Preliminary Assessment on Pathogenicity of an African Horse Sickness Virus Serotype 1 Strain in Guinea Pigs and Horses

African horse sickness (AHS), a noncontagious insect-borne disease affecting equids, is caused by the African horse sickness virus (AHSV) and is associated with extremely high morbidity and mortality. AHSV has nine distinct serotypes (AHSV-1 to AHSV-9). In a previous study, we characterized the genome and in vitro growth properties of AHSV/C, a cell-adapted derivative of an AHSV-1 strain imported into China 60 years ago, and verified its safety in mice. This study preliminarily explored the pathogenicity of AHSV/C in guinea pigs and horses (its natural host). Six groups of guinea pigs were inoculated with three doses of AHSV/C (107.5, 106.5, and 105.5 TCID50 per animal) via both intraperitoneal and subcutaneous routes; two horses were subcutaneously inoculated with 105.5 TCID50 of AHSV/C. All animals received a booster inoculation three weeks later. During the entire observation period, we mainly monitored clinical signs, body temperature, viremia, virus shedding and pathological changes (examined only in guinea pigs), and collected serum samples for neutralizing antibody detection. The results showed that no abnormal clinical signs, evident viremia, or virus shedding were observed in either species. Histopathological examinations revealed no evident lesions in guinea pigs. Neutralization tests showed that AHSV/C induced only low neutralizing antibody titers after primary inoculation, with a marked increase after booster administration. Collectively, this study preliminarily characterized the pathogenicity of AHSV/C in guinea pigs and horses, confirming that the strain showed no evident pathogenicity in test animals. These findings suggest that AHSV/C may be an attenuated strain. Further studies with larger sample sizes are required to validate these findings and explore their potential applications.