Monitoring of African horse sickness Virus-Specific Antibodies in horses, northeastern Thailand

Abstract

African horse sickness (AHS) is caused by infection with the African horse sickness virus (AHSV). In March 2020, AHS was first reported in Thailand due to the importation of subclinically infected host animals, such as zebras. In this study, we conducted a serological survey for AHSV-specific antibodies across 21 horse farms in the northeastern provinces (n=3) of Thailand. A total of 600 serum samples were collected for cross-sectional (n = 292) and longitudinal serological monitoring (n = 308). A cross-sectional study was conducted in 2020, during which serum samples (n = 292) were collected and tested for AHS antibodies using the ELISA test. Our results showed that horses from non-vaccinated farms tested negative for the ELISA test, while horses from the vaccinated farm had positive AHS antibodies. From April to November 2020, following the first vaccination with a polyvalent vaccine (serotypes 1, 3, and 4), longitudinal serum samples (n = 91) were collected at 30, 90, and 180 days post-vaccination (dpv). From May to December 2021, after the second vaccination with the AHSV monovalent vaccine (serotype 1), serum samples (n=217) were collected at 0, 14, 30, 90, and 180 days post-vaccination. The results from the longitudinal study demonstrated that the live-attenuated AHS polyvalent vaccine (serotypes 1, 3, and 4) can induce a high AHS-antibody response lasting up to 6 months post-vaccination. The annual booster with monovalent vaccination (serotype 1) also produced a strong antibody response, which persisted up to 6 months post-vaccination. In summary, the information on serological monitoring of AHSV-specific antibodies in Thailand is useful for strategic planning to prevent and control the disease in the future.