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

ABSTRACT

1. Infectious bursal disease virus (IBDV) causes immunosuppression in chickens, increasing their susceptibility to other infectious diseases and resulting in vaccination failure. Here, we investigated the immune-depressing effect of IBDV on H9N2 avian influenza viral infection in the broiler chickens.

2. For this purpose, chickens were divided into four groups. In group A, chickens were inoculated with IBDV at 21 days of age and H9N2 avian influenza virus (AIV) 5 days later. Groups B and C only received AIV at 26 days of age and IBDV at 21 days, respectively. The control group (D) were inoculated with normal saline at the same times. Tissue samples from different organs were collected on the days 1, 3, 6, 9, and 12 after H9N2 infection.

3. Macroscopic observation showed IBD lesions in groups A and C, including swollen bursa with the presence of gelatinous exudates, haemorrhages in the thigh muscle, edema, and nephritis.

4. Reverse Transcription-PCR was used to study H9N2 AIV dissemination, and qRT-PCR to determine viral genome copy number in different organs. A considerable titre of AIV 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. But in the other days post inoculation, RT-PCR did not detect the AIV genome in group A. Although there might have been some immunosuppression in group A, IBDV could interfere with AIV replication in the chickens of this group.

5. In conclusion, we propose that pre-exposure to IBDV at 3 weeks of age reduces the replication and shedding of H9N2 in broiler chicken.

KEYWORDS:

• Broiler chickens
• H9N2 influenza virus
• infectious bursal disease
• qRT-PCR
• shedding

Acknowledgments

The authors would like to thank Mr. Mahdi Asadsangabi, expert virology laboratory technician, and Mitra Mohammadi, master poultry science technician at the school of veterinary medicine, Shiraz University for their assistance that greatly improved the project.

Disclosure statement

No potential conflict of interest was reported by the authors.

Statement of animal rights

The study protocol, including animal sacrifice, was approved by the research ethics committee of Shiraz University. In addition, we followed and adapted the recommendations of the European Council Directive (86/609/EC) of November 24 1986, regarding standards for the protection of animals used for experimental purposes.

Additional information

Funding

This work was supported by the Iran National Science Foundation [grant number: 90006958] and Shiraz University [grant number: 90GCU3M1881].