Isolation and Genetic Characterization of Three Palyam Serogroup Orbiviruses From Culicoides Spp. and Associated Infections in Cattle in Yunnan, China

Palyam serogroup virus (PALV) is a potential pathogen prevalent in Asia, Australia, and Africa that may cause abortion and teratogenesis in ruminants, especially cattle. In this study, we isolated three PALV strains (MY_C17, ML_C40, and SZ_C06) from Culicoides spp. in Yunnan, China, and obtained their complete genome sequences via next-generation sequencing. The phylogenetic analysis of Seg-5, Seg-7, and Seg-9 indicated that PALVs can be grouped based on their geographical origins: Asia, Australia, and Africa. The three isolates in this study belong to the Asia group. However, the Central African Republic strain (AR_B_2032) and the India strain (DVTD) form a separate branch, provisionally named the CI group. In the VP2 phylogenetic tree, all PALV strains can be grouped into six significant branches, designated as A through F. The three isolates are clustered in Groups A, E, and F and are shown to belong to the D’Aguilar virus (DAGV), Chuzan virus (CHUV), and Bunyip Creek virus (BCV) serotypes, respectively. Seroepidemiological surveys were conducted on local cattle using neutralization tests, which revealed seroprevalence rates of neutralizing antibodies against BVC, DAGV, and CHUV in Yunnan cattle serum of 3.4% (12/350), 6.9% (24/350), and 16.9% (59/350), respectively. This marks the first-ever isolation of CHUV, specifically BCV and DAGV, from vector Culicoides spp. in Southwest China. It was also proved that in this region, at least three serotypes of PALV circulated among Culicoides spp. in nature and infected domestic cattle.