Acute infectious bursal disease in poultry: Immunological and molecular basis of antigenicity of a highly virulent strain

Abstract

This study has confirmed, by the use of immunological and molecular tools, that the recent failures of vaccination against infectious bursal disease (IBD) encountered in Europe were not related to antigenic variation, but to increased virulence of the circulating IBD virus strains. Neutralizing monoclonal antibodies (Mabs) showed that the vaccines of intermediate virulence and the pathogenic strain 849VB had a similar pattern of reactivity in ss neutralization tests. Four distinct epitopes could be defined in seroneutralization and addition ELISA tests. All neutralizing Mabs bound to the structural VP2 protein only in its native form. Moreover, Mabs which did not neutralize some strains precipitated well the VP2 protein from extracts of cells infected with the same virus. This suggests that slight changes in the conformation of the epitope were sufficient to allow the virus to escape to neutralization. VP2 sequencing results confirmed that the neutralizing epitopes are clustered in the variable domain which is highly hydrophobic and flanked by two major hy-drophilic peaks. Three potential 'minor' antigenic sites were identified within the hydrophobic region. Comparison of the VP2 sequence of 849VB strain with other highly virulent isolates showed that they are close together and clearly distinct from 'classical' strains. Moreover, sequencing of IBD vaccines revealed that some of them had not been cloned.

Phylogenetic evidence for homologous recombination within the family Birnaviridae

“…Potential recombinant 849VB is a European vvIBDV that was isolated from Belgium in 1987 ( Van den Berg et al, 1996). It is geographically and temporally consistent with its closest A-VV parental strain, D6948, which was isolated from the Netherlands in 1989.…”

“…In the cases of Ab and 20Gld, the sequences were obtained using a direct PCR sequencing strategy (Blake et al, 2001;Romero-Brey et al, 2004). In addition, for 849VB, six independent clones were sequenced although the amplicons were cloned before sequencing (Van den Berg et al, 1996). Therefore, these three potential recombinants are not likely to have been derived in vitro.…”

Genetic characterization of South American infectious bursal disease virus reveals the existence of a distinct worldwide-spread genetic lineage

“…These vvIBDVs were antigenically similar to the cIBDVs, but they were able to breakthrough the existing level of maternally derived protection (van den Berg et al, 1996).…”

Sequence Comparison of the VP2 Variable Region of Infectious Bursal Disease Virus Isolates from Vietnam.

“…Field strains: Twenty-three field bursa samples were collected from outbreaks of IBD occurred in Vietnam in D00869 [3]; STC, accession D00499 [15]; Cu-1, accession D00867 [3]; PBG98, accession D00868 [3]; Variant A, accession M64285 [18]; Variant E, accession D10065 [10]; 849VB, accession X95883 [28]; UK661, accession X92760 [6]; OKYM, accession D49706 [31]; DV86, accession D16675; HK46, accession AF051838; OH, accession M66722 [16]; 23/82, accession Z21971 [26].…”