Characterization of antigenic variant infectious bursal disease virus strains identified in South Korea

Abstract

Infectious bursal disease (IBD) is one of the most important immunosuppressive diseases of young chickens, causing considerable economic losses to the poultry industry. More than 30 years ago, an antigenic variant (av) pathotype of the IBD virus (IBDV) was reported to originate in, and subsequently spread among, poultry farms in the USA. Recently, a novel avIBDV lineage was identified in China and was shown to exhibit clear differences in its pathogenicity as well as molecular characteristics compared with the previously isolated variant strains. In this study, we conducted a passive surveillance of chicken carcasses submitted to our research division from June-December 2019, and detected the IBDV strains by reverse transcription PCR. Five avIBDV strains were isolated, and their pathogenicity was determined by necropsy and molecular analysis. Additionally, a coinfection field case involving an avIBDV strain and a very virulent IBDV (vvIBDV) strain was identified. Multiple sequence alignment and phylogenetic analysis of partial viral protein 1 (VP1) and hypervariable region (hv) VP2 genes revealed that those strains originated from two different avIBDV lineages. The co-occurrence of two subgroups of avIBDVs in South Korea confirms for the first time the evolution of antigenic variant IBDV strains, and highlights the urgency for the development of new strategies for IBDV intervention in South Korea. RESEARCH HIGHLIGHTS:. Five avIBDV strains were identified in South Korea by passive surveillance test in 2019.. A coinfection between two IBDV strains from different genogroups was reported in a field case.. By phylogenetic analysis, Korean avIBDVs belonged to two distinct lineages of antigenic variant genogroup.

Identification and Pathogenicity Evaluation of a Novel Reassortant Infectious Bursal Disease Virus (Genotype A2dB3)

“…The phylogenetic trees based on the nucleotide sequences of the polyprotein in Segment A showed that Serotype I strain contained four previously described genogroups: A1 (cIBDV), A2 (VarIBDV), A3 (vvIBDV), and A8 (aIBDV) [ 8 ]. Genogroup A2 included lineages A2a/b/c (early variant IBDV) and A2d (nVarIBDV) [ 8 , 18 ]. The IBDV-JS19-14701 strain was clustered with SHG19 [ 16 ], which is a representative strain of nVarIBDV (A2d) ( Figure 1 a).…”

“…The HLJ0504-like IBDVs (A3B3) are the main prevalent strains with high pathogenicity, which have been threatening the poultry farming in China for nearly 30 years [ 9 , 10 , 11 , 12 ]. Such type of IBDVs have also been circulating in the neighboring countries including Pakistan [ 11 , 14 ], India [ 15 ], Bangladesh [ 38 ], Thailand, Vietnam [ 39 ], and Korea [ 18 ], and were also reported in Venezuela [ 30 ]. Recently, the widespread of nVarIBDV (A2dB1) was discovered in China [ 16 , 40 ] and also reported in Japan [ 17 ], Korea [ 18 ], and Malaysia [ 19 ] in succession.…”

“…Such type of IBDVs have also been circulating in the neighboring countries including Pakistan [ 11 , 14 ], India [ 15 ], Bangladesh [ 38 ], Thailand, Vietnam [ 39 ], and Korea [ 18 ], and were also reported in Venezuela [ 30 ]. Recently, the widespread of nVarIBDV (A2dB1) was discovered in China [ 16 , 40 ] and also reported in Japan [ 17 ], Korea [ 18 ], and Malaysia [ 19 ] in succession. The damage caused by nVarIBDV to the poultry industry has been well documented that nVarIBDV can cause severe bursal lesions and immunosuppression [ 16 , 41 , 42 ].…”

“…In addition, one virulent IBDV named HLJ0504-like strains (A3B3) are circulating in China [9][10][11][12][13], Pakistan [11,14], and India [15]. Recently, the epidemics caused by novel variant IBDV (nVarIBDV) were successively reported in China [16], Japan [17], Korea [18] and Malaysia [19]. The nVarIBDV strains were classified as Genotype A2dB1, which were genetically different from the early variant IBDV originally reported in America [8,18].…”

“…Recently, the epidemics caused by novel variant IBDV (nVarIBDV) were successively reported in China [ 16 ], Japan [ 17 ], Korea [ 18 ] and Malaysia [ 19 ]. The nVarIBDV strains were classified as Genotype A2dB1, which were genetically different from the early variant IBDV originally reported in America [ 8 , 18 ].…”