Ecology of infectious diseases I

Question 1

Infectious disease is

Answer 1

the product of an interaction between two species; the pathogen and the host

Question 2

The host is a

Answer 2

resource for the pathogen

Question 3

y

Answer 3

proportion of the population that are infectious

Question 4

Give the equation for the tate of change of proportion of the population that are infectious

Answer 4

dy/dt = lambda(1-y) - mu x y
OR
dy/dt = By(1-y) - mu x y

Question 5

lambda

Answer 5

force of infection

Question 6

force

Answer 6

per capita risk

Question 7

B in equation

Answer 7

y / lambda

Question 8

B in words

Answer 8

a combination of parameters relating risk of infection to prevalence of infection

Question 9

Give the equation for B in directly transmitted pathogens

Answer 9

B = beta x N

Question 10

N

Answer 10

population size

Question 11

Beta

Answer 11

probability of transmission

Question 12

For directly transmitted pathogens, lambda =

Answer 12

beta x Ny

Question 13

Give the equation for lambda for sexually transmitted infections

Answer 13

lambda = c x beta x y
where y = the probability a partner is infected
and beta is the per partnership probability of infection

Question 14

c

Answer 14

average no. of partners

Question 15

Give the equation for lambda for vector-borne pathogens

Answer 15

lambda = ma^2bcHy

Question 16

m =

Answer 16

number of vectors per host

Question 17

a =

Answer 17

biting rate

Question 18

b =

Answer 18

proportion of infectious bites leading to infection

Question 19

c =

Answer 19

proportion of bites on infectious hosts leading to infection

Question 20

H =

Answer 20

average lifespan of vector

Question 21

Give the equation for B for vector-borne pathogens

Answer 21

B = ma2bcH

Question 22

mu =

Answer 22

death rate of host

Question 23

What is the equation for the plateau in a graph that measures proportion infected against time in arbitrary units

Answer 23

1 - (mu/B)
Or
1 - (1/R0)

Question 24

Describe the pathogenesis of Herpes Simples Virus

Answer 24

• subvirus enters peripheral sensory nerves
• migrates along axons to sensory nerve ganglia in the CNS
• allows virus to escape immune response, and become latent

Question 25

What happens post-latency

Answer 25

reactivation and spread to the surface for viral shedding

Question 26

Describe the VZV, EBV, CMV, HHV6 and HHV7 Herpesviruses

Answer 26

Primary infection generally occurs in a subclinical fashion in early childhood, with subsequent lifelong persistence of infection.

Question 27

Chickenpox

Answer 27

Varicella zoster virus

Question 28

A pathogen cannot invade a population unless

Answer 28

- dy/dt > 0 when y = 0 (OR z=0) - hence (B/mu) > 1

Question 29

R0 =

Answer 29

- B/mu OR - B/sigma

Question 30

R0

Answer 30

- the basic reproduction number - the average number of secondary cases generated by a primary case in a totally susceptible population - a fundamental measure of the transmission potential of a pathogen in a given setting

Question 31

If you integrate out the dy/dt equation, what happens

Answer 31

you get a logistic

Question 32

What is the equation for intrinsic growth rate

Answer 32

r = B - mu

Question 33

What is the equation for carrying capacity

Answer 33

K = 1 - (1/R0)

Question 34

Describe the SIR model of pathogenesis

Answer 34

- any individual in a population can be either Susceptible, Infected or Recovered (immune) - individuals that are born are fed into S (b) - individuals that die can leave at any stage (mu)

Question 35

Individuals that are Susceptible and Infected are related by

Answer 35

lambda - the risk of infection

Question 36

Those are Infected and Recovered are linked by

Answer 36

sigma - the rate of recovery

Question 37

Describe measles virus

Answer 37

- hemagglutinin - fusion protein - SH protein - matrix protein - polymerase - nucleoprotein - phosphoprotein

Question 38

Describe the dy/dt equation in light of the SIR model

Answer 38

dy/dt = By(1-z) - (sigma + mu) y

Question 39

S

Answer 39

1 - z

Question 40

Give the equation for dz/dt

Answer 40

By(1-z) - (mu x z)

Question 41

Give the equation for dS/dt

Answer 41

bN - (lambda x S) - (mu x S)

Question 42

Give the equation for dI/dt

Answer 42

lambda x S - (sigma x I) - (mu x I)

Question 43

Give the equation for dR/dt

Answer 43

(sigma x I) - (mu x R)

Question 44

Describe the similarities between pathogen-host dynamics and predator – prey systems

Answer 44

- cyclic (lag between consumption and resource renewal) - getting eaten = becoming immune - eating = infecting - transmission = predator reproduction

Question 45

Give some examples of viruses that broadly follow the SIR model (lifelong immunity with a short infectious period)

Answer 45

- measles - mumps - rubella

Question 46

Give some examples of viruses that broadly follow the SI model (lifelong carriage)

Answer 46

- HIV - herpesviruses - syphilis

Question 47

What is the aim of eradication?

Answer 47

reduce the average number of secondary cases generated by an index case to less than one

Question 48

How is eradication achieved?

Answer 48

- p immunised must exceed the fraction immune at equilibrium (in the absence of vaccination) - p > 1 - (1/R0)

Question 49

p

Answer 49

proportion

Question 50

Why is malaria so deadly?

Answer 50

it demonstrates antigenic variation and co-circulating strains