Molecular Characterization of Representative CPV-2c Isolates and Establishment of VP2-Targeted Nanobody-Based...

Although canine parvovirus (CPV) vaccination has been widely implemented, CPV continues to circulate in dog populations and poses a potential cross-species transmission risk to wildlife, including giant pandas. Recent increases in CPV-2c detection in China highlight the need for molecular surveillance and standardized immunoreagents for diagnosis and epitope mapping. This study aimed to isolate a representative CPV-2c strain from China and develop VP2-targeted nanobody-based recognition molecules to support antigen monitoring and detection optimization. Canine and giant panda samples were collected in Sichuan Province, and CPV was isolated in F81 cells, followed by VP2 gene sequencing and phylogenetic analysis. A secretion expression system in Bacillus subtilis was established to produce VP2-targeting nanobodies, and a canine Fc-fused format of Nb10 (Nb10-Fc) was constructed. Immunoreactivity was evaluated via immunoassays, and structural modeling and molecular docking were performed to predict binding interfaces. The results showed that CPV-2c was the dominant genotype in Sichuan, with CPV L4 being a representative strain that exhibited 100% identity in VP2 with a giant panda-derived CPV-2c strain. Nb10 and Nb10-Fc demonstrated strong reactivity in Western blotting and immunofluorescence assays. The Fc-fusion improved detection sensitivity, offering potential in vivo application benefits. This study provides a standardized VP2-specific nanobody and molecular system for CPV-2c surveillance, antigenic studies, and diagnostic optimization.