| Gubbins et al. [30] |
Estimate prevalence of scrapie infection in GB based on an abattoir survey in 1997/1998 |
Simple age-structured prevalence model Probability of detection dependent on stage of incubation Diagnostic tests less than 100% specific |
Prevalence of scrapie 0.22% (95% CI: 0.01–0.97%) All tests used very specific (> 99%), with only one less than 100% |
| Gubbins [35] |
Estimate prevalence of classical scrapie in GB by integrating data on reported cases and the results of abattoir and fallen stock surveys for 2002 |
|
Prevalence ranges from 0.33% to 2.06% depending on stage of incubation at which diagnostic test able to detect infected animals Risk of infection much higher than the risk of clinical disease Analysis of surveillance data needs to account for PrP genotype |
| Gubbins and McIntyre [36] |
Estimate prevalence of classical scrapie in GB for 1993–2007 by integrating data on reported cases (1993–2007) and the results of abattoir and fallen stock surveys (2002–2007) |
Back calculation approach Probability of detection dependent on stage of incubation and PrP genotype Baseline risk of infection changes over time Frequency of PrP genotypes in a birth cohort changes over time Proportion of cases reported changes over time |
Prevalence was approximately constant for 1993–2003 and was estimated to be 0.3% to 0.7% depending on stage of incubation at which diagnostic test able to detect infected animals Prevalence declined by around 40% between 2003 and 2007 |
| Hopp et al. [44] |
Assess the efficacy of different strategies for identifying scrapie-affected flocks in Norway |
Stochastic simulation of strategy based on the probability of detecting an infected animal through each surveillance stream Includes effect of PrP genotype on risk of scrapie, incubation period and probability of detection |
Less than 9% of affected flocks are identified by either abattoir or fallen-stock surveillance Samples sizes much lower for fallen stock than abattoir surveys Abattoir surveillance most affected by an increase in test sensitivity |
| Webb et al. [78] |
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Simple age-structured prevalence model Probability of detection dependent on stage of incubation Stochastic simulation of survey |
Survey results consistent with a prevalence in the slaughter population of up to 11% Sample sizes need to be larger Diagnostic tests need to be assessed in relation to genotype and stage of infection |
