A new duplex real-time RT-PCR assay for sensitive and specific detection of African horse sickness virus

A novel duplex real time quantitative reverse transcription polymerase chain reaction for rubella virus with armored RNA as a noncompetitive internal positive control

The objective of this study was to build and apply a duplex real time quantitative reverse transcription-polymerase chain reaction (RT-PCR) for rubella virus. Firstly, a 60-bp-long armored RV RNA was constructed in the laboratory. Secondly, a duplex real time RT-PCR assay was established. Thirdly, the 60-bp-long armored RV RNA was used as an internal positive control (IPC) for the duplex real time RT-PCR. And finally the duplex real time RT-PCR assay was applied to detect RV RNA in clinical specimens. The in-house assay has a high amplification efficiency (0.99), a high analytical sensitivity (200 copies/mL), and a good reproducibility. The diagnostic specificity and sensitivity of the in-house assay were both 100%, due to the monitoring of the armored RV RNA IPC. Therefore, the in-house duplex real time quantitative RT-PCR assay is a specific, sensitive, reproducible and accurate assay for quantitation of RV RNA in clinical specimens. And noncompetitive armored RV RNA IPC can monitor RT-PCR inhibition and prevent false-negative and inaccurate results in the real time detection system.

Real time RT-PCR assays for detection and typing of African horse sickness virus

Although African horse sickness (AHS) can cause up to 95% mortality in horses, naïve animals can be protected by vaccination against the homologous AHSV serotype. Genome segment 2 (Seg-2) encodes outer capsid protein VP2, the most variable of the AHSV proteins. VP2 is also a primary target for AHSV specific neutralising antibodies, and consequently determines the identity of the nine AHSV serotypes. In contrast VP1 (the viral polymerase) and VP3 (the sub-core shell protein), encoded by Seg-1 and Seg-3 respectively, are highly conserved, representing virus species/orbivirus-serogroup-specific antigens. We report development and evaluation of real-time RT-PCR assays targeting AHSV Seg-1 or Seg-3, that can detect any AHSV type (virus species/serogroup-specific assays), as well as type-specific assays targeting Seg-2 of the nine AHSV serotypes. These assays were evaluated using isolates of different AHSV serotypes and other closely related orbiviruses, from the ‘Orbivirus Reference Collection’ (ORC) at The Pirbright Institute. The assays were shown to be AHSV virus-species-specific, or type-specific (as designed) and can be used for rapid, sensitive and reliable detection and identification (typing) of AHSV RNA in infected blood, tissue samples, homogenised Culicoides, or tissue culture supernatant. None of the assays amplified cDNAs from closely related heterologous orbiviruses, or from uninfected host animals or cell cultures.

Development of a real time polymerase chain reaction assay for equine encephalosis virus

Equine encephalosis virus (EEV) is the cause of equine encephalosis. The disease is similar to mild forms of African horse sickness (AHS) and the two diseases are easily confused. Laboratory identification and serotyping of EEV is based on viral isolation in BHK-21 cells and a viral plaque inhibition neutralisation test. These procedures are time-consuming and therefore a more rapid diagnostic assay for EEV that can distinguish EEV from African horse sickness virus (AHSV) infections was developed. The S7 (VP7) gene from 38 EEV isolates representing all seven serotypes was amplified and sequenced. A conserved region at the 5' end of the gene was identified and used to design group-specific EEV primers and a TaqMan(®) MGB™ hydrolysis probe. The efficiency of the EEV real-time RT-PCR assay was 81%. The assay was specific, as it did not detect any of the nine serotypes of AHSV, nor 24 serotypes of bluetongue virus (BTV) and sensitive, with a 95% limit of detection of 10(2.9) TCID50/ml blood (95% confidence interval: 10(2.7) to 10(3.3)). The real-time format was selected because of its convenience, sensitivity and ability to produce results rapidly.