Serological response of foals to polyvalent and monovalent live-attenuated African horse sickness virus vaccines

Abstract

African horse sickness (AHS) is typically a highly fatal disease in susceptible horses and vaccinationis currently used to prevent the occurrence of disease in endemic areas. Similarly, vaccination has beencentral to the control of incursions of African horse sickness virus (AHSV) into previously unaffected areasand will likely play a significant role in any future incursions. Horses in the AHSV-infected area in SouthAfrica are vaccinated annually with a live-attenuated (modified-live virus [MLV]) vaccine, which includesa cocktail of serotypes 1, 3, 4 (bottle 1) and 2, 6–8 (bottle 2) delivered in two separate doses at least 21days apart. In this study, the neutralising antibody response of foals immunized with this polyvalentMLV AHSV vaccine was evaluated and compared to the response elicited to monovalent MLV AHSVserotypes. Naïve foals were immunized with either the polyvalent MLV AHSV vaccine, or a combinationof monovalent MLV vaccines containing individual AHSV serotypes 1, 4, 7 or 8. There was a markedand consistent difference in the immunogenicity of individual virus serotypes contained in the MLVvaccines. Specifically, foals most consistently seroconverted to AHSV-1 and responses to other serotypeswere highly variable, and often weak or not detected. The serotype-specific responses of foals given themonovalent MLV vaccines were similar to those of foals given the polyvalent MLV preparation suggestingthat there is no obvious enhanced immune response through the administration of a monovalent vaccineas opposed to the polyvalent vaccine.