Detection of African horsesickness virus and discrimination between two equine orbivirus serogroups by reverse transcription polymerase chain reaction.

A reverse transcription polymerase chain reaction (RT-PCR), based on the gene encoding the NS2 protein of African horsesickness virus (AHSV), was developed for rapid serogroup-specific detection of AHSV. The specificity of RT-PCR products was confirmed by Southern blot hybridization using a radioactively labelled cDNA probe specific for the NS2 gene. This RT-PCR could discriminate between all known members of the AHSV and equine encephalosis virus serogroups. AHSV RNA was detected in a sample representing 0.005 plaque forming units in a dilution series made of infected cell culture material. In an immune horse which had been vaccinated with a baculovirus expressed AHSV (serotype 4) VP2 subunit vaccine, viral RNA could be detected for up to 22 weeks post challenge. AHSV RNA was detected in various organs of an infected horse. Viral RNA was also detected by RT-PCR in nine suspected field cases of African horsesickness while virus isolation was successfully performed on eight of these cases.