Genomic Epidemiology and National Seroprevalence Reveal the Widespread Distribution of Palyam Viruses in China.

The taxonomic species Palyam virus (PALV) comprises a group of widely distributed, Culicoides-borne arboviruses linked to bovine reproductive disorders, yet its genetic diversity and seroprevalence in China have not been fully characterized. To address this gap, we obtained 29 PALV isolates from sentinel cattle in southern China, performed whole-genome sequencing on 15 representative strains, and conducted a nationwide serosurvey of 4660 cattle using a newly developed c-ELISA. These genomic data were integrated with global datasets for comprehensive phylogenetic and phylogeographic analyses. By establishing a global VP2-based framework, the Chinese PALV isolates were assigned to the Chuzan, Bunyip Creek, and D'Aguilar genogroups. In the global context, Chinese PALV strains exhibited the closest genetic affinity with strains from Japan, while phylogeographic reconstruction suggests at least two independent introductions from Japan during the 1980s and 1990s. Our survey revealed a high overall seroprevalence of 46.5% (95% CI: 44.7-47.5%) in cattle, demonstrating a pronounced latitudinal gradient with a sharp ecological threshold at 32.5° N. The virus is hyperendemic in humid southern China, with seroprevalence ranging from 33.0% to 88.8%, but attenuated in northern regions with seroprevalence less than 8.0%. These findings redefine PALV as a widespread "silent threat" in the East Asian arbovirus ecosystem, highlighting the need for coordinated transboundary surveillance.