Inter-laboratory ring trials to evaluate serological methods for dourine diagnosis

To evaluate the reproducibility of routine serological methods to detect Trypanosoma equiperdum antibodies in equine sera, two inter-laboratory ring trials were organized involving 22 European and 4 non-European reference laboratories for dourine. The serological methods were the complement fixation test (CFT; 25 laboratories) and the indirect fluorescent antibody test (IFAT; 4 laboratories). Three of the laboratories applied both these methods. The sample panels were composed of sera that were negative, positive or suspected for dourine. Of the negative sera, one was from a donkey naturally infected with Trypanosoma evansi. This study confirmed the reliability of CFT and highlighted its inter-laboratory reproducibility for known T. equiperdum positive and negative sera. However the reproducibility was less good for sera positive for T. evansi or of unknown status, e.i. nine out of 22 laboratories observed a false-positive result with the T. evansi-positive serum, whether by CFT or IFAT. This interesting result suggests that the specificity of dourine serodiagnosis may be improved by standardizing the critical reagents, including antigens and by developing a standard T. equiperdum serum which could be used calibrate test systems across multiple laboratories. Trial data confirmed seropositivity in one of the three horses suspected of dourine. It may be beneficial to generalize the use of a suitable low-titer serum control, derived from a standard serum in order to standardize the method's detection limit.