Document details for 'Diagnostic accuracy of PCR for Jaagsiekte sheep retrovirus using field data from 125 Scottish sheep flocks'

Authors Lewis, F.I., Brulisauer, F., Cousens, C., McKendrick, I.J. and Gunn, G.J.
Publication details Veterinary Journal 187, 104-108.
Keywords Jaagsiekte sheep retrovirus; Diagnostic test validation; PCR
Abstract Using a representative sample of the Scottish sheep flock comprising 125 distinct flocks, the sensitivity and specificity of PCR for Jaagsiekte sheep retrovirus (JSRV) was estimated. By combining and adapting existing methods, the characteristics of the diagnostic test were estimated in the absence of a gold standard reference test using repeated laboratory replicates. As the results of replicates within the same animal cannot be considered to be independent, the performance of the PCR was calculated at individual replicate level. The median diagnostic specificity of the PCR when applied to individual animals drawn from the Scottish flock was estimated to be 0.997 (95% CI 0.996-0.999), whereas the median sensitivity was 0.107 (95% CI 0.077-0.152). Considering the diagnostic test as comprising three replicates, where a positive result on any one or more replicates results in a positive test, the median sensitivity increased to 0.279. Reasons for the low observed sensitivity were explored by comparing the performance of the test as a function of the concentration of target DNA using spiked positive controls with known concentration of the target DNA. The median sensitivity of the test when used with positive samples with a mean concentration of 1.0 target DNA sequence per 25 μL was estimated to be 0.160. This suggests that the PCR has a high true (analytical) sensitivity exploiting its technical potential to a high degree and that the low observed (diagnostic) sensitivity in individual samples is due to low concentrations of target DNA in the blood of clinically healthy animals.
Last updated 2012-03-22

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