7. Infection transmission Flashcards Preview

ESA 2 - Infection > 7. Infection transmission > Flashcards

Flashcards in 7. Infection transmission Deck (15)
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1
Q

What is a ‘common source’ in terms of infection?

A

Source (environmental, food/water, animal, human) of infection that gives rise to a number of cases in 1 area.

2
Q

Give an example of indirect person-to-person transmission.

A

malaria transmitted person-to-person via a vector (female mosquitoes)

3
Q

What is the endemic level of a disease?

A

the usual background rate of a disease in a community

4
Q

What is a disease ‘outbreak’?

A

2 or more cases linked in time and place

5
Q

What is a disease ‘epidemic’?

A
  • rate of infection greater than usual background rate

- caused by antigenic drift (accumulation of mutations within genes that code for antibody-binding sites)

6
Q

What is a disease ‘pandemic’?

A
  • very high rate of infection spreading across many regions (e.g. countries/continents)
    • caused by antigenic shift (2 or more different strains of a virus combine to form a new subtype having a mixture of the surface antigens of the original strains)
7
Q

What viral characteristic determines the size of an outbreak?

A

Basic reproduction number (R0): average no. of cases 1 case generates over the course of its infectious period, in an otherwise uninfected, non-immune population.
If R0 >1 - increase in cases
If R0 = 1 - stable no of cases
If R0 <1 - decrease in cases

8
Q

Name 3 possible reasons for outbreaks/epidemics/pandemics.

A
  1. new pathogen (or antigens/virulence factors/antibacterial resistance)
  2. new hosts (immunocompromised, healthcare effects)
  3. new practice (social eg tattoos, healthcare)
9
Q

What is the infectious dose of a pathogen? How does this vary?

A

No. of microorganisms required to cause infection. Varies by:

  • microorganism
  • presentation of microorganism
  • immunity of potential host
10
Q

Give an example of a pathogen with a very high and a very low infectious dose.

A
  • very high: salmonella (>10^5 organisms)

- very low: E. coli (<10 organisms)

11
Q

What interventions at the pathogen/vector level can reduce transmission?

A
  1. reduce/eradicate pathogen
    - antibacterials, inc. disinfectants
    - decontamination
    - sterilisation
  2. reduce/eradicate vector
    - eliminate vector breeding sites
12
Q

What interventions at the patient level can reduce transmission?

A
  1. improved health
    - nutrition
    - medical treatments
  2. immunity
    - passive, e.g. maternal antibody, intravenous immunoglobulin (e.g. for immunocompromised)
    - active, i.e. vaccination - protects individual and herd immunity
13
Q

What interventions at the practice level can reduce transmission?

A

avoidance of pathogen or its vector

  1. geographic (‘don’t go there’)
  2. protective clothing, equipment, e.g.
    - long sleeves against mosquito bites
    - personal protective equipment in hospitals(gowns, gloves, masks)
  3. behavioural
    - safe sex
    - safe disposal of sharps
14
Q

What interventions at the environmental level can reduce transmission?

A

environmental engineering: safe water, safe air, good quality housing, well-designed healthcare facilities

15
Q

What are positive and negative consequences of disease transmission control?

A

Good:
i) decreased incidence or elimination of disease/organism (smallpox, polio, dracunculiasis)

Bad:

i) decreased exposure to pathogen… decreased immune stimulus… decreased antibody… increased susceptibility… outbreak
ii) later average age of exposure… increased severity