Coronaviruses are a group of viruses that cause diseases in mammals and birds. In humans, the viruses cause respiratory infections – including the common cold – which are typically mild. Rarer forms such as SARS, MERS and the novel coronavirus causing the 2019–20 Wuhan coronavirus outbreak can be lethal. In cows and pigs coronaviruses cause diarrhea. In chickens they cause an upper respiratory disease. There are no vaccines or antiviral drugs that are approved for prevention or treatment.
Coronaviruses are viruses in the subfamily Orthocoronavirinae in the family Coronaviridae, in the order Nidovirales. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and with a nucleocapsid of helical symmetry. The genomic size of coronaviruses ranges from approximately 26 to 32 kilobases, the largest for an RNA virus.
The name "coronavirus" is derived from the Latin corona, meaning crown or halo, which refers to the characteristic appearance of the virus particles (virions): they have a fringe reminiscent of a royal crown or of the solar corona.