Using a new serotype-specific Polymerase Chain Reaction (PCR) and sequencing to differentiate between field and vaccine-derived African Horse Sickness viruses submitted in 2016/2017.

The research article discusses the development and use of a new serotype-specific Polymerase Chain Reaction (PCR) for differentiating between field and vaccine-derived African Horse Sickness (AHS) viruses that were submitted in 2016/2017, importantly aiding in the monitoring and control of horse sickness and guiding policy regarding equine vaccination and trade.

Study’s Objective

• This study aimed to develop a new serotype-specific Polymerase Chain Reaction (PCR) test that can differentiate between field and vaccine-derived African Horse Sickness (AHS) viruses.

Methodology

• The researchers targeted the segment 2 (Seg-2) of the AHS virus that encodes the outer capsid viral protein 2 (VP2), as this segment is the most variable and determines the virus serotype.
• They compared full-length segment 2 sequences from more than 100 AHS viruses isolated over the last 80 years, identifying single nucleotide polymorphisms (SNPs) between the reference strains and recent field viruses.
• The team identified regions unique to each individual serotype and designed primers to differentially amplify each of the nine serotypes.
• The sequences of resulting amplicons contained a significant amount of SNPs that could be used to discriminate between field viruses and reference strains or live attenuated viruses.
• This serotype-specific RT-PCR method was used to determine the prevalence of different AHSV serotypes amongst samples submitted to the Agricultural Research Council – Onderstepoort Veterinary Research Institute (ARC-OVR) during the 2016/2017 season.
• Sequencing of the PCR products was carried out to ascertain if the infections were caused by field or vaccine-derived strains.

Findings

• The serotypes of 70 AHSV positive diagnostic samples submitted to ARC-OVR were determined, with Serotypes 2 and 6 found to be the most prevalent.
• Serotype 1 was the only serotype where sequences identical to the ALV or reference strains were detected in field samples, indicating that they may have been derived from vaccinations than natural infections.

Implications

• The research found that the incidence of vaccine-derived AHS infections submitted from southern Africa was low.
• The serotype-specific RT-PCR and sequencing assay developed in this research could be used in monitoring and controlling the movement of horses both nationally and internationally. It can also provide crucial scientific guidance concerning the policies and guidelines regulating vaccination and trade of equines in South Africa.