The Thai Journal of Veterinary Medicine


The present study was designed to evaluate the protection induced by different vaccination programs against Thai QX-like infectious bronchitis virus (IBV). The chickens were divided into 5 groups, 16 chickens in each. Groups 1-4 were vaccinated with different regimes of vaccination program against IBV. Groups 5 did not receive IBV vaccine and served as a positive control group. At 1 day old, the chickens in groups 2 and 3 were vaccinated with QX vaccine whereas the chickens in group 4 were vaccinated with H120 vaccine. At 14 days old, revaccination was performed in group 2 with QX vaccine whereas groups 3 and 4 were vaccinated with a combined vaccine, Newcastle disease virus strain B1 combined with IB strain Massachusetts (Mass) and Connecticut (Conn) (B1/Mass/Conn). The chickens in group 1 were only vaccinated with QX vaccine at 7 days old. At 28 days old, the chickens in groups 1-5 were individually challenged with 104 EID50 of Thai QX-like IBV (isolate THA80151). The protection was evaluated at 7 days post-inoculation. The results showed that the clinical signs of all vaccinated groups were lower (p<0.05) than those of the positive control group. Virus detection in the tracheas and the histopathological lesion score of the tracheas and kidneys of the vaccinated groups were not significantly different (p>0.05) from those of the positive control group. The body weights of the vaccinated groups excluding group 3 were not significantly different (p>0.05) from that of the positive control group. It is suggested that all of the vaccination programs used in this study offered clinical protection against Thai QX-like IBV, but they did not provide sufficient protection against virus infection and histopathological lesions in the tracheas and kidneys.

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