Quantitation of hepatitis delta virus using a single-step internally controlled real-time RT-qPCR and a full-length genomic RNA calibration standard.

Quantitation of circulating hepatitis delta virus (HDV) RNA is important for assessing the response to antiviral therapy and for understanding the complex dynamic interactions between hepatitis B virus (HBV) and HDV replication. Although several PCR assays for HDV RNA have been described none of them incorporate an internal control or use a full-length RNA calibration standard for absolute quantitation. This study describes the development and evaluation of a novel single-step real-time RT-qPCR assay for HDV RNA quantitation which incorporates a Brome Mosaic virus internal control to prevent false negatives and under-reporting due to inhibitors or due to inefficient RNA purification, reverse transcription or PCR amplification. The assay has a dynamic range of ≥7log(10) and is designed to detect all HDV genotypes. The 95% detection limit is ∼3800 HDV RNA copies/ml, 700 copies/ml being detectable in 20% of repeats. Both intra-assay and inter-assay variability are low (CV 8% and 17%, respectively). Plasma HDV RNA was detected in 75% of 59 HDV antibody-positive samples with titres ranging from 8.4×10(4) to 4.4×10(8) copies/ml. The assay described provides a reliable and sensitive quantitative system for therapeutic monitoring and for studying the dynamic interplay between hepatitis B virus replication and HDV viral load.