages or disrupts tissues and organs- disease • Infectious disease: the disruption of a tissue or organ caused by microbes or their products

  3. The Nature of Infectious Disease • Infection is the invasion of the host by a pathogen • Disease results only if the invading pathogen alters the normal functions of the body • Disease is also referred to as morbidity

  4. Classification of Infectious Disease • Diseases can be classified in number of ways • The taxonomic groups of the causative agent • The body system they affect • Their longevity and severity • How they are spread to their host • The effects they have on populations (rather than on individuals)

  5. Epidemiology The study of epidemics. The study of distribution and prevalence of infectious disease in a given population. The study of comparisons of baseline infections to cases. Interested in protecting the public from outbreaks of infection.

  6. Who, When, and Where? Tracking Disease in the Population • Epidemiologists concerned with virulence, portals of entry and exit, and the course of the disease • Also interested in surveillance: collecting, analyzing, and reporting data on the rates of occurrence, mortality, morbidity, and transmission of infections • Reportable diseases: by law, must be reported to authorities • Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia • Weekly notice: the Morbidity and Mortality Report • Shares statistics with the World Health Organization (WHO)

  7. Epidemiology All outbreaks follow a pattern. If we can understand the pattern, then we can intervene to prevent further cases.

  8. Epidemic Short term increase in a given infectious disease in a give population.

  9. Endemic Presence of infectious disease in a given population or in a given geographical location all the time. Ebola in Africa Lyme disease in Texas Rabies in Austin (bats)

  10. Pandemic Worldwide or global increase in an infectious disease over a long period of time. HIV/AIDS Tuberculosis

  11. Figure 13.16

  12. Epidemiology Terms Morbidity – number of cases of specific infectious disease in a give population at any given time. Mortality – number of deaths from a specific infectious disease in a given population at any given time.

  13. Epidemiology Terms Prevalence – number of cases at any give time (people are either getting better or becoming infected.) Incidence – number of new cases of a specific infectious disease. This is important because it can tell us how fast the disease is spreading.

  14. Frequency of Disease • Track occurrence of diseases using two measures • Incidence – number of new cases of a disease in a given area during a given period of time • Prevalence – number of total cases of a disease in a given area during a given period of time • Occurrence also evaluated in terms of frequency and geographic distribution

  15. Epidemiology of Infectious Diseases [INSERT FIGURE 14.17]

  16. Causation of Disease: Etiology • Exceptions to Koch’s postulates • Using Koch’s postulates is not feasible in all cases • Some pathogens can’t be cultured in the laboratory • Some diseases are caused by a combination of pathogens and other cofactors • Ethical considerations prevent applying Koch’s postulates to pathogens that require a human host • Difficulties in satisfying Koch’s postulates • Diseases that can be caused by more than one pathogen • Pathogens that are ignored as potential causes of disease

  17. Epidemiology Application Epidemiologists work to figure out what is going on so they can intervene. Every infectious disease has a pattern (not random.) Epidemiologists want to know: Place People Time

  18. The Stages of Infectious Disease • Following infection, a sequence of events called the diseaseprocess occurs • Many infectious diseases have five stages following infection • Incubation period • Prodromal period • Illness • Decline • Convalescence

  19. . Exposure – Preclinical symptoms – before you go to the doctor. You may not realize that you have an infectious agent, but your body has begun to have immune response. A preclinical symptom can be any cytopathic effect. Clinical symptoms – symptoms that can be appreciated. In TB clinical symptoms could include: cough, blood in phlegm, fever, night sweats. Incubation period – spans from exposure to the time when clinical symptoms are detected. Intervention – this is period when people seek medical attention. Options during intervention include: quarantine and medicate individuals that were exposed or vaccination. Outcome – possible outcomes: Get better (convalesce) Death Impairments (mental and physical)

  20. Epidemiological Studies • Descriptive epidemiology • Careful tabulation of data concerning a disease • Record information about the location and time of the cases of disease • Collect patient information • Try to identify the index case (or first case) of the disease

  21. Epidemiological Studies • Analytical epidemiology • Seeks to determine the probable cause, mode of transmission, and methods of prevention • Useful in situations in which Koch’s postulates can’t be applied • Often retrospective – investigation occurs after an outbreak has occurred

  22. Epidemiological Studies • Experimental epidemiology • Involves testing a hypothesis concerning the cause of a disease • Application of Koch’s postulates is experimental epidemiology

  23. Modes of Infectious Disease Transmission • Transmission is either from a reservoir or a portal of exit to another host’s portal of entry • Three groups of transmission • Contact transmission • Direct, indirect, or droplet • Vehicle transmission • Airborne, waterborne, or foodborne • Vector transmission • Biological or mechanical

  24. The Movement of Pathogens Out of Hosts: Portals of Exit • Pathogens leave host through portals of exit • Many portals of exit are the same as portals of entry • Pathogens often leave hosts in materials the body secretes or excretes

  25. The Acquisition and Transmission of Infectious Agents • Communicable disease: when an infected host can transmit the infectious agent to another host and establish infection in that host • Transmission can be direct or indirect • Contagious agent: highly communicable • Noncommunicable disease: does not arise through transmission of the infectious agent from host to host • Acquired through some other, special circumstance • Compromised person invaded by his or her own microbiota • Individual has accidental contact with a microbe in a nonliving reservoir

  26. Transmission • Contact transmission • Indirect transmission • Vehicle: any inanimate material commonly used by humans that can transmit infectious agents (food, water, biological products, fomites) • Contaminated objects (doorknobs, telephones, etc.) • Food poisoning • Oral-fecal route • Air as a vehicle • Indoor air • Droplet nuclei • Aerosols

  27. Foods as a Modes of Infectious Disease Transmission [INSERT FIGURE 14.13]

  28. Reservoirs: Where Pathogens Persist • Reservoir: the primary habitat in the natural world from which a pathogen originates • Source: the individual or object from which an infection is actually acquired • Living Reservoirs • Carrier: an individual who inconspicuously shelters a pathogen and spreads ith to others without any notice • Asymptomatic carriers • Incubation carriers • Convalescent carriers • Chronic carrier • Passive carrier

  29. Arthropods As Sources • Vector: a live animal that transmits an infectious agent from one host to another • Majority are arthropods • Larger animals can also be vectors • Biological vector: actively participates in a pathogen’s life cycle • Mechanical vectors: transport the infectious agent without being infected

  30. Vectors [INSERT TABLE 14.10]

  31. Zoonosis • Zoonosis: an infection indigenous to animals but naturally transmissible to humans • Human does not contribute to the persistence of the microbe • Can have multihost involvement • At least 150 worldwide

  32. Nonliving Reservoirs • Human hosts in regular contact with environmental sources • Soil • Water

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