Novel variant strains of infectious bursal disease virus isolated in China.

Infectious bursal disease (IBD) is one of the most important immunosuppressive diseases that seriously threaten poultry farming and food safety worldwide. The variant strain of infectious bursal disease virus (IBDV) has been greatly neglected for more than 30 years. Recently, the subclinical infection of suspected IBD, causing considerable economic losses, occurred in the main chicken-farming regions of China. Through RT-PCR, sequencing, and phylogenic analyses, novel variant IBDVs were first identified in six provinces of eastern China. Immunological detection further confirmed the antigenic variation of the Chinese variant IBDVs. The Chinese IBDV variants were obviously different from the American IBDV variants, with less than a 97.7% (VP1) or 98.7% (VP2) amino acid sequence identity. Animal experiments further confirmed the serious threat of the variant IBDVs to chickens, demonstrating irreversible damage to the central immune organ, obvious immunosuppression, and growth retardation. This study not only identified the pandemic nature of the novel variant IBDVs for the first time but also discovered the distinct molecular epidemiological characteristics of these viruses, which will contribute more to the control of the disease.