Efficacy of Live Infectious Bronchitis Vaccine Programs against Infection by QX-Like Strain of Infectious Bronchitis Virus

The aim of this study was to evaluate the efficacy of live infectious bronchitis (TB) vaccine programs against infection by a QX-like strain of the IB virus isolated in Thailand. The experimental groups were divided into 5 groups. Group 1 broilers were administered with Poulvac TB QX-like at 1 day old. Group 2 broilers were administered with Poulvac TB QX-like at 1 and 14 days old. Group 3 broilers were administered with Nobilis TB H120 and Poulvac TB QX-like at 1 and 14 days old, respectively. Group 4 broilers were administered with Nobilis TB H120 and Nobilis TB 4-91 at 1 and 14 days old, respectively. Group 5 served as a positive control group. All groups were challenged with IBV THA80151 at a concentration of 10(5.62) ELD50/0.1 ml. Tracheal rales, mortality rate, body weight, ciliostasis, histopathological lesions, immunological responses and virus isolations were monitored. Although different vaccination programs were used in this study, all the vaccinated groups demonstrated protection against damage after the challenge with live TB QX-like virus. The vaccines were able to decrease the tracheal rales, ciliary activity and histological lesion scores in the vaccinated groups compared with the positive control group but the vaccination programs could not prevent infection because TB QX-like virus was still re-isolated from some infected organs. The booster vaccine with the heterologous strain was able to increase the cross protection of IBV QX-like challenge.