Concurrent occurrence of infectious bursal disease and respiratory complex caused by infectious bronchitis and avian influenza (H9N2) in broilers

Abstract

Infectious bursal disease (IBD) virus is considered one of the commonest immunosuppressive diseases in chickens. The aim of this study was to investigate the concurrent occurrence of subclinical IBD in respiratory complex infections caused by avian influenza (AI, H9N2) virus and infectious bronchitis (IB) virus in broilers. During this study, 800 tissue samples of the trachea, caecal tonsil, spleen, and bursa of Fabricius and 400 blood samples were collected from 20 respiratory complex infected flocks. Detection of pathogens in the tissue samples was performed by RT-PCR for amplification of the VP2 gene of IBD, HA region of AI, and S1 gene of IB viruses. The amplified products were subjected to nucleotide sequence analysis. Blood samples were also tested for the detection of antibodies against IBV by using ELISA and against AIV via using the HI test. Molecular results showed that the tissue samples were positive for field isolates of subclinical IBD (45%), IB (45%), and AI-H9N2 (25%). Co-infections of IBD and IB (30%), IBD and AI (20%), and IBD, IB, and AI (5%) were also detected. Serological results indicated that subclinical IBD infected flocks had lower (P<0.05) antibody titres against IB and AI. In conclusion, prior exposure of broilers to IBD virus increased the incidence of respiratory complex caused by IBV and AIV in broilers, and vaccination against IBD is inevitable to reduce subclinical IBD to minimise the incidence/severity of respiratory complex diseases via improving immune responses to commonly used vaccines in broilers.