Genus: Ichtadenovirus

Genus: Ichtadenovirus

Distinguishing features

The single known member of this genus, white sturgeon adenovirus 1 (WSAdV-1), is the only confirmed fish adenovirus (Benkő et al., 2002). It was isolated and propagated on a white sturgeon cell line. This host is very divergent from those of other adenoviruses, and phylogenetic calculations and a unique genome organization further distinguish this virus from all other adenoviruses (Kovács et al., 2003, Doszpoly et al., 2019). The WSAdV-1 genome is longer than that of any known adenovirus. The fiber gene was not found in its usual position towards the right end of the genome, but fiber gene homologues have been discovered at the left end (Doszpoly et al., 2019) (Figure 2.Adenoviridae).

Virion

Morphology

Although electron micrographs have been produced of WSAdV-1, the morphology (including the locations of the presumed four different fiber proteins) is not known. Bacterial expression of the putative fiber genes has failed thus far.

Physicochemical and physical properties

Not known.

Nucleic acid

The WSAdV-1 genome is 48,395 bp, and therefore is the longest of any known adenovirus (Doszpoly et al., 2019). The nucleotide composition is 42.63% G+C. The inverted terminal repeats (ITRs) are 126 bp.

Proteins

Four fiber-like proteins are proposed to be expressed by this virus based on the level of similarity to fiber proteins of other adenoviruses, but their functions have not yet been studied. This number of potential fiber genes is thus so far unique among adenoviruses, and it is probable that only two of them function to generate fiber proteins. WSAdV-1 has orthologues of the 16 family-common genes, and these proteins are presumed to have roles similar to those in other adenoviruses. However, the virus has a further 28 ORFs that presumably code for at least this number of additional proteins. Most have no similarity to any known adenovirus proteins; the two exceptions distantly resemble the parvovirus NS proteins, homologues of which occur in certain avian adenoviruses.

Lipids

None reported.

Carbohydrates

See discussion under family properties.

Genome organization and replication

The left genome end contains four fiber-like genes, three of which are located tandemly and transcribed rightward, followed by a fourth transcribed leftward. To the right of these genes is located the conserved region encoding 16 family-common genes. Further to the right is a region extending to the right terminus that accounts for >42% of the entire genome. A total of 28 ORFs potentially encoding proteins of >50 amino acid residues are present in this region (Figure 2.Adenoviridae). Only two WSAdV-1 genes are predicted to be spliced: those encoding pTP and 33K (which are also spliced in all other adenoviruses).

Biology

The virus seems to be non-pathogenic for fish.

Antigenicity

See discussion under family properties.

Species demarcation criteria

There is currently a single species in the genus; demarcation criteria have not been defined.

Member species

Exemplar isolate of the species
SpeciesVirus nameIsolateAccession numberRefSeq numberAvailable sequenceVirus Abbrev.
Sturgeon ichtadenovirus Awhite sturgeon adenovirus 1WSAdV1/1996MK101347Complete genomeWSAdV-1

Virus names, the choice of exemplar isolates and virus abbreviations are not official ICTV designations.