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

Seven-day-old SPF birds were randomly divided into five groups, which were named as H120 group, 4/91 group, LDT3-A group, non-vaccinated group and blank control group, respectively. There were 12 birds in the blank control group and 36 birds in the other four groups. Birds in the groups of H120, 4/91 and LDT3-A were vaccinated by eye and nose drop with H120, 4/91 and LDT3-A attenuated vaccines, respectively, at the manufacturer's recommended dose. Birds in the non-vaccinated group were treated with sterile phosphate-buffered saline in the same manner and those in the blank control group received nothing. Blood samples were collected from 10 birds in each group prior to inoculation (0 day) and at 7, 14 and 21 post-inoculation (dpi) of the vaccines for detection of IBV-specific antibody and quantity analysis of CD4 + and CD8 + T lymphocytes. At 21 dpi birds in the H120, 4/91, LDT3-A and non-vaccinated groups were divided randomly into three groups of 12 birds each and challenged via eye and nose drop with 0.2 ml of 10 4 TOC-ID 50 of IBV GX-YL5, GX-GL11079 and GX-NN09032 strains, respectively. Birds in the blank control group received no challenge virus. Clinical signs were observed and recorded daily. At 5 days post-challenge (dpc), the birds in each group were humanely killed and necropsied. The trachea and kidney samples were collected from each bird aseptically for the detection of viral loads. The dead birds were also necropsied to confirm the infection of IBV.