Identification of prion protein genotype in sheep: 11 years of proficiency tests in Italy

Abstract

Scrapie of sheep belongs to a group of fatal neurodegenerative diseases known as prion diseases. Scrapie is a naturally transmissible disease and sheep susceptibility is highly dependent on the host prion protein (PrP) genotype. On this basis, the European Union has established management strategies of scrapie in sheep population, to be achieved by an ad hoc breeding programme to increase the genetic resistance of the ovine population and by selective culling, both based upon the PrP genotyping. The Istituto Superiore di Sanita, appointed by the Italian Ministry of Health as the Reference Laboratory for PrP genotyping, has since 2005 organised proficiency tests (PTs) for sheep PrP genotype identification. The PT aims at assessing the accuracy of the genetic analysis performed by the laboratories involved in official control at national level. From 2005 to 2016, 12 laboratories on average participated to nine PT rounds. The overall analytical performance was satisfactory with few laboratories reporting errors in PrP genotype identification. A total of 22 errors including sixteen analytical and six formal errors were identified out of 2650 results reported (0.8 %). The number of laboratories reporting 100 % correct results increased over the years although no statistical trend could be observed. The low number of laboratories failing the PT revealed an overall good technical capability and skills of laboratories and technicians in performing the genetic analysis. This is highly important since the availability of an efficient laboratory network is crucial for the implementation and management of scrapie control plan at national level.