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ZOOL 352 > Lec 20-21: Epidemiology > Flashcards

Lec 20-21: Epidemiology Flashcards

1
Q

What did Daniel Bernouli (1766) do for the field of epidemiology?

A

created math models to analyze dynamics of smallpox epidemic in Paris

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2
Q

Epidemic or outbreak=

A

disease occurrence among a population that is above what’s expected at a given time & place

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3
Q

Cluster=

A

a group of cases in a specific time & place that might be more than expected

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4
Q

Endemic=

A

disease or condition present among a population at all times (constantly present at a steady rate)

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5
Q

pandemic=

A

a disease or condition that spreads across regions/ countries

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6
Q

rate (in terms of epidemiology)=

A

of cases occurring during a specific period; always dependent on the size of the pop during that period
- prevalence vs incidence

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7
Q

T/F

  1. An endemic disease is constantly present in a pop, with a predictable rate of spread
  2. An epidemic disease is characterized by a sudden increases in cases across the world
  3. A pandemic disease is characterized by a sudden increase in cases across several countries or the world
A
  1. true
  2. false. epidemic= sudden increase in cases spreading through a large population (but not worldwide)
  3. true
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8
Q

Explain the epidemiological triangle

A

This is used as a tool to address the 3 components that contribute to the spread of the disease

  1. Environment (climate, sanitation, health care, etc)
  2. Host (genetics, age, sex, health, previous infections, etc)
  3. Agent (pathogen, parasite, virus)
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9
Q

The reproductive number (R0) represents a threshold for disease spread. Explain the different values and what the thresholds might be

A

R less than 1: self-sustaining epidemic is not possible (parasite will disappear)

R=1: parasite will barely persist

R greater than 1: parasite will persist and tend to spread (epidemic)
** transmission threshold**

R much greater than 1: parasite will be difficult to eradicate

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10
Q

Is the basic reproductive number fixed?

A

No!

Different aspects of parasite transmission can affect it, and may change over time

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11
Q

For microparasites, what determines its persistence in host populations?

A

Can each infection replace itself?

Determined by R0= # of secondary infections produced by one infected host introduced into a pop comprising only susceptible hosts

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12
Q

For macroparasites, what determines its persistence in host populations?

A

Can each individual replace itself?
Determined by R0= # of new females produced by 1 female in absence of density-dependent constraints

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13
Q

Give the 3 factors that influence R0

A
  1. duration of infectious period
  2. # of susceptible people in the population (contact rate)
  3. mode of transmission (eg airborne vs spread by bodily fluids etc)
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14
Q

Rank the following diseases from highest to lowest reproductive number

Ebola
Rabies
Fly
Measles
Chicken Pox

A

Measles
Chicken pox
Ebola
Flu
Rabies

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15
Q

If a disease has a higher reproductive number, does it require a higher or lower % of the population to be vaccinated in order to eradicate it?

A

higher R0= higher vacc % required

eg. Malaria and Measles required near 100% vacc to eradicate

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16
Q

T/F

R0 can estimate the proportion (p*) to be vaccinated or otherwise treated in order to eradicate the infection

A

true

p*= 1-1/R0

17
Q

What does R0 determine?

A

The ability of parasites to regulate host population

Outbreak of epidemics, persistence of endemic infections, & whether or not the parasite dies out

18
Q

Give the proportionality for the basic reproductive number

A

R0 is directly proportional to (infection/contact) x (contact/time) x (time/infection)

basically, transmissibility x avg rate of contact x duration of infectiousness

It’s directly proportional, so if one of these increases, so does R0 (and vise versa)

19
Q

Give the equation to calculate Ro for MICROparasites

A

Ro=β(H) / b + a + y

β= rate of transmission
H= density of susceptible hosts
b= natural host mortality
a= parasite-induced host mortality
y= host recovery rate

B and H= directly related to Ro
b, a, and y= inversely related to Ro

20
Q

Give the equation to calculate Ro for MACROparasites

A

Ro=βλH / (μ+b+α) (y+βH)

β= rate of transmission
λ= parasite per capita birth rate
H= density of susceptible hosts
b= natural host mortality
μ= parasite per capita death rate
α= parasite-induced host mortality

21
Q

What kind of important questions can modelling epidemics answer? Lots of options, give 2-3

A

What is the risk of an epidemic to occur?

