microbiology unit 4.1

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microbiology unit 4.1
2012-12-04 15:39:24

lucier @acc bio275 chapter 14: Disease and Epidemiology
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  1. Disease-
    abnormal state in which part or all of the body is not properly adjusted or is incapable of performing its normal functions
  2. Infectious Disease-
    disease resulting from a microbial infection
  3. •Pathogenicity:  
    the ability to cause disease
  4. Types of pathogens
    • 1. Primary Pathogen
    • 2. Opportunistic Pathogen
  5. Primary pathogen-
    causes disease in host is normal mode of operation
  6. Opportubistic pathogen
    Normally non-pathogenic, but can causes disease under certain conditions

    Example: perforated large intestine and gram negative bacteria
  7. Virulence-
    degree of pathogenicity
  8. Virulence factors-
    Characteristics of microbe that make it pathogenic
  9. Infection
    microbe growing in/on its host.
  10. Infectivity-
    ability to establish a discrete point of infection
  11. Invasiveness-
    ability to spread from initial site of infection
  12. Epidemiology-
    study of disease in populations
  13. 1848-1840 outbreak of cholarea in London was researched by... where he....
    John Snow....indentified contaminated water from the Board Street pump as the source of the outbreak
  14. Who used statistical data to argue for improved conditions in British military hospitals?
    Florence Nightingale
  15. Prevalence=
    number of individuals with the disease at a given time

    “snap shot” of population at one time point
  16. Mortility
    • number of individuals in the population who die from a particular cause in a given time interval
  17. Case Fataity Rate-
    proportion of infected individuals who will be killed by the disease
  18. Morbidity and CFR data can help you make decisions on how to allocate resources
    which diseases are more significant threats at any given time in a particular populationexample: a disease with low CFR and high morbidity may be more of a threat than a very high (100%) CFR with very low morbidity
  19. •Frequency

    • disease is always present in the population
    • •prevalence usually varies 
    • •cyclic seasonal variations are common in many 
    • •humans can act as reservoirs
  20. Frequency

    • infected individuals are not always present in the population
    • •non-human reservoirs exist 
    • •isolated from populations in which it is endemic
  21. Outbreak-
    significant increase in prevalence of a disease
  22. Epidemic-
    outbreak of more or less limited geographic extent
  23. Pandemic-
    outbreak that involves several continents, or world-wide
  24. Epidemiological Surveillance
    • •Many governments have agencies
    • that collect and analyze epidemiological data.

    • –United States: Centers for Disease Control and Prevention (CDC)
    • •Headquarters in
    • Atlanta, GA
    • •Collects data and does research on pathogens world-wide
    • •publication: Morbidity and Mortality Weekly Report (MMWR) - available free online
  25. Notifiable Diseases
    –cases of certain diseases must be reported to the CDC

    –establish long-term patterns

    –early recognition of potential outbreaks

    •possibility of quick containment
  26. Gather information about a disease (4)
    –reservoirs and modes of transmission

    –who is most at risk (predisposing factors)

    –best methods for control

    –how best to use limited resources to combat disease
  27. Reservoirs
    • sources of disease organisms in the environment
    • –Humans

    •individuals showing S & S

    •carriers - infected but without serious S & S

    –chronic, latent, subacute, subclinical, asymptomatic, incubation

    –examples: HIV, diphtheria, hepatitis, gonorrhea, streptococcal infections, typhoid fever

    • •eradication may be possible for diseases with humans as the only reservoir, and if an effective vaccine is available
    •    –smallpox (variola) - late 1970s
    •    –poliovirus - close 
  28. Resevoirs cont..

    –zoonoses: can cause disease in animals and can be transmitted to humans

    •over 150 known:  Table 33.1

    •control is difficult if in wild animal populations

    –some have no visible effect on infected animals

    •Trypanosomes and game animals in Africa
  29. •Non-living Reservoirs
    –to be a reservoir, microbes must be capable of long term survival and reproduction in these environments

    • –Examples
    • •soil and water
    • •food
  30. Transfer mechanisms can be classified into two major categories.
    –Direct Contact

    –Indirect Contact
  31. Transmission photo
  32. Direct Contact
    person to person

    staphylococcal infections, measles, cold viruses, influenza, STDs
  33. Indirect Contact-Fomites
    –contact contaminates an inanimate object that is contacted by an uninfected host

    •towels,utensils, drinking cups, money, syringes, etc
  34. Droplet Transmission-
    –droplet: larger mucus and saliva particles that remain airborne for only short distances

    •usually less than one meter after coughing

    –example: influenza
  35. Airborne Transmission
    –agents on tiny particles that can remain airborne for long periods of time

    •dust, mucus, saliva, aerosols

    • •longer exposure
    • to drying, UV, lack of nutrients

    –measles, tuberculosis, Legionella, Streptococcus, fungal spores (systemic infections)

    –entry by ingestion, inhalation, through cuts in skin
  36. Vehicle Transmission-Contaminated Food and/or Water
    –Fecal/Oral transmission: exit host in feces, enter new host by ingestion of contaminated food or water

    •many examples: mostly gastrointestinal diseases

    –Shigella, Salmonella, enteropathogenic E. coli, cholera, Norovirus, Polio, amoebic dysentary

    •associated with poor sewage and drinking water treatment, and unsanitary food preparation techniques
  37. Vector Transmission (2 types)
    • Mechanical Transmission
    • Biological Transmission
  38. Mechanical Transmission-
    passive transport on surface of animal.

    Ex. Houseflies and fecal microbes
  39. Biology Transmission-
    specific association btwn a particular animal and a microbe.

    Most vectors are blood sucking anthropods. Ex. fleas, mosquitos, tickes, flies, lice
  40. Vector Transmission-
    –Vector control is often a viable strategy for control of these diseases

    –Range of vector often determines where a disease can occur

    –examples: Table 14.3

    • •Plasmodium and
    • Anopheles mosquitoes

    •Rickettsias and ticks

    •Typhus and lice or fleas

    •Lyme disease and deer ticks
  41. Spread of Disease-
    •Common Source Diseases:

    –infection from contaminated, non-living source

    •examples:  most food poisoning, food infections

    –less likely to become epidemic/pandemic

    –rapid, localized increase and rapid decline after identification and treatment of source
  42. Spread of Disease- Propagated Diseases
    –spread by contact with infected individual (direct, droplet, airborne) or by vectors

    –slower increase that may be less localized

    –greater potential to become epidemic/pandemic

    –more difficult to identify early and to control once it begins to spread

    •made worse by modern transportation systems
  43. Emerging Infectious Diseases...Diseases are increasing in prevalence..why?
    –return of previously better controlled microbes

    •drug resistance  (malaria, staph and strep)

    •new pool of susceptible individuals (TB in HIV patients in US and western europe)

    •breakdown in public health measures
  44. Emerging Infectious Diseases
    –Evolution of microbes: new species that infect humans


    –Humans interact with the surrounding environment in new ways - changes frequency and pattern of contact with microbes.

    •Lyme Disease: predator depletion and suburban lifestyle

    •changes in patterns of human habitation and hemorrhagic diseases such as ebola and hantavirus
  45. Emerging Infectious Diseases- Lifestyle Changes:
    Legionnaire's Diesease and air-conditioning systems
  46. Emerging Infectious Diseases- Climate Change-
    Global warming and changes in vector ranges.