Preliminary comparative analysis of the genomes of selected field reisolates of the Mycoplasma synoviae vaccine strain MS-H reveals both stable and unstable mutations after passage in vivo.

These results suggest that the majority of the MS-H mutations are stable after passage in vaccinated chickens. Characterisation of stable mutations found in MS-H could be utilised to develop rapid diagnostic techniques for differentiation of vaccine from field strains or ts- MS-H reisolates.