Hepatitis delta virus genetic variability: from genotypes I, II, III to eight major clades?

Hepatitis D virus (HDV) is a satellite of hepatitis B virus (HBV) for transmission and propagation, and infects nearly 20 million people worldwide. The HDV genome is composed of a compact circular single-stranded negative RNA genome with extensive intramolecular complementarity. Along with epidemiological, geographic distribution and pathological patterns, the variability of HDV has been limited to three genotypes and two subtypes that have been characterized to date. Recently, extensive phylogenetic reconstructions based on the delta antigen gene and full-length genome sequence data, have shown a wide and probably ancient radiation of African lineages, suggesting that the genetic variability of HDV is much more complex than previously thought. Indeed, sequences previously affiliated with genotype IIb should now be considered as belonging to clade 4 (HDV-4) and African HDV sequences segregate within four additional clades: HDV-5, HDV-6, HDV-7 and HDV-8. These results bring the geographic distribution of HDV closer to the genetic variability of its helper HBV.