A real-time quantitative reverse transcription-PCR (qRT-PCR) assay using the recombinant thermostable Thermus thermophilus (rTth) enzyme was developed to detect and quantify rotavirus A (RVA). By using rTth polymerase, significant improvement was achieved over the existing real-time RT-PCR assays, which require denaturation of the RVA double-stranded RNA (dsRNA) prior to assay setup. Using a dsRNA transcript for segment 7, which encodes the assay target NSP3 gene, the limit of detection for the improved assay was calculated to be approximately 1 genome copy per reaction. The NSP3 qRT-PCR assay was validated using a panel of 1,906 stool samples, 23 reference RVA strains, and 14 nontarget enteric virus samples. The assay detected a diverse number of RVA genotypes and did not detect other enteric viruses, demonstrating analytical sensitivity and specificity for RVA in testing stool samples. A XenoRNA internal process control was introduced and detected in a multiplexed qRT-PCR format. Because it does not require an antecedent dsRNA denaturation step, this assay reduces the possibility of sample cross-contamination and requires less hands-on time than other published qRT-PCR protocols for RVA detection.
Group A rotaviruses (RVA) are estimated to cause 453,000 deaths among infants and young children each year (1). The genome of RVA, members of the Reoviridae family, consists of 11 double-stranded RNA (dsRNA) segments which encode six viral structural proteins (VP1 to VP4, VP6, and VP7) and six nonstructural proteins (NSP1 to NSP6) (2). Surrounding the dsRNA are three concentric protein layers, namely, a central core (VP2), a middle protein layer (VP6), and an outer capsid composed of VP7 and VP4 proteins, while the viral RNA-dependent RNA polymerase (VP1) and the RNA capping enzyme (VP3) are packaged within the core shell (3). Traditionally, viral classification has been based on the serological characteristics and sequence diversity of the outer capsid proteins, VP7 (glycosylated, G-type) and VP4 (protease sensitive, P-type) (4). Although 27 G genotypes and 35 P genotypes have been identified to date (5) Numerous techniques have been developed to detect RVA in stool samples. These techniques include, but are not limited to, virus isolation in cell culture, electron microscopy (EM), enzyme immunoassays (EIA), coupled reverse transcription and PCR amplification (RT-PCR), and real-time quantitative RT-PCRs (qRTPCRs) (2, 7-19). The molecular techniques are more rapid than the cell culture-based techniques and are more sensitive than EM or EIA. The threshold for detection of RVA by EM is approximately 10 7 viral particles/ml of stool (20). EIAs are 10 to 100 times more sensitive than EM assays, but the sensitivity and specificity of EIAs are more variable (21-23). A number of studies using RT-PCR assays targeting the RVA VP4, VP6, and VP7 gene segments have shown increases of 15% to 27% in the rate of RVA detection in comparison with . RT-PCR assays employ either one-step or two-step reverse transcription followed by an ...