Family: Hepadnaviridae

Genus: Metahepadnavirus

Distinguishing features

Metagenomic sequence analysis of lip tissues from bluegill (Lepomis macrochirus, Perciformes, Actinopterygii) with orocutaneous neoplasms in two fish populations from an aquarium in Georgia USA revealed hepadnavirus-like sequences, which were further confirmed by PCR amplification and sequencing with specific primers. This virus is designated as bluegill hepatitis B virus, (BGHBV). 

The genomes of metahepadnaviruses have the characteristic of hepadnaviral ORFs, but lack the X-gene of orthohepandaviruses and the pre-C region of avi- and orthohepadnaviruses. 

The virus genome has an expanded reverse transcriptase domain with more than 40 amino acids overlapping the immunodominant “a”-determinant encoded by the S-gene. This feature is shared with the orthohepadnaviruses. The virus was identified in a broad spectrum of tissues and organs in contrast to avi- and orthohepadnaviruses, where the virus is thought to mainly replicate in the liver. 

Virion

See discussion under family description. 

Genome organization and replication

See discussion under family description. 

Biology

Viruses of fresh and salt water teleosts. The viruses are able to switch host fish. 

Species demarcation criteria

BGHBV is classified in the species Bluegill hepatitis B virus, which is the only species of the genus. BGHBV was identified by metagenomic sequencing of lip samples from bluegill (Dill et al., 2016). The virus was also identified in liver and skin samples from bluegill by PCR. 

Related, unclassified viruses 

Apart from BGHBV, there are additional virus isolates that may represent three tentative species in the genus. These viruses were identified from teleost fish samples by metagenomic sequencing. These three viruses are: icefish metahepadnavirus (IMDV) from the muscle of crocodile icefish (Chionodraco hamatus), Astatotilapia metahepadnavirus (AMDV) from Astatotilapia (Astatotilapia sp.) and tetra metahepadnavirus (TMDV) from the eye-surface of Mexican tetra (Astyanax mexicanus) (Lauber et al., 2017). 

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.