Performance and trends of the results of the Interlaboratory Trials held between 2002-2017 for the serological tests employed for the diagnosis of Equine Infectious Anemia

Abstract

The aim of this paper is to analyze the trend of the Interlaboratory Comparison (IC) for serological techniques used in the diagnosis of Equine Infectious Anemia (EIA), organized by the National Reference Centre for Equine Infectious Anemia in the years 2002-2017. The participation of numerous laboratories at national level and the long time interval considered gives greater value to the data obtained. The increase in the samples to be tested for the legislative provisions, and the need to participate to the IC with a satisfactory outcome for the purpose of accreditation, has made this tool important for verifying the technical competence of the laboratories. Overall, even if the system has an acceptable sensitivity, the ELISA presented higher concordance levels and better reproducibility than the agar gel immunodiffusion (AGID). The implementation, since 2007, of the regular serological testing for EIA requested the use of highly sensitive techniques, such as the ELISA; this assay indeed is capable of detecting weak positive sera that, in an advanced stage of eradication, constitutes the majority of the positive samples and are difficult to diagnose in AGID, while those with a strongly positive reaction have been already recruited and removed through previous surveillance activities. The high number of laboratories that immediately participated in the IC for ELISA reflects its diagnostic value owing to its high sensitivity, underlined by the reduced percentage of errors obtained for the positive sera. This makes it an effective tool, in support of the eradication of infection to be applied during the screening phase of the national surveillance program, to recruit sera not detected in AGID.