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Principles of Disease and Epidemiology: Understanding Pathology, Infection, and Transmission

Learn about the principles of disease, including etiology, pathogenesis, and transmission. Explore how pathogens colonize the body, the role of normal microbiota, and the classification of infectious diseases. Understand the occurrence and severity of diseases, as well as the factors that make the body more susceptible. Discover the different stages of a disease and the various reservoirs and modes of transmission. Gain knowledge on nosocomial infections and emerging infectious diseases.

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Principles of Disease and Epidemiology: Understanding Pathology, Infection, and Transmission

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  1. Chapter 14 Principles of Disease and Epidemiology

  2. Principles of Disease and Epidemiology • Pathology Study of disease • Etiology Study of the cause of a disease • Pathogenesis Development of disease • Infection Colonization of the body by pathogens • Disease An abnormal state in which the body is not functionally normally

  3. Normal Microbiota and the Host • Transient microbiota may be present for days, weeks, or months • Normal microbiota permanently colonize the host • Symbiosis is the relationship between normal microbiota and the host

  4. Normal Microbiota and the Host: • In commensalism, one organism is benefited and the other is unaffected. • In mutualism, both organisms benefit. • In parasitism, one organism is benefited at the expense of the other. • Some normal microbiota are opportunistic pathogens.

  5. Normal Microbiota and the Host: • Locations of normal microbiota on and in the human body Figure 14.2

  6. Normal Microbiota and the Host: • Microbial antagonism is competition between microbes. • Normal microbiota protect the host by: • occupying niches that pathogens might occupy • producing acids • producing bacteriocins • Probiotics are live microbes applied to or ingested into the body, intended to exert a beneficial effect.

  7. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.1

  8. Koch’s Postulates • Koch's Postulates are used to prove the cause of an infectious disease. Figure 14.3.2

  9. Classifying Infectious Diseases • 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.

  10. Classifying Infectious Diseases • Communicable disease A disease that is easily spread from one host to another. • Contagious disease A disease that is easily spread from one host to another. • Noncommunicable disease A disease that is not transmitted from one host to another.

  11. Occurrence of Disease • Incidence Fraction of a population that contracts a disease during a specific time. • Prevalence Fraction of a population having a specific disease at a given time. • 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. • Herd immunity Immunity in most of a population.

  12. Severity or Duration of a 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 patient is inactive

  13. Extent of Host Involvement • Local infection Pathogens limited to a small area of the body • Systemic infection An infection throughout the body • Focal infection Systemic infection that began as a local infection • Bacteremia Bacteria in the blood • Septicemia Growth of bacteria in the blood

  14. Extent of Host Involvement • Toxemia Toxins in the blood • Viremia Viruses in the blood • Primary infection Acute infection that causes the initial illness • Secondary infection Opportunistic infection after a primary (predisposing) infection • Subclinical disease No noticeable signs or symptoms (inapparent infection)

  15. Predisposing Factors • Make the body more susceptible to disease • Short urethra in females • Inherited traits such as the sickle-cell gene • Climate and weather • Fatigue • Age • Lifestyle • Chemotherapy

  16. The Stages of a Disease Figure 14.5

  17. Reservoirs of Infection • Reservoirs of infection are continual sources of infection. • Human — AIDS, gonorrhea • Carriers may have inapparent infections or latent diseases • Animal — Rabies, Lyme disease • Some zoonoses may be transmitted to humans • Nonliving — Botulism, tetanus • Soil

  18. Transmission of Disease • Contact • Direct Requires close association between infected and susceptible host • Indirect Spread by fomites • Droplet Transmission via airborne droplets

  19. Transmission of Disease Figure 14.6a & 8

  20. Transmission of Disease • Vehicle Transmission by an inanimate reservoir (food, water) • Vectors Arthropods, especially fleas, ticks, and mosquitoes • Mechanical Arthropod carries pathogen on feet • Biological Pathogen reproduces in vector

  21. Transmission of Disease Figure 14.6b, c

  22. Nosocomial (Hospital-Acquired) Infections • Are acquired as a result of a hospital stay • 5-15% of all hospital patients acquire nosocomial infections Figure 14.7, 9

  23. Relative frequency of nosocomial infections Figure 14.10

  24. Common Causes of Nosocomial Infections

  25. Emerging Infectious Diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. • Contributing factors: • Evolution of new strains • V. cholerae O139 • Inappropriate use of antibiotics and pesticides • Antibiotic resistant strains • Changes in weather patterns • Hantavirus

  26. Emerging Infectious Diseases • Contributing factors: • Modern transportation • West Nile virus • Ecological disaster, war, expanding human settlement • Coccidioidomycosis • Animal control measures • Lyme disease • Public Health failure • Diphtheria

  27. Epidemiology • The study of where and when diseases occur Figure 14.11

  28. Epidemiology

  29. Table 14.7

  30. Centers for Disease Control and Prevention (CDC) • Collects and analyzes epidemiological information in the U.S. • Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov Morbidity: incidence of a specific notifiable disease Mortality: deaths from notifiable diseases Morbidity rate = number of people affected/total population in a given time period Mortality rate - number of deaths from a disease/total population in a given time

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