Coronaviruses are a group of RNA viruses that cause diseases in mammals and birds. In humans and birds, they cause respiratory tract infections that can range from mild to lethal. Mild illnesses in humans include some cases of the common cold, while more lethal varieties can cause SARS, MERS, and COVID-19. In cows and pigs they cause diarrhea, while in mice they cause hepatitis and encephalomyelitis. There are as yet no vaccines or antiviral drugs to prevent or treat human coronavirus infections.
Coronaviruses are members of the subfamily Orthocoronavirinae, in the family Coronaviridae, order Nidovirales, and realm Riboviria. The genome size of coronaviruses ranges from approximately 26 to 32 kilobases, one of the largest among RNA viruses. They have characteristic club-shaped spikes that project from their surface, which in electron micrographs create an image reminiscent of the solar corona, from which their name derives.
The name “coronavirus” is derived from Latin corona, meaning “crown” or “wreath”, itself a borrowing from Greek korṓnē, “garland, wreath”. The name was coined by June Almeida and David Tyrrell who first observed and studied human coronaviruses. This morphology is created by the viral spike peplomers, which are proteins on the surface of the virus.
The scientific name Coronavirus was accepted as a genus name by the International Committee for the Nomenclature of Viruses in 1971. As the number of new species increased, the genus was split into four genera, namely Alphacoronavirus, Betacoronavirus, Deltacoronavirus, and Gammacoronavirus in 2009. The common name coronavirus is used to refer to any member of the subfamily Orthocoronavirinae. As of 2020, 45 species are officially recognised.
The earliest reports of an illness caused by a coronavirus occurred in the late 1920s, when an acute respiratory infection of domesticated chickens emerged in North America.1 Arthur Schalk and M.C. Hawn in 1931 made the first detailed report which described a new respiratory infection of chickens in North Dakota. The infection of new-born chicks was characterized by gasping and listlessness with high mortality rates of 40–90%. Leland David Bushnell and Carl Alfred Brandly isolated the virus in 1933.