Serological study reveal different antigenic IBDV strains prevalent in southern China during the years 2000-2017 and also the antigenic differences between the field strains and the commonly used vaccine strains.

The aim of this study was to determine the antigenic relatedness of Infectious Bursal Disease Viruses (IBDVs) in the field in southern China during the period 2000-2017, as well as the antigenic relationship between the field strains and the most commonly used vaccine strains by using a virus neutralization (VN) test in vitro. The antigenic relatedness (R) value and the difference in VN titers were analyzed, and the antigenic index based on the sequences of the hypervariable region of VP2 (vVP2) of the strains was further evaluated. As a result, the R value of representative field strains showed that there were three subtypes present in the field strains examined, with 7 strains belonging to subtype 1, while strains BH11 and JS7 belonged to subtype 2 and subtype 3, respectively. The commonly used vaccine strains B87 and FW2512 belonged to subtype 1. The analysis of the VN titer differences revealed that all the 136 field strains were classified into subtype 1, except BH11 and JS7. All the field strains in subtype 1 have been divided into at least 5 subgroups, suggesting the antigenic diversity among these strains. The antigenic index based on IBDV-VP2 sequences further confirmed the antigenic differences between the three subtype strains and also the antigenic diversity among the subtype 1. The results demonstrated the antigenic diversity of field IBDVs in southern China during the years 2000-2017 and the antigenic differences between the field strains and the commonly used vaccine strains. This would indicate that the commonly used vaccines are only partially effective. These results enhance our understanding of IBDV genetic evolution and should help to develop more effective vaccines for the control of this disease in the future.