Novirhabdoviruses

Novirhabdoviruses are a genus of the family Rhabdoviridae within the order Mononegavirales. They are enveloped, bullet-shaped viruses with negative-sense single-stranded RNA genomes. The genus comprises several fish-infecting viruses, including Infectious hematopoietic necrosis virus (IHNV), Viral hemorrhagic septicemia virus (VHSV), and Hirame rhabdovirus (HIRRV).

Like other rhabdoviruses, novirhabdoviruses have a single, negative-sense RNA genome that encodes multiple structural proteins and a nonstructural nv gene. The genome is roughly 11 to 12 kilobases in length and includes the canonical N, P, M, G and L genes, plus an additional NV gene unique to this group. The NV protein is produced during infection but is not part of the virion; it is believed to influence virulence and interactions with the host immune system. Virions are enveloped and typically bullet-shaped, measuring about 100 to 150 nanometers.

Host range and disease manifestations are centered on fish. IHNV causes infectious hematopoietic necrosis, particularly in juvenile salmonids, with tissue necrosis and high mortality. VHSV has a broader host range, infecting numerous freshwater and marine fish and causing viral hemorrhagic septicemia, which can result in internal and external bleeding and significant mortality. HIRRV affects various flatfish species and other hosts in aquaculture settings.

Transmission occurs mainly through water and close contact, with hatcheries and high-density systems presenting increased risk. Disease dynamics are influenced by water temperature, stress, and crowding. Diagnosis relies on molecular assays (such as RT-PCR), virus isolation, and serology. Control measures focus on biosecurity, surveillance, movement controls, and vaccination where available.