Genomic, antigenic, and seroepidemiological characterization of an antigenically divergent Tibet orbivirus strain isolated from Culicoides in China.

Tibet orbivirus (TIBOV) is a poorly characterized orbivirus whose antigenic diversity and circulation in livestock remain incompletely defined. Here, we report the isolation of a TIBOV strain, MS18C217-16, from Culicoides spp. collected in Mangshi, Yunnan Province, China, in 2018. MS18C217-16 replicated efficiently in multiple mammalian cell lines and induced clear cytopathic effects. Phylogenetic analysis assigned the isolate to the TIBOV clade, with high amino acid conservation in VP1, VP3, and VP7, but marked divergence in the outer-capsid proteins VP2 and VP5. Structural modeling and predicted MHC class II-binding peptide profiles suggested distinctive antigenic features in these proteins, and neutralization assays provided evidence that MS18C217-16 is antigenically distinct from the reference TIBOV strain DH13C120. Serological surveys detected neutralizing antibodies in goats, swine, and cattle across four counties, with particularly high seropositivity in goats from Mengla. Together, these data identify MS18C217-16 as an antigenically divergent TIBOV strain with features consistent with a putative novel serotype, while highlighting the need for reciprocal cross-neutralization assays using strain-specific antisera for formal serotype confirmation.