Aquareoviruses

Aquareoviruses are a genus of double-stranded RNA viruses in the family Reoviridae, order Reovirales. They primarily infect aquatic animals, especially teleost fish, and have been associated with disease outbreaks in aquaculture. The viruses are nonenveloped with icosahedral symmetry and possess a segmented dsRNA genome.

The genome is composed of several dsRNA segments that encode structural and nonstructural proteins. Replication occurs in the cytoplasm of infected cells, and transcription of viral mRNA is carried out by a virion-associated RNA-dependent RNA polymerase. Viral genome segments can reassort during co-infection, contributing to genetic diversity.

Aquareoviruses primarily infect fish species and are of significant concern in aquaculture. Hosts include domesticated and wild freshwater and marine fish such as grass carp, carp, koi, and other teleosts. Disease manifestations reported in outbreaks range from hemorrhagic enteritis and gill pathology to growth retardation and high mortality, particularly in juvenile fish and in hatchery environments. Environmental factors like water temperature and stress can influence disease emergence and severity.

Transmission is mainly horizontal, through contaminated water, feed, or hatchery equipment; the role of vertical transmission is less clearly defined. Diagnosis relies on molecular methods such as RT-PCR and sequencing, as well as virus isolation in suitable fish cell lines where feasible and serological assays in some settings. Control measures emphasize biosecurity, water quality management, and vaccination programs in certain regions; vaccines against grass carp reovirus have been developed and implemented in some aquaculture operations.

Taxonomically, Aquareovirus is a recognized genus within Reoviridae, comprising several species. The best-characterized member is grass carp reovirus, a pathogen of economic importance in aquaculture. Aquareoviruses are not known to infect humans.