Detection of African horse sickness virus in the blood of experimentally infected horses: comparison of virus isolation and a PCR assay.

A reverse transcription-polymerase chain reaction (RT-PCR) assay followed by dot-blot hybridisation was used to detect African horse sickness virus (AHSV); the primers employed amplified the S7 gene that encodes the VP7 protein. The RT-PCR assay was compared with virus isolation for detecting AHSV in blood samples form horses experimentally infected with AHSV-4 and AHSV-9. The influence of sample storage and transportation and the effects of two anticoagulants (EDTA and heparin) were also studied. RT-PCR results were obtained within 48 hours as opposed to a minimum of 15 days for virus isolation. RT-PCR and virus isolation were equally sensitive for detection of AHSV-4. Viraemia was detected more consistently by RT-PCR than by virus isolation from horses infected with the less virulent AHSV-9 isolate except from one animal in which virus was detected only by virus isolation. The sensitivity of virus isolation was increased by passaging samples five times. This study indicates that RT-PCR is a sensitive and rapid method for use in the face of an outbreak of this serious disease, although it has also some limitations as a diagnostic technique.