Passive transfer and rate of decay of maternal antibody against African horse sickness virus in South African Thoroughbred foals.

This research focuses on determining the antibody levels against the African horse sickness virus (AHSV) of broodmares vaccinated with a live-attenuated AHSV vaccine, as well as the efficiency and decay rate of these vaccines in their foals. It was found that there is a difference in the response to vaccination among mares and in the derived immunity in foals based on the specific AHSV serotypes.

African Horse Sickness and Vaccination

• African horse sickness (AHS) is a lethal disease among horses transmitted by insects. It is caused by the African horse sickness virus (AHSV) which has 9 different serotypes.
• An attenuated AHSV vaccine is commonly used in southern Africa where AHS is endemic. This vaccine is bred in a lab to be low-risk but still trigger an immune response.
• A lack of studies on vaccinated horses’ antibody responses has prompted this research, aimed at understanding the effectiveness of the current AHSV vaccination program.

Objective and Methodology

• The research aimed at determining the levels of antibodies reacting to the 9 known AHSV serotypes in a group of broodmares that were regularly vaccinated with the AHSV vaccine.
• The study further sought to understand how well these antibody levels are preserved in the foals of these vaccinated mares, and how quickly they decay over time.
• Serum, the liquid portion of blood, was collected from 15 mares before they foaled and from their offspring monthly for six months. The serum was tested for its ability to neutralize different serotypes of AHSV.

Findings

• The results indicated that the mares’ antibody responses varied by serotype, meaning some serotypes provoked higher levels of protection than others despite repeated vaccinations.
• This variation expanded to their offspring; the duration of maternal antibodies also depended on the serotype.

Conclusions and Implications

• The inconsistency in the response to different AHSV serotypes in both mares and foals suggests that the strains included in the vaccine may not all be equally effective at provoking an immune response.
• Furthermore, the wide range of maternal antibody levels in foals signifies differences in passive immunity by serotype.
• This research is essential in understanding how to use vaccines most effectively both in AHSV-endemic regions and in regions at risk of the disease. The variation in response to different serotypes will indicate when optimal timing for foal vaccination might be.
• However, further research involving more horses is necessary to establish more concrete vaccination guidelines.