| Orthornavirae | |
|---|---|
| |
| Clockwise from top left: TEM of avian coronavirus, polio virus, bacteriophage Qβ, ebolavirus, tobacco mosaic virus, influenzavirus A, rotavirus, vesicular stomatitis virus. Center: phylogenetic tree of shared replication protein RdRp. | |
Virus classification 
| |
| (unranked): | Virus |
| Realm: | Riboviria |
| Kingdom: | Orthornavirae |
| Phyla and classes | |
Orthornavirae is a kingdom of viruses that have genomes made of ribonucleic acid (RNA), including genes which encode an RNA-dependent RNA polymerase (RdRp). The RdRp is used to transcribe the viral RNA genome into messenger RNA (mRNA) and to replicate the genome. Viruses in this kingdom share a number of characteristics which promote rapid evolution, including high rates of genetic mutation, recombination, and reassortment.
Viruses in Orthornavirae belong to the realm Riboviria. They are descended from a common ancestor that may have been a non-viral molecule that encoded a reverse transcriptase instead of an RdRp for replication. The kingdom is subdivided into five phyla that separate member viruses based on their genome type, host range, and genetic similarity. Viruses with three genome types are included: positive-strand RNA viruses, negative-strand RNA viruses, and double-stranded RNA viruses.
Many of the most widely known viral diseases are caused by members of this kingdom, including coronaviruses, the Ebola virus, influenza viruses, the measles virus, and the rabies virus, as well as the first virus ever discovered, tobacco mosaic virus. In modern history, RdRp-encoding RNA viruses have caused numerous disease outbreaks, and they infect many economically important crops. Most eukaryotic viruses, including most human, animal, and plant viruses, are RdRp-encoding RNA viruses. In contrast, there are relatively few prokaryotic viruses in the kingdom.