The human coronaviruses (hCoVs), members of the family Coronaviridae, are enveloped RNA viruses that affect humans, mammals and birds, causing both acute and chronic illnesses.
Four of the seven known human coronaviruses usually cause a mild coryzal illness only, these are HKU1, NL63, OC43, and 229E .
Furthermore, there are now three much more virulent, zoonotic strains of coronavirus, that cause respiratory disease, and may be fatal, consisting of severe acute respiratory syndrome coronavirus (SARS-CoV-1), Middle East respiratory syndrome coronavirus (MERS-CoV), and most recently, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) .
The coronaviruses are found in the subfamily Coronavirinae (of the Coronaviridae family) within the order Nidovirales. There are four genera in the Coronavirinae subfamily: Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus .
All pathogenic human coronaviruses are from the Betacoronavirus genus, except CoV-229E and CoV-NL63, which are both alphacoronaviruses .
History and etymology
The first coronavirus was identified in 1966 by Tyrell and Bynoe, in individuals with the common cold .
The name coronavirus is derived from the Latin term 'corona' meaning crown, and the similarity to a solar corona. It derives from the morphology of the individual virion particles, which possess spiky protrusions arising from their surfaces, as seen on electron microscopy .