Identification and Genetic Characterization of a Strain of African Horse Sickness Virus Serotype 1 and Its Safety Evaluation in a Mouse Model

African horse sickness (AHS) is an arthropod-borne, severe equid disease caused by African horse sickness virus (AHSV). AHSV has high mortality and is endemic to sub-Saharan Africa. It has been classified into nine distinct serotypes (AHSV-1 to AHSV-9) based on VP2 immunogenicity. The AHS outbreak in Thailand in 2020, caused by AHSV-1, marked the first occurrence of this disease in Southeast Asia. It posed a substantial threat to the security of the equine industry in the nations across the region. To ensure the emergency reserve for AHS prevention and control, the AHSV strain imported to China from abroad over 60 years ago was characterized in this study. The strain was passaged in mice and then blind-passaged in Vero cells. The plaque purification method was then used to purify the strain and obtain its cell-adapted version, named AHSV/C. Neutralization tests confirmed that the virus belongs to AHSV-1. Whole-genome sequencing revealed that AHSV/C was highly homologous to AHSV-1 isolate 1180, with over 95% homology of major antigenic protein VP2, as compared to other AHSV-1 strains, including the prevalent strain in Thailand. In the mouse models, AHSV/C exhibited no clinical signs or histopathological lesions, suggesting low virulence and safety. This research for the first time characterized the in vitro growth characteristics and viral subtypes of the AHSV in China, determined its complete whole-genome sequence, and evaluated its safety using a mouse model. It provides crucial experimental materials and scientific foundations for the development of diagnostic methods and vaccines against AHSV-1.