Genomic and pathogenic characterization of a highly pathogenic chicken infectious anemia virus strain in China

Chicken infectious anemia virus (CIAV) is a major immunosuppressive pathogen of poultry, causing aplastic anaemia, lymphoid atrophy, and severe haematopoietic dysfunction in young chicks, thereby posing a substantial threat to global poultry health and production. In this study, a novel highly pathogenic CIAV strain, designated CIAV-GDHY230813, was isolated from young Mahuang chickens in China and subjected to comprehensive molecular and pathogenic characterization. Whole-genome sequencing and phylogenetic analysis revealed that CIAV-GDHY230813 belongs to I-a branch. Notably, the VP1 protein harbored a glutamine residue at position 394, a molecular marker strongly associated with high virulence, together with multiple amino acid substitutions, insertions, and deletions across the coding regions. Pathogenicity experiments in specific-pathogen-free (SPF) chicks demonstrated that infection with CIAV-GDHY230813 resulted in pronounced growth retardation, severe damage to immune organs, and increased mortality. From 3 to 21 days post-infection (dpi), body weights of infected chicks were significantly lower than those of the control group (p < 0.01). Marked thymic and bursal atrophy, splenomegaly, and significantly reduced haematocrit levels were observed, indicating severe anaemia. Furthermore, CIAV infection led to a marked reduction in antibody titres against Newcastle disease virus vaccination by 4-fold to 8-fold, reflecting substantial suppression of humoral immune responses. Quantitative analysis of viral distribution showed significantly elevated viral loads in blood, liver, thymus, spleen, and bursa of Fabricius at both 14 and 21 dpi (p < 0.001), with peak levels detected at 21 dpi. Collectively, these findings demonstrate the strong replicative capacity and high pathogenic potential of CIAV-GDHY230813, providing valuable insights into the molecular epidemiology and pathogenic mechanisms of CIAV in China, supporting improved surveillance and control strategies, and laying a solid foundation for the development of effective vaccines against CIAV.