Humoral antibody response of 10 horses after vaccination against African horse sickness with an inactivated vaccine containing all 9 serotypes in one injection

Abstract

Background: African horse sickness (AHS) is a devastating viral disease of equids that was first recorded in 1327. Currently, prevention and control of the disease are based on attenuated vaccines and midge control. It has been shown that attenuated Orbivirus vaccines are not always safe as they may reverse to virulence.

Objectives: In the Emirate of Dubai, a vaccination experiment was carried out with an inactivated AHS vaccine produced at the Central Veterinary Research Laboratory (CVRL), Dubai, UAE to investigate the humoral antibody response of AHS-naïve horses to this vaccine. Our vaccination experiment was performed to establish an AHS vaccine bank in the UAE to protect horses from the disease in case of an outbreak. Therefore, CVRL established an inactivated AHS vaccine containing all nine serotypes which induce high neutralising antibodies.

Study design: A total of 10 horses kept in a desert isolation area were subcutaneously and intramuscularly vaccinated with an inactivated vaccine containing all nine AHS serotypes previously isolated from Kenyan horse fatalities. Primary immunisation was followed by two booster immunisations 4 weeks and 6 months apart. After 13 months, an annual booster was administered.

Methods: Blood samples were regularly withdrawn for ELISA and virus neutralisation testing. Additionally, EDTA blood was tested every second day for 14 days post each vaccination for the presence of AHS virus or its RNA.

Results: Results show that ELISA and virus neutralising antibodies appeared after the first booster, declined after 4-6 months and therefore three vaccinations and an annual vaccination are necessary to achieve high protective virus neutralising antibodies.

Main limitations: No challenge infection was carried out due to the lack of a safe facility in the UAE.

Conclusion: Before more advanced AHS vaccines become a reality, inactivated vaccines containing all nine serotypes should be used as they produce high ELISA and neutralising antibodies.

Keywords: African horse sickness; horse; immune response; inactivated vaccine with 9 serotypes.