Coronavirus means crown—named for spikes under the microscope
Coronaviruses are related RNA viruses that infect mammals and birds. In people they cause airway illness from ordinary colds to deadly outbreaks. June Almeida and David Tyrrell coined the crown metaphor after seeing the halo of spike proteins; Nature printed the word in 1968.
In humans, these viruses attack the airways, producing anything from a mild cold to a lethal illness. Their genetic material is a single positive-sense strand of RNA, between about 26 and 32 kilobases long, one of the biggest genomes any RNA virus carries. Taxonomists place them in the subfamily Orthocoronavirinae; the genus name was accepted internationally in 1971 and later divided into four genera as species multiplied.
Animal infections were noticed first. In the late 1920s a new respiratory disease swept through domestic chickens in North America, and Arthur Schalk and M.C. Hawn described it in detail in 1931. Human strains turned up in the 1960s, partly through work at Britain's Common Cold Unit by E.C. Kendall, Malcolm Bynoe and David Tyrrell. In 1967 the Scottish virologist June Almeida, working with Tyrrell at St Thomas' Hospital in London, used electron microscopy to show that a chicken virus and two human cold viruses shared the same club-studded outline.
That outline gave the family its name, from the Latin for crown or wreath. A typical particle is roughly spherical and 80 to 120 nanometres across, with extremes from 50 to 200. Its fatty envelope carries three structural proteins in a ratio of about one envelope protein to 20 spike and 300 membrane proteins. An average particle bears 74 spikes, each about 20 nanometres long and built from three copies of the S protein, and the part called S1 decides which host cells the virus can enter.
Inside, copies of the nucleocapsid protein bind the RNA like beads on a string. Genetic studies published in 2021 suggested the most recent common ancestor of coronaviruses may date to an outbreak in East Asia some 21,000 to 25,000 years ago.
Source: Coronavirus
