Antigenic and genetic relationships between European very virulent infectious bursal disease viruses and an early West African isolate

The antigenic and genetic relationships between very virulent (vv) infectious bursal disease viruses (IBDV) from different countries were investigated. Antigenic characterization was performed using an antigen-capture ELISA based on a panel of seven neutralizing monoclonal antibodies (Mabs), which probe at least three VP2-located antigenic domains. All these domains are reactive in the Faragher 52/70 (F52/70) reference strain for European classical serotype 1 IBDV. Genomic characterization was achieved by reverse transcription, amplification and direct sequencing of a genome fragment encoding the VP2 variable domain. Eleven vv isolates from France were compared to the British, Dutch and Belgian UK661, DV86 and 849VB viruses, and to an early vv isolate obtained from the Ivory Coast in 1988. All viruses exhibited antigenic profiles characterized by no binding of Mabs 3 and 4. Lack of binding of Mabs 3 and 4 might thus be helpful for differentiating classical and vvIBDVs. None of the non-French strains resembled the 91168 and 94432 French isolates, which did not bind Mabs 6, 7 or 8. The genetic analysis revealed close relationships between all the European viruses, which differed from one another by no more than 12 nucleotides and 3 amino acids. The African isolate was markedly different, with at least 22 nucleotide and six amino acid differences to all the European viruses, including the F52/70 virus. Phylogenetic analysis based on the neighbour-joining and parsimony methods suggest that the African virus may belong to a genetically distinct lineage of highly pathogenic IBDVs.