European ring test on the differentiation of wild-type Mycoplasma synoviae and the MS-H vaccine strains in clinical samples

The control and prevention of Mycoplasma (M.) synoviae infections have been significantly improved by the use of the MS-H live vaccine strain. This vaccine has been used globally for decades; therefore, many technical approaches have been published or commercialized for the differentiation of MS-H from field strains. However, key problems have been identified related to DIVA (differentiating infected from vaccinated animals) testing and monitoring of vaccination in many European laboratories and poultry farms. To address these concerns, the reliability of protocols for the differentiation of the MS-H vaccine and wild-type M. synoviae strains from clinical samples was assessed with the blind participation of 16 European laboratories using various techniques. Three pools of samples were sent to each laboratory containing equal amounts of either just MS-H vaccine or a field strain, or the mix of the two strains. The results highlight the challenges in live vaccine strain differentiation, as only 84.4 % (n = 38/45) of the samples were correctly identified. The present study also revealed a variability in the specificity between laboratories using the same technique, which indicates the influence of the operator and differences in the evaluation of raw data also. Sample pools containing both strains showed the highest failure rate in strain differentiation. Therefore, results obtained from laboratory testing should ideally be confirmed using an alternative appropriate technique and interpreted in consultation with the responsible veterinarian, taking into account the clinical history before making decisions with potentially high economic impact.