Identification, prevalence and aspects of molecular biology of hepatitis G virus

Hepatitis G virus (HGV) is a newly identified member of the Flaviviridae family. The positive-sense RNA genome of the virus contains a single open reading frame that encodes the viral polyprotein. Its genomic organization is similar to that of the hepatitis C virus (HCV) with which it has only 25% homology at the nucleotide level. Nucleotide sequences from the NS-3 helicase region of HCV varied by 10-30%. HGV is therefore much less variable than HCV. Construction of phylogenetic trees, and calculation of mean distances between possible subtypes, indicated one level of variation in NS-3 sequences: the degree of variation between isolates was similar to that observed between HCV subtypes. Thus no evidence for clustering of sequences into multiple genotypes was found. The virus is transmissible through blood transfusion and by exposure to blood products or intravenous drug use, and may result in acute or chronic hepatitis. A causative role of HGV in acute and chronic hepatitis is not yet established. Concurrent infection with hepatitis B virus (HBV) and HCV is common and persistent viraemia has been documented for many years, in many cases, in the absence of transaminase elevations.