Coronaviridae

Coronaviridae is a family of enveloped, positive-sense single-stranded RNA viruses in the order Nidovirales. They infect birds and mammals, including humans, and are characterized by spike glycoproteins that project from the virion surface, producing a crown-like appearance under electron microscopy.

Virions are roughly 80–160 nanometers in diameter and have a helical nucleocapsid enclosed by a lipid envelope. The genome is a single, positive-sense RNA molecule of about 27 to 32 kilobases, among the largest for RNA viruses. The genome organization includes ORF1a/1b, encoding polyproteins pp1a/pp1ab, and a set of structural and accessory genes expressed via subgenomic mRNAs.

Taxonomically, Coronaviridae includes subfamilies Letovirinae and Orthocoronavirinae; Orthocoronavirinae contains four genera: Alphacoronavirus, Betacoronavirus, Gammacoronavirus, and Deltacoronavirus. Hosts range from birds to a wide array of mammals. Notable human-infecting viruses include several in these genera, such as SARS-CoV, MERS-CoV, and SARS-CoV-2, as well as seasonal human coronaviruses like HCoV-229E, HCoV-NL63, HCoV-OC43, and HCoV-HKU1.

Replication begins with attachment to host receptors, fusion or endocytosis, and translation of viral replicase polyproteins. The replication complex forms on double-membrane vesicles in the cytoplasm. New virions assemble in the endoplasmic reticulum-Golgi intermediate compartment and are released by exocytosis. The group exhibits high genetic diversity and frequent recombination, contributing to host range and emergence.

Coronaviruses were first described in the 1960s. The family gained prominence through outbreaks of severe disease in humans, culminating in the global SARS-CoV-2 pandemic. Public health responses include surveillance, vaccination, and development of antiviral strategies. Taxonomy and classification continue to evolve with accumulating genomic data.