epidemiology 23-28

Question 1

what are microparasites?

Answer 1

parasites which are small and multiply inside their host

Question 2

what are macroparasites?

Answer 2

large parasites that multiply externally of the host

Question 3

what are DALYs?

Answer 3

• disability adjusted life years
• the number of healthy years of life lost due to premature death and disability

Question 4

what is an epidemic?

Answer 4

an increase in incidence of disease in excess of that expected

Question 5

how is R0 calculated?

Answer 5

R0 = p x c x d
p - the probability that a contact results in transmission
c - the frequency of host contacts between infectious and susceptible individuals
d - the average amount of time the host is infectious

Question 6

what is the definition of R0?

Answer 6

the average number of new cases arising from 1 infectious case introduced into a population of wholly susceptible individuals

Question 7

how is the effective R calculated?

Answer 7

Re = R0 * fraction of susceptible individuals

Question 8

how do epidemics continue?

Answer 8

• susceptible population increases:
  -> more people are born
  -> migration into a population
  -> no immunity
• the pathogen mutates and can reinfect or continually infect individuals
• immunity wanes

Question 9

what is the index case?

Answer 9

the first case in an outbreak of disease

Question 10

what is meant by the incubation period?

Answer 10

the period between infection and clinical onset of disease

Question 11

what is the latent period?

Answer 11

the time from infection to infectiousness

Question 12

what is a point epidemic?

Answer 12

• a single common exposure and no incubation period
• does not spread by host-to-host transmission
• usually food contamination

Question 13

what is a continuous common source epidemic?

Answer 13

• prolonged exposure to source over time
• cases do not occur within the span of a single incubation period
• e.g. water borne cholera

Question 14

what is a propagated progressive source epidemic?

Answer 14

• spread between hosts
• larger curves are seen until susceptibles are depleted or intervention is made

Question 15

how is an endemic equilibrium maintained

Answer 15

• stability in the incidence of infection
• persistence of the parasite in the host population
• each infection produces 1 secondary infection on average

Question 16

how is S calculated at endemicity

Answer 16

S = 1/R0

Question 17

what do determinants of persistence depend on?

Answer 17

• critical community size
• rate of contact for transmission
• duration of infectious period
• survival of host

Question 18

what is the critical community size?

Answer 18

the minimum host population size required for the pathogen to persist

Question 19

what is the definition of R0 for macroparasites?

Answer 19

the average number of female offspring produced through the lifespan of one female worm that survives to maturity in the absence of density dependent constraints on population growth

Question 20

how is herd immunity reached? can it be reached without intervention?

Answer 20

• achieved by vaccination and intervention
• a pathogen that generated total herd immunity would go extinct, which goes against evolution

Question 21

what is vectorial capacity?

Answer 21

the average number of potentially infective bites that will be delivered by all the vector’s feeding upon a single host in one day

Question 22

how is R0 calculated for vectors

Answer 22

R0 = c * d
c = vectorial capacity
d = duration of host infectiousness in days

Question 23

how can vector transmission be controlled?

Answer 23

• human bait traps
• non human bait traps
• urban breeding site source reduction
• rural drainage of breeding sites

Question 24

how do GM mosquitoes prevent transmission?

Answer 24

the males are sterile so offspring cannot be produced

Question 25

why are vector borne diseases most affected by climate change?

Answer 25

• environmental parasite stages are particularly sensitive to the climate
• parasite development is often climate dependent

Question 26

how long does the extrinsic incubation period need to be for a vector to be infectious?

Answer 26

it needs to be shorter than the average adult life expectancy of the vector

Question 27

how can ENSO be responsible for periodic epidemic cycles?

Answer 27

• flooding increases water breeding grounds for mosquitoes
• higher temps increases the proportions of vectors surviving the feeding cycle
• expanding into other places due to warmer climate

Question 28

what is the R0 of SARS-CoV-2 estimated to be?

Answer 28

between 2 and 4

Question 29

what is the definition for vaccine efficacy?

Answer 29

the percentage of those vaccinated who subsequently become immunised