Evaluation of Three Rapid Diagnostic Tests Used in Bovine Spongiform Encephalopathy Monitoring in Italy

Abstract

Abstract. In 2001, a compulsory active surveillance system was started in the European Union to assess the prevalence of bovine spongiform encephalopathy (BSE) in the cattle population. The aim of the current study was to report on the field performances of 3 rapid tests: a Western blot (WB), a chemiluminescence enzymelinked immunosorbent assay (ELISA), and an immunochromatographic assay, routinely used at 3 laboratories of the Istituto Zooprofilattico Sperimentale of Lombardia and Emilia Romagna, over 8 years of BSE monitoring activity. A total of 2,802,866 samples from slaughtered animals and 202,453 samples from fallen stock were tested by 1 of 3 tests. Positive results of the rapid tests were confirmed by histopathological examination, immunohistochemistry, and confirmatory WB. The field performances (i.e., initial reactive and false-positive rates) and practical aspects regarding resources and applicability of the tests to high-throughput routine testing laboratories were evaluated. The 3 tests proved to be reliable tools when applied to slaughtered samples, showing no or very low false-positive rates (,1 per 100,000 negative samples tested) and low retesting frequencies (0.02-0.26%). When samples from fallen stock were analyzed, performances of the immunochromatographic assay, and especially the chemiluminescence ELISA, were negatively affected, resulting in higher false-positive and retesting rates. On the other hand, both tests are less expensive, much easier to use, provide more rapid results, and adapt well to application in routine laboratories as compared with WB. In the authors' experience, the immunochromatographic assay was a good compromise between performance and convenience.

Effect of autolysis on the specificity of bovine spongiform encephalopathy rapid tests

“…Our results on this test are in accordance with those obtained in that frame, while a recent paper from Carra et all [19] on the evaluation of test A in routine monitoring activity reports a high prevalence of false positive results and frequencies of retested samples on fresh matrix and, with a higher percentage, on poor quality tissues. These data could be referred both to individual batch issues and/or local technical matters.…”

“…To date, there is a little reliable information [19] about the effect autolysis can have on rapid test performance for large-scale throughput samples in terms of number of initially reactive samples and false positive results. To fill this gap, we wanted to determine whether natural autolysis affected the performance of four rapid tests commonly used in the EU for mandatory surveillance of BSE (Prionics ® Check-LIA Test, Enfer TSE Kit version 2.0, Bio-Rad TeSeE Test, IDEXX HerdChek BSE Antigen Test Kit EIA) on negative and autolyzed field samples.…”