vaccines epidemiology wk2

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  1. variolation
    transfer of pustular material to shallow cuts in the skin
  2. father of vaccination
    • Edward Jenner - cow pox/smallpox ("vacca" = cow)
    • (Louis Pasteur in 1800s, Fowl Cholera, Anthrax and Rabies)
  3. duration of vaccines for different microbes
    vaccines > bacteria > parasites
  4. three kinds of live vaccines
    • attenuated/modified-live: genetically engineered to be avirulent
    • Heterotypic: different organism with similarities (cowpox vs smallpox, etc)
    • vectored: made using recombinants, put gene from another pathogen into a vector to kick off immune
  5. three categories of vaccines
    • live
    • killed
    • subunit
  6. bacterins
    whole killed bacteria used as a killed vaccine
  7. chemical methods of inactivating microbes to become virus
    • protein fixatives: cross-linking agents like formalin, organic solvents like phenol/alcohol/acetone
    • alkylating agents: iodoacetate, beta-propriolactone
    • aziridine compounds: binary ethyleneimine
    • lipid solvents: "split vaccines" against enveloped virus, takes the envelope off with a detergent like either, or non-ionic detergents like Triton X-100
  8. subunit vaccines
    • made to stimulate immune against a PART of a microbe
    • bacterial virulence determinants: adhesions (fimbrae), toxoids (inactivated toxins), agglutinins, polysaccharide capsular material
    • surface proteins on viruses and parasites: viral envelope proteins (Hep B), protozoan surface antigens
  9. toxoids
    inactivated toxins, used in subunit vaccines
  10. recombinant vaccines
    • genetic engineering to create better vaccines
    • subunit antigens, live recombinant vaccines (rationally attenuate vs vectored), genetic/DNA vaccines
  11. recombinant subunit antigens
    recombinant proteins made in cultured cells, stimulates immune against microbe based on one part
  12. pseudorabies is a type of which vaccine?
    rationally attenuated
  13. rationally attenuated pathogens
    live pathogens with the genetic material altered to reduce virulence
  14. vectored vaccines
    • live attenuated viruses or bacteria (vectors) carrying genes for protective antigens from pathogenic microbes
    • canarypox/avipox often used as a vector--causes very mild disease in mammals (our rabies and distemper are canarypox based)
  15. genetic (DNA) vaccines
    • inject naked DNA into animal, taken up and made.  
    • Plasmid DNA vectors carrying genes for protective antigens from pathogenic microbes
    • West Nile Virus in horses
  16. passive immunization
    Hyper-immunize mom in last trimester to increase immunoglobulins in colostrum, make sure progeny get enough colostrum
  17. combination (multivalent) vaccines
    vaccines that target multiple pathogens or multiple strains of the same pathogen in a single formulation or dose
  18. autogenous vaccines
    • made from pathogens found in an individual, herd or geographical location and can only be used in that particular herd/flock
    • custom for one farm
  19. conjugate vaccines
    vaccines where antigen is covalently linked to a substance that enhances immunogenicity (double antigens for more potent vaccine)
  20. herd immunity
    effect on vaccinated animals have in protecting unvaccinated animals in a herd/population (lost when vaccinations are low)
  21. altruistic vaccine
    vaccine that blocks transmission (provides little benefit to vaccinated individual
  22. adjuvent
    • a substance that boosts immunogenicity to co-administered antigens
    • typically contain a carrier substance (like alum), an immunomodulary substance, or both.
  23. ring vaccination
    • associated with eradication programs
    • mass vaccinations in a circle around infected person or location
  24. core vaccines
    • high enough benefit and low enough risk to be used in most patients
    • used for diseases that are: endemic to a region, of public heath significance, required by law, virulent/highly infectious, pose a risk of severe disease
  25. epidemiology
    study of disease in populations and factors that determine occurrence
  26. exposed
    individual that has met with an infectious agent in a way we know from experience may cause disease
  27. epidemic
    • aka outbreak
    • sudden, usually unpredictable increase in numbers of cases of infectious disease in a population.  Frequency greater than expected
  28. endemic
    disease occurs at expected frequency (often predictable).  Always present in population, usually at a stable low level
  29. pandemic
    epidemic over multiple countries
  30. sporadic
    disease occurring irregularly and halfhazardly; appropriate circumstances have occurred locally that produced small localized outbreaks
  31. vertical transmission
    infections transmitted from one generation to the next by infection of embryo or fetus while in utero (mammals) or in ovo (birds, reptiles, amphibians, fish, arthropods)
  32. horizontal transmission (direct vs indirect)
    • infections transmitted from any segment of a population to another (one puppy to another, zoonoses, etc)
    • Direct is when a susceptible host contracts through physical contact with infected host
    • indirect involves intermediate (living = vector or inanimate = fomite)
  33. vector vs fomite
    vectors are living, fomites are inanimate
  34. reservoir
