Very virulent infectious bursal disease virus: reduced pathogenicity in a rare natural segment-B-reassorted isolate

Abstract

The purpose of this study was to compare the molecular epidemiology of infectious bursal disease virus (IBDV) segments A and B of 50 natural or vaccine IBDV strains that were isolated or produced between 1972 and 2002 in 17 countries from four continents, with phenotypes ranging from attenuated to very virulent (vv). These strains were subjected to sequence and phylogenetic analysis based on partial sequences of genome segments A and B. Although there is co-evolution of the two genome segments (70 % of strains kept the same genetic relatives in the segment A- and B-defined consensus trees), several strains (26 %) were identified with the incongruence length difference test as exhibiting a significantly different phylogenetic relationship depending on which segment was analysed. This suggested that natural reassortment could have occurred. One of the possible naturally occurring reassortant strains, which exhibited a segment A related to the vvIBDV cluster whereas its segment B was not, was thoroughly sequenced (coding sequence of both segments) and submitted to a standardized experimental characterization of its acute pathogenicity. This strain induced significantly less mortality than typical vvIBDVs; however, the mechanisms for this reduced pathogenicity remain unknown, as no significant difference in the bursal lesions, post-infectious antibody response or virus production in the bursa was observed in challenged chickens.

Both Genome Segments Contribute to the Pathogenicity of Very Virulent Infectious Bursal Disease Virus

“…IBDV strain 94432 was originally identified as having both genome segments phylogenetically related to vvIBDVs (41,43) and exhibiting atypical antigenicity (44), most probably based on one amino acid change in the variable antigenic domain of VP2 (43). In this paper we confirm unpublished previous observations that 94432 replicates extensively in the BF but induces only mild clinical signs and does not cause mortality, thus exhibiting a clear discrepancy between its vvIBDV-related genotype and its mildly pathogenic phenotype.…”

“…This observation is consistent with the phylogeny-based hypothesis that both genome segments may be involved in the emergence of vvIBDV (38,39). Recently, this hypothesis was substantiated by the isolation of three naturally occurring segment B-reassorted vvIBDV isolates, all with reduced pathogenicity in chickens (40,41). Another recent experimental study based on reverse genetics demonstrated that several domains of the IBDV polymerase may contribute to virulence (42).…”

“…Viral RNA was extracted from infected BF as described previously (43). The complete nucleotide sequences of segments A and B were determined by sequencing of overlapping reverse transcription-PCR (RT-PCR) products as described previously (41) and by rapid amplification of 5= cDNA ends (5= RACE; Invitrogen) (42,51).…”

Molecular Characterization of Infectious Bursal Disease Virus From Commercial Poultry in Pakistan

“…Leucine (L) to Serine (S) amino acid change is noted in the same sample [31]. Remaining amino acid alterations were mostly conservative in nature [54][55][56][57]. The changes in the hydrophilic regions of the VP2 protein were important as they are indicative of continuous changes going on in viral genome [58][59][60][61][62].…”

Anticorpos contra o vírus da Doença Infecciosa Bursal e detecção do genoma viral em criações de frango de corte e galinhas de quintal no polo avícola da Bahia

“…Nos últimos anos, o uso de técnicas moleculares como a RT-PCR (reação em cadeia da polimerase) tem sido útil na detecção e genotipagem das diferentes cepas de IBDV presentes no campo (NOUEN et al, 2006 ). A população constituída de aves que são criadas para o consumo próprio, conhecidas como galinhas de fundo de quintal, não é beneficiada com o programa de biosseguridade, aplicado nas criações comerciais.…”