Immune protection conferred by three commonly used commercial live attenuated vaccines against the prevalent local strains of avian infectious bronchitis virus in southern China

FAN, Wen-Sheng; LI, He-Ming; HE, Yi-Ning; TANG, Ning; ZHANG, Li-Hua; WANG, Hai-Yong; ZHONG, Lian; CHEN, Jian-Cai; WEI, Tian-Chao; HUANG, Teng; MO, Mei-Lan; WEI, Ping

At 2-5 dpc, there were birds in the vaccinated groups exhibited gasping, coughing, sneezing, tracheal rale and nasal discharge and some looked depressed with anorexia, ruffled feathers, dry claw and wet droppings. Some even exhibited severe respiratory distress and eventually died. And all the birds in the non-vaccinated group showed much more severe clinical signs than those in the vaccinated groups. In the necropsy at 5 dpc, the kidneys of the birds challenged with GX-YL5 strain were swollen and pale, and showed a white sludge of urate deposition, and some birds showed trachitis with exudates. The birds challenged with GX-GL11079 and GX-NN09032 strains exhibited more exudates in the trachea. No clinical signs or gross lesions were observed in any birds in the blank control group. The immune protection rates of each group against the challenge The morbidity, mortality and protective rate of the experiment groups at 5 dpc were summarized in Table 1 . The results showed that the protection rates of H120, 4/91 and LDT3-A vaccines against the infection of GX-YL5, GX-GL11079 and GX-NN09032 strains were 41.7-58.3%, 75.0-83.7% and 66.7-75.0%, respectively. The protection rate of the 4/91 group against the challenge of GX-NN09032 strain was the highest (83.7%). As expected, no protection was observed in the non-vaccinated group. No morbidity and mortality were observed in any birds in the blank control group.