European Inter-Laboratory Proficiency Test for Dourine Antibody Detection Using the Complement Fixation Test

SIMPLE SUMMARY: Dourine is a parasitic disease affecting equids, caused by Trypanosoma equiperdum. Thanks to the implementation of stamping out policies during the 20th century, dourine is now found only in few parts of the world. To prevent the spread of dourine, it is necessary to check that equids are not infected during international movements. In the context of the European Reference Laboratory for equine diseases mandate, our responsibility is to evaluate the capacity of the network of National Reference Laboratories to perform the prescribed test for dourine diagnosis: the complement fixation test. For this purpose, we organised inter-laboratory proficiency tests for dourine diagnosis; these consist of sending panels of samples of known status (containing or not containing anti-T. equiperdum antibodies) to determine whether the laboratories correctly identify the samples. The present article describes the results obtained by national reference laboratories during three sessions of dourine proficiency tests organised in 2015, 2018 and 2022, respectively. These sessions allow the identification of a reagent that should not be used for dourine serodiagnosis and help to improve the performance of the network. This article highlights the importance of inter-laboratory proficiency tests to improve the performance of laboratories and ensure the health safety of equids. ABSTRACT: Dourine is a sexually transmitted parasitic disease affecting equids. Its causative agent is referred to as Trypanosoma equiperdum and the prescribed serodiagnosis method is the complement fixation test (CFT). In the context of our European Reference Laboratory mandate for equine diseases (excluding African horse sickness), we organised dourine CFT inter-laboratory proficiency tests (ILPTs) in 2015, 2018 and 2022 to evaluate the performance of the European Union network of National Reference Laboratories (NRLs) for dourine. ILPT panels were composed of horse sera with or without antibodies against Trypanosoma spp. originating from non-infected, immunised or experimentally infected horses. Twenty-two NRLs participated in at least one of the three sessions. In 2015, 2018 and 2022, the percentage of laboratories obtaining 100% of the expected results was 57, 90 and 80, respectively. These dourine CFT ILPTs showed the benefits of standardising the method’s detection limit and underlined the constant need to evaluate NRLs to improve the network’s performance. These results also argue in favour of the need for a representative bio-bank to improve the representativeness of ILPT samples and to allow the adoption of alternative serological methods for international surveillance of dourine.