Coronaviridae

The coronaviruses (order Nidovirales, family Coronaviridae, genus Coronavirus) are members of a family of large, enveloped, positivesense single-stranded RNA viruses that replicate in the cytoplasm of animal host cells (Siddell).

The genomes of coronaviruses range in length from 27 to 32 kb, the largest of any of the RNA viruses. The virions measure between about 100 and 140 nanometers in diameter. Most but not all viral particles show the characteristic appearance of surface projections, giving rise to the virus' name (corona, Latin = crown). These spikes extend a further 20 nanometers from the surface.

The Coronaviridae family has been divided up into three groups, originally on the basis of serological cross-reactivity, but more recently on the basis of genomic sequence homology (see online database ICTVdB). Groups 1 (canine, feline infectious peritonitis, porcine transmissible gastroenteritis and porcine respiratory viruses, human coronavirus 229E) and 2 (bovine, murine hepatitis, rat sialodacryoadenitis viruses, human coronavirus OC43) contain mammalian viruses, while group 3 contains only avian viruses (avian infectious bronchitis, turkey coronavirus).

In animals, coronaviruses can lead to highly virulent respiratory, enteric, and neurological diseases, as well as hepatitis, causing epizootics of respiratory diseases and/or gastroenteritis with short incubation periods (2–7 days), such as those found in SARS (Holmes). Coronaviruses are generally highly species-specific. In immunocompetent hosts, infection elicits neutralizing antibodies and cell-mediated immune responses that kill infected cells.