| Virus Group IV|
| Betanodavirus, Tetraviridae, Tombusviridae, Leviviridae, Birnaviridae|
Nodaviridae is a family of viruses. Vertebrates and invertebrates serve as natural hosts. There are currently nine species in this family, divided among 2 genera. Diseases associated with this family include: viral encephalopathy and retinopathy in fishes.
The virus is not enveloped and has an icosahedral capsid (triangulation number=3) ranging from 29 to 35 nm in diameter. The capsid is constructed of 32 capsomers.
The genome is linear, positive sense, bipartite (composed of two segments—RNA1 and RNA2) single stranded RNA consisting of 4500 nucleotides with a 5’ terminal methylated cap and a non-polyadenylated 3’ terminal.
RNA1, which is ~3.1 kilobases in length, translates encodes a protein that has multiple functional domains: a mitochondrial targeting domain, a transmembrane domain, an RNA-dependent RNA polymerase (RdRp) domain, a self-interaction domain and an RNA capping domain. In addition, RNA1 encodes a subgenomic RNA3 that translates protein B2, an RNA silencing inhibitor.
RNA2 encodes protein α, a viral capsid protein precursor, which is auto-cleaved into two mature proteins, a 38 kDa β protein and a 5 kDa γ protein, at a conserved Asn/Ala site during virus assembly.
Viral replication is cytoplasmic. Entry into the host cell is achieved by penetration into the host cell. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription, using the internal initiation model of subgenomic RNA transcription is the method of transcription. Vertebrates and invertebrates serve as the natural host. Transmission routes are contact and contamination.
The members of the alphanodoviridae were originally isolated from insects while those of the betanodoviridae were isolated from fish. A small number of nodoviruses seem to lie outside either of these clades.
While NoV remains the type species for this group, Flock house virus (FHV) is the best studied of the Nodaviruses.