Interlaboratory trial on TSE rapid tests for the control of the Italian scrapie surveillance network

Abstract

Scrapie, a neurodegenerative disease of sheep and goats and one of several transmissible spongiform encephalopathies (TSEs) has been subject to mandatory active surveillance in EU through rapid testing since 2002. Regulation EC/999/2001 on TSE surveillance requires that each Member State's National Reference Laboratory for TSE periodically verifies diagnostic standards and methods by comparative testing. In 2007 the Italian Reference Centre carried out the first ring trial for classical scrapie on a set of 21 negative and 9 positive homogenated brainstems, the latter consisting of three replicates of an ARQ/ARQ scrapie positive sample diluted 1:10, 1:20 and 1:50. The purpose of the study was to verify the interlaboratory agreement in term of Cohen's kappa (k) of the rapid systems currently used by the 25 national rapid test laboratories (RTLs) [laboratories: Biorad TeSeE (17 laboratories), Enfer TSE version 2.0 (4 laboratories), Idexx Herd chek BSE-scrapie antigen kit (3 laboratories) and Prionics check LIA SR (1 laboratory)]. Our results show that the agreement among the laboratories using the same rapid test varied between 0.84 and 1, while the estimated overall agreement among the 25 laboratories was very good (k-combined=0.87, 95% confidence interval 0.85-0.89). Nevertheless, as regards differences in analytical sensitivity among the rapid tests in use, under-recognition of pre-clinical scrapie cases by lower performing systems must be expected.

Transmissible spongiform encephalopathy in goats: is PrP rapid test sensitivity affected by genotype?

“…This general ranking is supported by the data from other studies in both sheep and goats. 5,21,24,25 Our results confirm that the stage of the incubation period at which an infected animal is tested determines the amount of PrP Sc available for detection and consequently the likelihood that any rapid test will correctly identify an infected animal. [1][2][3]8,19,27,29,30,33 A considerable proportion of preclinical animals are likely to be missed in large-scale surveillance.…”

“…The IDEXX SR ( A ) and the IDEXX BOV ( B ) tests both performed well regardless of the host genotype, and only failed to detect disease-specific levels of PrP in the 2 animals that were preclinical intercurrent deaths. Bio-Rad SG ( C ) and Bio-Rad TeSeE ( D ) data 25 are shown for comparison. Filled circles indicate positive test results from transmissible spongiform encephalopathy (TSE)-positive animals; open circles indicate TSE-negative test results derived from TSE-negative animals; half-filled circles indicate TSE-negative test results associated with TSE-positive animals.…”

“…This general ranking is supported by the data from other studies in both sheep and goats. 5,21,24,25…”

Atypical Transmissible Spongiform Encephalopathies in Ruminants: A Challenge for Disease Surveillance and Control

“…These procedures are indispensible, because false-negative and false-positive test results are highly undesirable. By these means, TSE screening tests became exemplary for the validation and control of laboratory diagnostic procedures in the veterinary field 129,152,153 . However, because of the lack of reference materials, these measures do not specifically address the performance of identifying atypical TSE cases in most countries.…”