Molecular epidemiology of infectious bursal disease viruses isolated from Southern China during the years 2000-2010

We performed a molecular epidemiology study of infectious bursal disease virus (IBDV) from six provinces in southern China by analyzing IBDVs isolated during the years 2000-2010. Sequence analysis of hypervariable regions of the VP2 gene (vVP2) in the genome of these isolates revealed that the majority of these viruses (45/59) were characterized as vv (very virulent) IBDV genotype, 12 out of 59 isolates were avirulent IBDV genotype and two from Guangxi were intermediate IBDV genotype. Phylogenetic analysis revealed that 45 vvIBDV genotype isolates have divided into five groups, all displaying strong divergence from the currently used vaccine strains. In all isolates, 14 non-critical amino acid substitutions were found in vVP2. The isolates from 2006 to 2010 had more substitutions (11 sites) than the isolates from 2000 to 2005 (7 sites). This study demonstrates that there were different genotypes of IBDV prevailing in six provinces of southern China. The mutations in vVP2 were common, which might be one of the reasons for the evolution of the IBDVs. Therefore, in regards to IBDV prevention, it is vital to have continuous monitoring of the genetic variability (long-term tracking of viral evolution) to provide optimal protection against IBDV.