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Principles of Disease and Epidemiology

14. Principles of Disease and Epidemiology. Principles of Disease and Epidemiology. Pathology : The study of disease Etiology: The study of the cause of a disease Pathogenesis: The development of disease Infection: Colonization of the body by pathogens

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Principles of Disease and Epidemiology

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  1. 14 Principles of Disease and Epidemiology

  2. Principles of Disease and Epidemiology • Pathology : The study of disease • Etiology: The study of the cause of a disease • Pathogenesis: The development of disease • Infection: Colonization of the body by pathogens • Disease: An abnormal state in which the body is not functioning normally

  3. Infection and Disease • ETIOLOGY –cause of disease • PATHOGENISIS-how the disease develops The Adventures of Sherlock Holmes, 20th Century Fox-1939 Basil Rathbone Nigel Bruce

  4. Infection and Disease • Infection and disease represents a balance. • A pathogen causes harm • A commensal can be part of the normal flora • The site in the body can determine the classification –E. coli in urine=bad; E. coli in colon = normal

  5. NORMAL MICROBIOTA

  6. Normal Microbiota and the Host • Locations of normal microbiota on and in the human body. Table 14.1c

  7. NORMAL MICROBIOTA • You can contain 1013 cells • You also contain 1014 cells that are bacterial • These make up normal and transient flora

  8. 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. Figure 14.1c

  9. Normal Microbiota and the Host • Microbial antagonism is a 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.

  10. MICROBIAL COOPERATION MICROBES • PERIODONTAL DISEASE

  11. OPPORTUNISTIC MICROBES • A good organism which gains entrance into a new site can be pathogenic

  12. Koch’s Postulates • Koch's postulates are used to prove the cause of an infectious disease. Figure 14.3 (2 of 2)

  13. Koch’s Postulates • Koch's postulates are used to prove the cause of an infectious disease. Figure 14.3 (1 of 2)

  14. Symbiosis • 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.

  15. SYMBIOSES

  16. 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.

  17. Classifying Infectious Diseases • Communicable disease: A disease that is 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.

  18. 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.

  19. Figure 14.4

  20. 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.

  21. Extent of Host Involvement • Local infection: Pathogens are 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.

  22. 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).

  23. 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

  24. The Stages of a Disease Figure 14.5

  25. 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

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

  27. Transmission of Disease Figure 14.6a, d

  28. 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.

  29. Transmission of Disease Figures 14.7b, 14.8

  30. Nosocomial (Hospital-Acquired) Infections • Are acquired as a result of a hospital stay. • 5-15% of all hospital patients acquire nosocomial infections. Figures 14.6b, 14.9

  31. Relative Frequency of Nosocomial Infections Table 14.5

  32. Common Causes of Nosocomial Infections

  33. NOSOCOMIAL INFECTIONS • In the United States, it has been estimated that as many as one hospital patient in ten acquires a nosocomial infection, or 2 million patients a year. Estimates of the annual cost range from $4.5 billion to $11 billion and up. Nosocomial infections contributed to 88,000 deaths in the U.S. in 1995. One third of nosocomial infections are considered preventable.

  34. NOSOCOMIAL INFECTIONS

  35. Emerging Infectious Diseases • Diseases that are new, increasing in incidence, or showing a potential to increase in the near future. • Contributing factors • Genetic recombination • E. coli 0157, Avian influenza (H5N1) • Evolution of new strains • V. cholerae 0139 • Inapproriate use of antibiotics and pesticides • Antibiotic resistant strains

  36. Emerging Infectious Diseases • Changes in weather patterns • Hantavirus • Modern Transportation • West Nile virus • Ecological disaster, war, and expanding human settlement • Coccidioidomycosis • Animal control measures • Lyme disease • Public Health failure • Diphtheria

  37. Crossing the Species Barrier UN 13.3

  38. Epidemiology • The study of where and when diseases occur Figure 14.10

  39. Epidemiology

  40. PLAY Animation: Epidemiology

  41. “AIDS” to “Gonorrhea”; “Pertussis” to “Streptococcal Toxic Shock Syndrome” Table 14.7 (1 of 2)

  42. “Haemophilus influenzae” to “Mumps”; “Streptococcus pneumonaie” to “Yellow Fever” Table 14.7 (2 of 2)

  43. Centers for Disease Control and Prevention (CDC) • Morbidity: Incidence of a specific notifiable disease. • Mortality: Deaths from notifiable diseases. • Morbidity rate: Number of people affected in relation to the total population in a given time period. • Mortality rate: Number of deaths from a disease in relation to the population in a given time.

  44. Centers for Disease Control and Prevention (CDC) • Collects and analyzes epidemiological information in the United States. • Publishes Morbidity and Mortality Weekly Report (MMWR) www.cdc.gov

  45. TERMINOLOGY REVIEW • Sign • Symptom • Syndrome • Communicable • Contagious • Non-communicable

  46. TERMINOLOGY REVIEW • Local • Systemic • Focal • Sepsis • Septicemia – bacteremia, viremia, toxemia • Primary, Secondary, Subclinical

  47. TERMINOLOGY REVIEW • Incidence • Prevalence • Sporadic • Endemic • Epidemic • Pandemic

  48. TERMINOLOGY REVIEW What was the incidence of Aids in 2005?

  49. TERMINOLOGY REVIEW • Acute • Subacute • Chronic • Latent • Herd Immunity

  50. Now We Have Disease! • Predisposing factors • Resistance • Incubation Period • Prodromal Period • Period of Disease • Period of Decline • Convalescence

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