Chapter 16

• Epidemiology


  The study of factors that influence the spread and causes of disease in populations
• Epidemiologists


  • Collect data about sources of disease and risk factors
  • Strategies to prevent/ predict spread of disease
  • Expertise in ecology, microbiology, sociology, statistics, and psychology
• Communicable (contagious) diseases


  Transmission from one host to another
• Transmission


  Can be direct or indirect
• Non-communicable diseases


  Do not spread from host to host
• Fomites


  Any object used to transmit microbes
• Reservoir


  • Natural habitat of pathogen, where pathogen resides
  • Nonliving or living
  • In or on animal, human, or environment
• Human Reservoir


  • Symptomatic infections: clear source of pathogens
  • Disease may spread before symptoms appear or after they go away
  • Asymptomatic infections: harder to identify, carriers may not notice infection, spread to others
  • Immune system may be responding to pathogen, inhibiting expression of symptoms
  • Potential pathogens may be part of normal microbiota
  • Active carrier- infected individual, transmits disease
  • Passive carrier- non-infected individual, transmits disease
• Non-human animal reservoir


  • Difficult to control in wild animal populations
  • Zoonoses, exist in mostly animals, transmitted to humans
  • Most severe in humans; no evolution
• Environmental reservoir


  • Difficult or impossible to eliminate
• Chain of Infection


  1. Portal of exit: body surface or orifice: exit route for pathogen

  2. Disease transmission: Vertical transmission, Horizontal transmission

  3. Direct transmission: immediate transfer of infectious agent to portal of entry

  4. Vehicle Transmission: transmission of pathogens via water, food, air

  5. Indirect transmission: Airborne, Vehicle borne, Vector borne
• Portal of Entry


  Body surface or orifice: entry route for pathogen
• Characteristics of the pathogen

  • Virulence: ability to cause disease
  • Dose: number of pathogens introduced, minimum number of pathogens needed to cause symptoms
  • Incubation period: influences the extent of spread
• Epidemiological Studies


  • Descriptive studies
  • Analytical studies
  • Experimental studies
• Factors that affect the spread of disease

  • Population characteristics: Immunity, General health, Age, Gender, Religious or cultural practices, Genetic background
• CDC


  • Center for Disease Control
  • Provide support for infectious disease labs in the US
  • Collect data on disease of public health importance
  • Research related to infectious disease
  • Personnel for support in disease outbreak situations
• WHO


  • World Health Organization
  • Provide worldwide guidance in field of health
  • Set global standards for health
  • Strengthen national health programs
  • Develop and transfer appropriate health technology
• Symptomatic infections


  Infections that produce noticeable symptoms, making them easier to identify as a source of pathogens. However, it's important to note that disease can spread before symptoms appear or after they go away.
• Asymptomatic infections


  Infections that do not produce noticeable symptoms, making them harder to identify. Carriers of asymptomatic infections may not even realize they are infected, which can lead to the spread of disease.
• Passive carrier


  A non-infected individual who can transmit the disease, often because the pathogen is part of their normal microbiota.
• Active carrier


  An infected individual who can transmit the disease.
• Vertical transmission


  Transmission of a pathogen from parent to offspring, often through the placenta or during childbirth through breast milk.
• Horizontal transmission


  Transmission of a pathogen between members of the same generation, either through direct or indirect contact
• Direct transmission


  Immediate transfer of an infectious agent to a portal of entry through close contact with an infected person or object
• Vehicle transmission


  Transmission of a pathogen through a vehicle, such as water, food, or air
• Vector borne transmission


  Transmission of pathogens through a living organism, such as a mosquito or tick, that carries the pathogen from one host to another. Type of Indirect Transmission. Can be a mechanical or biological vector.
• Indirect transmission


  Transmission of a pathogen through a vehicle, but with an intermediary step; three types: airborne, vehicle borne, and vector borne
• Orifices


  Another example of a portal of entry, where pathogens can enter the body through openings such as the mouth, nose, and eyes
• Body Surface


  An example of a portal of entry, where pathogens can enter the body through cuts, abrasions, or other breaks in the skin
• Descriptive studies


  characteristics of an outbreak; person, time, place
• Analytical studies


  Examine the relationship between a potential risk factor and the health event.
• Experimental studies


  Effectiveness of a specific treatment. Establish a cause-and-effect relationship. Manipulating the exposure and measuring the outcome in a controlled setting.