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

Three live, attenuated vaccines, H120 (Guangdong Dahuanong Animal Health Products Co., Ltd., Guangzhou, China), 4/91 (MSD Animal Health (Shanghai) Trading Co., Ltd., Shanghai, China) and LDT3-A (QYH Biotech Co., Ltd., Beijing, China) were purchased commercially. Each vaccine was reconstituted according to the manufacturer's instructions. According to our previous description [12, 20] , H120 (Massachusetts serotype) and 4/91 (793B serotype) vaccines were designated as serotype 3 and serotype 5, respectively. The serotype of LDT3-A vaccine was different from Mass-type vaccines and other vaccines used in China [13] . IBV local isolates GX-YL5, GX-GL11079 and GX-NN09032 belonging to serotype 1, 2 and 5, respectively, were isolated from Guangxi, China and were currently the representative dominant serotypes in southern China [10, 18] . GX-YL5, GX-GL11079 and GX-NN09032 strains were propagated in 10-day-old specific pathogen free (SPF) chicken embryos and the 50% tracheal organ culture infection dose (TOC-ID 50 ) was determined as previously described for the quantification of the viruses [12] .