Infectious bursal disease virus suppresses H9N2 avian influenza viral shedding in broiler chickens

Abstract

Infectious bursal disease (Gumboro) virus causes immunosuppression in chickens, increasing their susceptibility to other viral and bacterial diseases and resulting in vaccination failure. In the present study, we investigated the immune-depressing effect of infectious bursal disease virus on H9N2 avian influenza viral infection in commercial broiler chickens. Chickens were divided into four groups. In group A, chickens were inoculated with Gumboro virus at 21 days of age and H9N2 influenza virus 5 days later. Groups B and C only received influenza virus at 26 days of age and Gumboro virus at 21 days, respectively. Chickens in the control group (D) were inoculated with normal saline at the same times.\n\nTissue samples from different organs were collected on days 1, 3, 6, 9, and 12 after H9N2 infection. Macroscopic observation showed bursal disease lesions in groups A and C, including swollen bursa with the presence of gelatinous exudates, hemorrhages in the thigh muscle, edema, and nephritis.\n\nReverse transcription polymerase chain reaction was used to study H9N2 influenza virus dissemination, and quantitative reverse transcription polymerase chain reaction to determine viral genome copy number in different organs. A considerable titer of avian influenza virus was found in the trachea, lungs, cecal tonsils, spleens, and feces of infected chickens. The genome copy number of the virus in the trachea and lungs of group A was significantly higher than that in group B on the first day after inoculation. However, our method did not detect the avian influenza virus genome in group A. In conclusion, we suggest that pre-exposure to Gumboro virus at 3 weeks of age reduces the replication and shedding of H9N2 in broiler chicken.