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Principles of Disease and Epidemiology

Principles of Disease and Epidemiology. How do we know you are sick let alone that its an epidemic?. Defining Some Terms. Pathology Study of disease Etiology Study of the cause of a disease Pathogenesis Development of disease Infection Colonization of the body by pathogens

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Principles of Disease and Epidemiology

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  1. Principles of Disease and Epidemiology How do we know you are sick let alone that its an epidemic?

  2. Defining Some Terms • 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. Symbiosis • Symbiosis is the relationship between organisms living together • Commensalism • one organism is benefited • the other is unaffected. • Mutualism • both organisms benefit. • Parasitism • one organism is benefited at the expense of the other.

  4. You as Ecosystem • Transient microbiota may be present for days, weeks, or months • Normal microbiota permanently colonize the host • 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: 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. Some Normal Flora

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

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

  10. Classifying Infectious Diseases • Symptom A change in body function that is felt by a patient as a result of diisease • 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.

  11. Classifying Infectious Diseases • Communicable disease spread from one host to another. • Contagious disease easily spread from one host to another. • Noncommunicable disease not transmitted from one host to another.

  12. 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.

  13. 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 infective

  14. The Stages of a Disease Figure 14.5

  15. 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

  16. 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

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

  18. Transmission of Disease Figure 14.6a & 8

  19. 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

  20. Transmission of Disease Figure 14.6b, c

  21. 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

  22. Relative frequency of nosocomial infections Figure 14.10

  23. Common Causes of Nosocomial Infections

  24. 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

  25. 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

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

  27. Principles of Disease Surveillance • www.who.int/emc/slideshows/Survintro/sld001.htm

  28. Epidemiology

  29. Methods

  30. Table 14.7

  31. 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

  32. CDC and MMWR • Centers for Disease Control and Prevention • Morbidity and Mortality Weekly Report • Published by the CDC • Weekly information on reportable diseases

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