Family: Hepadnaviridae

Genus: Herpetohepadnavirus

Distinguishing features

BLAST analyses of WGS databases in GenBank identified a complete hepadnavirus genome from a muscle sample from the Tibetan frog (Nanorana parkeri, Anura, Amphibia). The virus Tibetan frog hepatitis B virus (TFHBV) is classified in the species Tibetan frog hepatitis B virus (Dill et al., 2016). 

This virus genome lacks the X-gene found in orthohepadnaviruses.  

Virion

See discussion under family description. 

Genome organization and replication

See discussion under family description. 

Biology

Viruses infect poikilothermic tetrapods, amphibia and reptiles. As is the case for avihepadnavirus, integration of viral sequences into host genomes are reported. 

Species demarcation criteria

The virus Tibetan frog hepatitis B virus (TFHBV) is classified in the species Tibetan frog hepatitis B virus, which is the only species of the genus. 

Related, unclassified viruses

Metagenomic sequencing has identified two exogenous hepadnaviruses genetically similar to herpetohepadnavirus (Lauber et al., 2017). One was isolated from a skink (Saproscinus basilikus) and designated skink hepatitis B virus (SkHBV), and another from liver from a spiny lizard (Sceloporus adleri) and designated spiny lizard hepatitis B virus (SLHBV-1). 

Virus names and virus abbreviations are not official ICTV designations. 

#GenBank accession number not available, but the sequence can be obtained from the alignment file associated with Figure 4. Hepadnaviridae and provided in the Resources section of this Report. 

Endogenous unclassified viruses

Endogenous hepadnavirus genomes have been identified in snakes, and designated eSnHBV-1 (Gilbert and Feschotte 2010). The integrated hepadnavirus genomes in rattlesnake (Crotalus mitchellii) vary in length from 316 to 370 codons with 48-67% amino acid similarity to the corresponding region of the avihepadnavirus polymerase (Gilbert and Feschotte 2010). An additional four endogenous hepadnavirus genomes have been identified, in common garter snake (Thamnophis sirtalis), in corn snake (Pantherophis guttatus), in pit viper (Protobothrops mucrosquamatus), and in common European viper (Vipera berus). The integrated genomes were flanked by different host sequences, indicating independent integration events in the different hosts. However, since the genomes have, so far, only been identified in host genomes, it may indicate that they are not viral genomic sequences with replication capacity, and therefore should not be classified as members of the Hepadnaviridae.