Standard statistical analyses suggest (with 95% confidence) that the prevalence of detectable (by histopathology) infection in the slaughter population was ≤0.11%.
Using the model, we demonstrate that the negative results obtained for all samples using IHC and histopathology are consistent with a true prevalence of infection in the slaughter population of up to 11%.
Furthermore, even if the sheep tested within the healthy slaughter population are thought to be representative of the slaughtered population, this does not equate to the standing population.
For example, in Great Britain the healthy slaughter population has been used to estimate the prevalence in the national flock [ 37, 44].
The different profile for the age of CS cases in the healthy slaughter population most probably reflects a different underlying age distribution.
In other genotypes of sheep this latent period would be expected to be longer, perhaps lasting years after natural infection and represents a considerable challenge for the detection of pre-clinically infected sheep in the general or slaughter population.
There was time-dependent variability of the CS prevalence in five countries, including Cyprus for TSE positives in the healthy slaughter population only, and Ireland in the fallen stock only.
Even if we accept this practical constraint, we can still take advantage of the fact that in many countries a proportion of the total slaughter population consists of breeding stock and dairy cows that are culled at >7 years of age, and animals that go directly to rendering plants or die "on farm" further increase this number.
Baseline risks, those of the slaughtered populations across Europe, and country-specific covariates, available from the European Commission Report, were inputted in the model to explain the heterogeneity.
We have assessed the relationship of the logOR (FS/AS) with the baseline risk (AS) to account for the potential variability in the risks of the slaughtered populations between countries on the overall heterogeneity.
