RT Journal Article SR Electronic(1) A1 Nouën, Cyril Le A1 Rivallan, Gaëlle A1 Toquin, Didier A1 Darlu, Pierre A1 Morin, Yannick A1 Beven, Véronique A1 de Boisseson, Claire A1 Cazaban, Christophe A1 Comte, Sylvain A1 Gardin, Yannick A1 Eterradossi, NicolasYR 2006 T1 Very virulent infectious bursal disease virus: reduced pathogenicity in a rare natural segment-B-reassorted isolate JF Journal of General Virology, VO 87 IS 1 SP 209 OP 216 DO https://doi.org/10.1099/vir.0.81184-0 PB Microbiology Society, SN 1465-2099, AB 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., UL https://www.microbiologyresearch.org/content/journal/jgv/10.1099/vir.0.81184-0