    any animal species, insect, soil or combination of these in which the infectious agent normally lives and multiplies so that it can be transmitted to a susceptible animal
  35. resistance
    all of body's defenses against infection (relative for most diseases--enough will overcome almost anything)
  36. immunity (and 2 types)
    • resistance associated with cells or antibodies of the immune system.  Can be active or passive.
    • active: immunity acquired by previous exposure to antigens of agent (previous infection or vaccination).  Can be life-long or just a few years.  
    • passive: acquired through transfer of antibodies like colostrum, transplacental transfer or administration of hyperimmune serum (generally short)
  37. infectiousness depends on
    • duration of contagious period
    • amount of infectious agent an animal can transmit
  38. latent period (prepatent period)
    time lapse between infection and ability to transmit
  39. carrier
    individual who harbors the organism but without clinical symptoms (subclinical)
  40. incubation period
    • period of time between infection and development of CLINICAL SIGNS (not infectiousness).  
    • Subclinical infections have latent period but not incubation period (because never have clinical signs
  41. subclinical infection
    able to transmit virus but don't have clinical signs (ever, not a stage but an endpoint).  Have latent period but not incubation period.
  42. model
    • simplified version of a complex phenomenon
    • animal models
    • mathematical models
  43. SI
    susceptible to infectious (rabies in Foxes)
  44. SIS
    • susceptible to infectious back to susceptible (e. coli in cattle, common cold)
    • No immune/recovered period, straight back to susceptible
  45. SIR
    • susceptible, infectious, recovered.  Never susceptible again
    • Malaria in humans, H1N1 in pigs
  46. SIRS
    • susceptible, infectious, recovered, susceptible
    • salmonellosis in cattle, seasonal flu.  Immune for a minute, then can get again
  47. SEIR
    • susceptible, infEcted, infectious, recovered
    • measles, chicken pox, FMD
    • infected period before being infectious, lifelong immunity
  48. SEIRS
    • susceptible infEcted, infectious, recovered, susceptible
    • infected period before becoming infectious, short immunity then back to susceptible (seasonal flu, ebola, equine influenza)
  49. Chance in mathematical modeling
    deterministic vs stochastic
  50. time in mathematical modeling
    • difference equations (discrete time steps like weeks, etc)
    • vs
    • differential equations (continuous time)
  51. differential equations
    • rate of change of y (like number of infectious individuals) with respect to x (time)
    • rate of change in number of individuals in a given category (infectious individuals) is given by 
    • + the number who enter it
    • - the number who exit it
  52. transmission rate/transmission coefficient
    • beta = cp (rate of susceptible to infectious)
    • c is probability of contact between susceptible and infectious during the time interval and
    • p is the probability of transmitting infection when contact occurs (required infectious dose and attack rate = cases/exposed)
    • we rarely know C, so we just try to make beta fit.
  53. rate a (infectious to recovered)
    rate of leaving the infectious state to enter recovered state = inverse of duration of infectious state (10 days of illness = 1/10)
  54. how to measure ease/sped of infection spread (SIR)
    • duration of infection
    • x
    • number of new infections produced per unit time
    • number of new infections per infectious host during whole infection period (does not include time specifically)
  55. basic reproduction number (R0)
    • expected number of secondary cases produced by typical infected individual during entire infectious period in completely susceptible population (only applies at the beginning)
    • Later, use R0*x where x is fraction of host population that is susceptible)
    • R0 = (betaN/a) = cnN/a
    • betaN is number of new infections each infectious host produces per unit time
    • 1/alpha = duration of infection
    • only applies to early stage of the outbreak
  56. R0 rules
    • R0>1 = exponential growth, epidemic
    • R0=1 = stable growth, endemic
    • R0<1 = incidence decreases over time, transmission eventually eliminated
  57. trying to make R0<1
    • decrease alpha (duration of infection) by treatment or culling, vaccination
    • decrease beta by decreasing contacts (quarantine, isolation, decreased stocking density) Or decrease probability of susceptible catching infection by vaccination
  58. For infection to persiste, proportion of susceptibles must be greater than
    • 1/R0 
    • If R0 = 10, infection will persist is susceptible is >10%
    • What proportion vaccinated for herd immunity?  H=1-1/R0
  59. Herd immunity threshold
    • H = 1-1/R0
    • minimum number we need to vaccinate to keep infection from spreading
    • (if R0 is 2, we end up with 0.5, must vaccinate at least 50% of pigs)
  60. vector-borne disease models require
    modeling two populations (vector and susceptibles)
  61. link between herd immunity threshold (H) and R0
  62. effective reproduction number (R)
    R0*x where x is fraction of host population that is susceptible

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vaccines epidemiology wk2
2016-10-05 12:55:08

IV wk2
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