How far will it spread?

How long will it last?

What impact does a particular intervention have on the risk, severity, and duration of the epidemic?

22
Q

For microparasites, β x SI=

A

rate at which susceptible hosts become infected

β = infectiousness (transmission rate)
SI= contact rate

23
Q

Give an SIR compartmental model

A

Susceptible —–> Infectious —-> Recovered

S–> I is based on β
I –> R is based on y (rate of recovery)

R –> S is the rate of recovery with no acquired immunity

24
Q

What is a variation of the SIR model?

A

SEIR model

Susceptible, exposed, infected, recovered

25
Q

T/F

In general, in highly endemic areas, children become infected at a very early age

A

true

BUT
- rates of infection or recovery are likely to vary w age
- assumes a type II survival curve (constant risk of mortality independent of age)
–> type I survival curve is more realistic (mortality increases with age)

26
Q

Immuno-epidemiology=

A

how immune responses, especially acquired immunity, affect the population dynamics of host-parasite interactions and parasite population structure

27
Q

Give 4 factors that need to be considered for immuno-epidemiology

A
  • extent of herd immunity
  • degree of cross-immunity
  • genotypes of hosts and parasites
  • stochastic effects
28
Q

T/F
Particular contacts and the frequency of contacts varies
considerably among host individual. BUT this variation doesn’t follow any certain pattern

A

false

this variation does follow certain patterns

29
Q

Does latency reduce or increase Ro?

A

higher latency period= reduced Ro

time between recurrences of the epidemic waves extended

30
Q

Do sexually transmitted infections depend on frequency or density dependent transmission?

A

frequency-dependent transmission

directly proportional to # of sexual contacts

31
Q

Life expectancy and age of infection are added as extensions of the standard SIR model. Give the new equation

A

Ro = 1 + (β(I)/µ) which = 1 + (L/A)

β(I)= rate susceptibles become infected
1/µ= life expectancy= L
1/ β(I)= A= age of infection

32
Q

T/F

If the average age of infection is higher, Ro would increase

A

false
would decrease

33
Q

Give 5 problems with the basic SIR model

A
  1. Assumes every person will encounter every other with equal probability (not true)
    - heterogenous contact patterns: some contacts more likely than others, & contact patterns change with habits etc
  2. Assumes direct mode of transmission
    - even within subgroups contact modes can vary
    - depends on non-biological aspects of transmission risk (change in contact patterns)
  3. Role of chance is not accounted for!
  4. The population is fixed
  5. Latent period= 0
34
Q

When considering the behavior or a microparasite endemic, what are the 2 possible outcomes?

A
  1. epidemic followed by parasite disappearance
  2. epidemic followed by endemic infection
35
Q

Describe the behavior of a microparasite in outcome 1: epidemic followed by parasite disappearance

A
  1. intro of parasite to entirely susceptible host pop. Inc contact rate b/w infected & noninfected= rapid spread
  2. pool of susceptible hosts depleted rapidly –> immunity increases, so # of infected individuals decreases
  3. lower contact rate= fewer new cases. Too few new susceptibles to sustain epidemic
  4. epidemic dies out
  5. # of susceptibles will begin to increase
36
Q

Describe the behavior of a microparasite in outcome 2: epidemic followed by endemic infection

A
  1. intro of parasite to entirely susceptible host pop. Inc contact rate b/w infected & noninfected= rapid spread
  2. Pool of susceptibles is depleting rapidly, fewer infected hosts as immunity sets in; lower contact rate
  3. epidemic dies out
  4. intro of new susceptibles –> new infections @ a lower rate
  5. susceptibles are not depleted as rapidly, so some level of new infections can persist
37
Q
A

ZOOL 352 (11 decks)

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