New Hepatitis B-like virus family discovered: Nackednaviruses

The family Hepadnaviridae contains Hepatitis B viruses that are enveloped viruses with reverse-transcribed DNA genomes.

However, recently scientists reported the discovery of a diversified family of fish viruses, designated Nackednaviruses, which lack the envelope protein gene, but otherwise exhibit key characteristics of Hepatitis B viruses, including genome replication via protein-primed reverse-transcription and utilization of structurally related capsids[1].

Phylogenetic reconstruction indicates that these two virus families, Hepadnaviridae and Nackednaviruses, separated more than 400 million years ago, even before the rise of tetrapods. Therefore, Hepatitis B viruses are of ancient origin, descending from non-enveloped progenitors in fishes.

Their envelope protein gene emerged de novo, leading to a major transition in viral lifestyle, followed by co-evolution with their hosts over geologic eras.

The scientists identified Hepatitis B-related viruses by homology searching in public sequence databases at the National Center for Biotechnology Information (NCBI). What they found were three new Hepatitis B-like viruses: African Cichlid Nackednavirus (ACNDV), Rockfish Nackednavirus (RNDV) and Sockeye Salmon Nackednavirus (SSNDV).

[1] Lauber et al: Deciphering the Origin and Evolution of Hepatitis B Viruses by Means of a Family of Non-enveloped Fish Viruses in Cell Host & Microbe – 2017. See here.