“…The MD vaccine viruses are considered one of the most potent vectors for polyvalent live vaccines expressing foreign antigens related to vaccineinduced immunity against poultry diseases for the following reasons. (i) The viruses induce lifetime protection against MD with just one vaccination (39), (ii) the viruses have a natural host range limited to avian species, and therefore, the vectors would be safe for other domestic animals and people working in the poultry industry, and (iii) techniques for generating recombinant MDVs have been well established (45,49). Among the vaccine viruses, HVT has been used worldwide both as live vaccine and polyvalent vaccine vector (13,17,28,29,41,42,53).…”