Hagenaars et al. [37]a
|
Obtain general insights into the population-dynamical properties of possible scenarios of scrapie transmission in a sheep flock |
|
-
Dependence of basic reproduction number (R
0) and generation time on other parameters gives insight into the effects of these parameters
-
Simplified model yields insights into interplay of horizontal and vertical transmission, and the characteristics of endemic scrapie
|
Hagenaars et al. [38]a
|
Understand how persistence of scrapie in a flock depends on transmission and flock size |
-
Stochastic model of within-flock transmission
-
Analytical calculations using branching-process approximations and
-
Numerical calculation using stochastic model simulations
|
|
Hagenaars et al. [39]a
|
Estimate transmission parameters from a scrapie outbreak |
Fitting stochastic transmission models to the outbreak data |
-
Mean incubation period for the outbreak is less than 1.5 years
-
Infectiousness of infected animals becomes appreciable at early stage of incubation
-
Difficult to quantify R
0: the data are consistent with a broad range of values
|
Matthews et al. [57]b
|
Examine the role of a range of epidemiologically important parameters and the effects of genetic variation in susceptibility |
|
-
Reduction in the frequency of the susceptible allele reduces R
0 most effectively when the allele is recessive
-
Inbreeding may increase R
0 when the susceptible allele is recessive, increasing the chance of an outbreak
-
Point estimate of R
0 for an outbreak in Cheviot sheep is given (R
0 = 3.9)
|
Matthews et al. [58]b
|
Analysis of a scrapie outbreak in a flock of Cheviot sheep |
Fitting a deterministic model to outbreak data |
|
Sabatier et al. [66] |
Explore the impact of genetic resistance and flock management practices on scrapie outbreaks |
Discrete-time deterministic mathematical model of the within-herd transmission dynamics of scrapie |
-
Three main observed patterns of outbreaks: sporadic, endemic and epidemic can be reproduced depending on parameter settings
-
Model results suggest that overall size of the outbreak is determined primarily by the initial genetic composition of the flock
-
Outbreak type is determined mainly by the herd management practices
|
Stringer et al. [71]b
|
|
Deterministic model defined using partial differential equations with respect to time, age and infection load |
|
Touzeau et al. [74]b
|
Explore hypothesis of increased scrapie transmission during lambing season |
|
|
Woolhouse et al. [79]b
|
Explore the course of an outbreak in a sheep flock, and the potential impact of different control measures |
|
-
In a closed flock, scrapie outbreaks may have a duration of several decades, reduce the frequency of susceptible genotypes, and may become endemic if carrier genotypes are present
-
In an open flock, endemic scrapie is possible even in the absence of carriers
-
Control measures currently or likely to become available may reduce the incidence of cases but may be fully effective only over a period of several years
|
Woolhouse et al. [80]b
|
Analysis of an outbreak of natural scrapie in a flock of Cheviot sheep |
Partial-differential equation model of scrapie within-flock transmission dynamics |
-
Model is able to reproduce key features of the outbreak, including its long duration and the ages of cases
-
Many infected sheep do not survive to show clinical signs
-
Most cases arise through horizontal transmission
-
Strong selection against susceptible genotypes
|