Genomic Characterization of an Emergent Cross-Border Recombinant Duck Plague Virus With High Pathogenicity and Reduced Vaccine Efficacy in Guangxi, China.

Duck plague virus (DPV) is a major pathogen causing recurrent outbreaks in waterfowl. This study reports the comprehensive characterization of a novel DPV strain, designated GXGG240520, isolated from clinically diseased ducks in Guangxi, China. The strain was confirmed as a virulent DPV by PCR targeting the UL2 gene (1002 bp) and exclusion of other common duck pathogens. In pathogenicity tests, ducks challenged with GXGG240520 exhibited severe clinical signs including anorexia, diarrhea, and hemorrhagic stools, with mortality concentrated between 5 and 9 days postchallenge and a final survival rate of only 10%. Pathological examination revealed hemorrhagic lesions in multiple organs and atrophy of immune organs such as the bursa of Fabricius and thymus. Viral load was highest in the thymus and lowest in the heart. Notably, challenge protection experiments demonstrated that the currently available vaccine (C-KCE strain) provided only limited protection, with 60% mortality in vaccinated ducks, indicating reduced vaccine efficacy capability. Whole-genome sequencing revealed a genome length of 162,188 bp with 78 predicted open reading frames (ORFs). Comparative genomic analysis identified 40 amino acid deletions and mutations across 26 ORFs. Homologous recombination analysis confirmed that GXGG240520 originated from cross-border recombination between the Chinese virulent strain CHv (major parent) and the Bangladeshi strain YLBRDP 11 (minor parent). Furthermore, structure prediction of the UL47 protein revealed marked differences in α-helix and β-sheet organization compared to both parental strains. This recombinant strain with high pathogenicity and reduced vaccine efficacy potential poses a significant challenge to current DPV control strategies.