In situations where maintaining flo

In situations where maintaining flocks free of M. synoviae is not feasible (e.g. at a multi-age
commercial layer farm) vaccination is a practical option for infection control. The commercially available live attenuated vaccine contains the temperature sensitive (ts+) MS-H strain
(Vaxsafe MS-H, Bioproperties Pty. Ltd. Australia), and it is used in many countries [6,7]. To
perform control and eradication programs, molecular typing techniques have to be able to differentiate the ts+ MS-H vaccine strain from field isolates. It is also important to examine
whether the vaccine strain has successfully colonized the respiratory mucosa and thus produced an efficient immune response against wild-type strains. The sequence analysis of the
vlhA gene was widely used to differentiate the MS-H vaccine strain from clinical isolates [8–
11]. Unfortunately, it turned out that the vlhA gene sequence profile of the MS-H vaccine strain
is not unique and several Australian and European field strains share the same vlhA gene
sequence [9,12]