Development and evaluation of novel recombinant adenovirus-based vaccine candidates for infectious bronchitis virus and <i>Mycoplasma gallisepticum</i> in chickens

<p>Avian infectious bronchitis caused by the infectious bronchitis virus (IBV), and mycoplasmosis caused by <i>Mycoplasma gallisepticum</i> (MG) are two major respiratory diseases in chickens that have resulted in severe economic losses in the poultry industry. We constructed a recombinant adenovirus that simultaneously expresses the S1 spike glycoprotein of IBV and the TM-1 protein of MG (pBH-S1-TM-1-EGFP). For comparison, we constructed two recombinant adenoviruses (pBH-S1-EGFP and pBH-TM-1-EGFP) that express either the S1 spike glycoprotein or the TM-1 protein alone. The protective efficacy of these three vaccine constructs against challenge with IBV and/or MG was evaluated in specific pathogen free chickens. Groups of seven-day-old specific pathogen free chicks were immunized twice, two weeks apart, via the oculonasal route with the pBH-S1-TM-1-EGFP, pBH-S1-EGFP, or pBH-TM-1-EGFP vaccine candidates or the commercial attenuated infectious bronchitis vaccine strain H52 and MG vaccine strain F-36 (positive controls), and challenged with virulent IBV or MG two weeks later. Interestingly, by days 7 and 14 after the booster immunization, pBH-S1-TM-1-EGFP-induced antibody titre was significantly higher (<i>P </i>< 0.01) compared to attenuated commercial IBV vaccine; however, there was no significant difference between the pBH-S1-TM-1-EGFP and attenuated commercial MG vaccine groups (<i>P </i>> 0.05). The clinical signs, the gross, and histopathological lesions scores of the adenovirus vaccine constructs were not significantly different from that of the attenuated commercial IBV or MG vaccines (positive controls) (<i>P </i>> 0.05). These results demonstrate the potential of the bivalent pBH-S1-TM-1-EGFP adenovirus construct as a combination vaccine against IB and mycoplasmosis.</p>