Effect of infectious bronchitis and Newcastle disease vaccines on experimental avian influenza infection (H9N2) in broiler chickens

Despite the fact that H9N2 avian influenza virus (AIV) is considered a low-pathogenic agent, frequent outbreaks of this subtype have caused high mortality and economic losses in poultry farms around the world including Iran. Coinfection with a respiratory pathogen or environmental factors may explain the exacerbation of H9N2 AIV infection. In this study, the role of infectious bronchitis (IB) vaccines (H120 and 4/91) and Newcastle disease (ND) vaccines (B1 and LaSota) on experimental H9N2 AIV infection was investigated in 180 broiler chickens allotted into 6 groups (n=30). At the age of 18 days, groups 3 and 4 received H120 and 4/91 infectious bronchitis live vaccines (IBLVs) and groups 5 and 6 received B1 and LaSota Newcastle disease live vaccines (NDLVs), respectively. At the age of 20 days, all birds in the experimental groups except the negative control group (group 1), were inoculated intra-nasally with H9N2 AIV. After the inoculation, clinical signs, gross and microscopic lesions, and viral detection were examined. The results of this study revealed that clinical signs, gross and microscopic lesions were more severe in the AIV challenged groups which had been previously vaccinated with IB vaccines. In addition, AI viral RNA from tracheal and faecal samples in IB vaccinated birds were recovered at a higher rate. Moreover, in the 4/91 IB vaccinated group, the AI virus shedding period was longer than the other challenged groups. In conclusion, infectious bronchitis live vaccines (IBLVs) exacerbated the H9N2 AIV infection; also, 4/91 IBLV extended AI virus shedding period and increased the recovery rate of AI virus from feaces. However, the coinfection of Newcastle disease live vaccines (NDLVs) had no considerable adverse effects on AIV infection in broiler chickens.