Sequencing of the Hepatitis C Virus: A Systematic Review

Abstract

Since the identification of hepatitis C virus (HCV), viral sequencing has been important in understanding HCV classification, epidemiology, evolution, transmission clustering, treatment response and natural history. The length and diversity of the HCV genome has resulted in analysis of certain regions of the virus, however there has been little standardisation of protocols. This systematic review was undertaken to map the location and frequency of sequencing on the HCV genome in peer reviewed publications, with the aim to produce a database of sequencing primers and amplicons to inform future research. Medline and Scopus databases were searched for English language publications based on keyword/MeSH terms related to sequence analysis (9 terms) or HCV (3 terms), plus "primer" as a general search term. Exclusion criteria included non-HCV research, review articles, duplicate records, and incomplete description of HCV sequencing methods. The PCR primer locations of accepted publications were noted, and purpose of sequencing was determined. A total of 450 studies were accepted from the 2099 identified, with 629 HCV sequencing amplicons identified and mapped on the HCV genome. The most commonly sequenced region was the HVR-1 region, often utilised for studies of natural history, clustering/transmission, evolution and treatment response. Studies related to genotyping/classification or epidemiology of HCV genotype generally targeted the 5'UTR, Core and NS5B regions, while treatment response/resistance was assessed mainly in the NS3-NS5B region with emphasis on the Interferon sensitivity determining region (ISDR) region of NS5A. While the sequencing of HCV is generally constricted to certain regions of the HCV genome there is little consistency in the positioning of sequencing primers, with the exception of a few highly referenced manuscripts. This study demonstrates the heterogeneity of HCV sequencing, providing a comprehensive database of previously published primer sets to be utilised in future sequencing studies.

Figure 1. Flow diagram describing the review process and study selection.

Figure 2. Positioning of combined and individual sequencing amplicons along the HCV genome.

Sequencing amplicons identified in 434 peer-reviewed studies were categorised into study types, and their location mapped along the length of the HCV genome (A). A measure of genome diversity calculated by Qiu et al illustrates the ranges of low and high genetic variation at regions frequently sequenced (e.g. 5′-untranslated region compared to 5′-region of E2 gene). When viewed individually, the sequencing amplicons show the heterogeneity of sequencing amplicon size and positioning for genotyping/classification (B), treatment response/resistance (C), clustering/transmission (D), natural history (E), evolution (F) and epidemiology (G) study types.