Coronaviruses are a group of related virusesthat cause diseases in mammals and birds. In humans, coronaviruses cause respiratory tract infections that can be mild, such as some cases of the common cold (among other possible causes, predominantly rhinoviruses), and others that can be lethal, such as SARS, MERS, and COVID-19. Symptoms in other species vary: in chickens, they cause an upper respiratory tract disease, while in cows and pigs they cause diarrhea. There are yet to be vaccines or antiviral drugs to prevent or treat human coronavirus infections.

Orthocoronavirinae
Transmission electron micrograph (TEM) of avian infectious bronchitis virus
Illustration of the morphology of coronaviruses; the club-shaped viral spike peplomers, colored red, create the look of a corona surrounding the virionwhen observed with an electron microscope.
Virus classification
(unranked):	Virus
Realm:	Riboviria
Phylum:	incertae sedis
Order:	Nidovirales
Family:	Coronaviridae
Subfamily:	Orthocoronavirinae
Genera[1]
Alphacoronavirus Betacoronavirus Gammacoronavirus Deltacoronavirus
Synonyms[2][3][4]
Coronavirinae

Coronaviruses constitute the subfamilyOrthocoronavirinae, in the family Coronaviridae, order Nidovirales, and realm Riboviria.^[5][6] They are enveloped viruses with a positive-sense single-stranded RNA genome and a nucleocapsid of helical symmetry. The genome size of coronaviruses ranges from approximately 27 to 34 kilobases, the largest among known RNA viruses.^[7] The name coronavirus is derived from the Latin corona, meaning "crown" or "halo", which refers to the characteristic appearance reminiscent of a crown or a solar corona around the virions (virus particles) when viewed under two-dimensional transmission electron microscopy, due to the surface being covered in club-shaped protein spikes.