Coronaviridae is a family of enveloped, positive-sense single-stranded RNA viruses best known for their crown-like appearance under electron microscopy. Particles are roughly spherical, typically 80–160 nm in diameter, and bear conspicuous protein spikes that project from the envelope. These features give the virions a solar corona–like outline and are responsible for virus attachment and entry into host cells. Early electron microscopic descriptions inspired the family name; the family is classified within the order Nidovirales. Overview and images

Structure and genome

Members of Coronaviridae have some of the largest RNA genomes among viruses, generally about 26–32 kilobases in length. The genome is single-stranded and of positive polarity, functioning as mRNA immediately after entry. Key structural proteins encoded near the 3' end include the spike (S), membrane (M), envelope (E), and nucleocapsid (N) proteins; many coronaviruses also express variable accessory proteins that modulate host responses. The nucleocapsid forms a helical ribonucleoprotein inside the envelope, a trait that helps distinguish the family. For a schematic of genes and proteins see genome maps.

Replication and cell biology

Replication occurs in the cytoplasm and involves synthesis of a large replicase polyprotein that is proteolytically processed into functional enzymes, including an RNA-dependent RNA polymerase and proofreading exonuclease. Coronaviruses employ a nested set of subgenomic messenger RNAs produced by discontinuous transcription to express structural and accessory genes. Infection commonly induces rearrangement of intracellular membranes to create replication compartments such as double-membrane vesicles. For mechanistic details and experimental findings, consult relevant reviews at technical resources.

Hosts, disease, and importance

The family infects a broad range of vertebrate hosts including mammals and birds. Some genera are primarily associated with specific groups: for example, several human coronaviruses cause respiratory illness ranging from common colds to severe respiratory syndromes. Animal coronaviruses can cause enteric, respiratory or systemic disease in livestock, companion animals and wildlife, with significant veterinary and economic impact. Zoonotic spillover from animal reservoirs has produced notable human outbreaks and global public-health responses; see outbreak summaries at public health pages.

Taxonomy and history

Coronaviruses were identified in the 1960s from human and avian respiratory infections and later grouped into a single family as microscopy, genetic and antigenic data accumulated. Modern taxonomy divides the family into subgroups and genera based on genome sequence and host range. Classification continues to be refined as new viruses are discovered in wildlife surveillance studies. Historical perspectives and taxonomic details are available at taxonomic authorities.

Detection, control and research

Diagnosis commonly uses molecular methods such as reverse transcription PCR and sequencing, supported by serology in some contexts. Control measures range from vaccination in animals and humans where available, to biosecurity and public-health interventions during outbreaks. Coronaviruses are a focus of ongoing research into virus evolution, host range determinants, antiviral drugs and vaccine technologies; further information and research portals can be found at research resources.

  • Key points: large RNA genome, envelope with spikes, wide host range.
  • Notable human pathogens include species that have caused severe respiratory illness.
  • Active surveillance in animals is important to detect potential zoonotic threats.