Nidovirales is an order of enveloped, positive-strand RNA viruses which infect vertebrates and invertebrates. Host organisms include mammals, birds, reptiles, amphibians, fish, arthropods, molluscs, and helminths. The order includes the families Coronaviridae, Arteriviridae, Roniviridae, Tobaniviridae, and Mesoniviridae.

Member viruses have a viral envelope and a positive-sense, single-stranded RNA genome which is capped and polyadenylated. Nidoviruses are named for the Latin nidus, meaning nest, as all viruses in this order produce a 3' co-terminal nested set of subgenomic mRNAs during infection.

Virology

Structure

thumb|Comparison of [[genomes and proteomes of different families of nidoviruses]]

Nidoviruses have a viral envelope and a positive-sense, single-stranded RNA genome which is capped and polyadenylated.]]

The order Nidovirales can be divided into two clades depending on the size of the genome: those with large genomes (26.3–31.7 kilobases) which included the Coronaviridae and Roniviridae (the large nidoviruses) and those with small genomes (the small nidoviruses)—a clade that includes the distantly related Arteriviridae (12.7–15.7 kb).

The large nidoviruses encode both a 2'-O-methyltransferase and a 3'–5' exoribonuclease (ExoN)—the latter being very unusual for an RNA virus. They also encode a superfamily 1 helicase, uridylate-specific endonuclease (an enzyme unique to nidoviruses) and several proteases.

Nidoviruses as a group have the largest RNA genomes of viruses. The largest reported genomes for RNA viruses are Crassostrea gigas nidovirus (CGNV) and Pacific oyster nidoviirus 1 (PONV 1); they are biseqmented, ~64kb in size, and infect Pacific oysters. They are members of a widely distributed group of viruses that belong to the proposed family Megarnaviridae. that infect a planarian flatworm.

Taxonomy

The following suborders and families are recognized (-virineae denotes suborders and -viridae denotes families):

thumb|Taxonomy tree of the order Nidovirales

  • Abnidovirineae
  • Abyssoviridae
  • Arnidovirineae
  • Arteriviridae
  • Cremegaviridae
  • Gresnaviridae
  • Olifoviridae
  • Cornidovirineae
  • Coronaviridae
  • Mesnidovirineae
  • Medioniviridae
  • Mesoniviridae
  • Monidovirineae
  • Mononiviridae
  • Nanidovirineae
  • Nanghoshaviridae
  • Nanhypoviridae
  • Ronidovirineae
  • Euroniviridae
  • Roniviridae
  • Tornidovirineae
  • Tobaniviridae

See also

  • Animal viruses
  • Coronaviruses
  • Serpentoviruses

References

  • Nidovirales—ICTVdB—The Universal Virus Database, version 4.
  • NIH/MeSH
  • "The Nidoviruses"