Betacoronaviruses

Betacoronaviruses are a genus of enveloped, positive-sense single-stranded RNA viruses in the subfamily Orthocoronavirinae, family Coronaviridae, order Nidovirales. They infect mammals and birds and can cause diseases ranging from mild respiratory illness to severe pneumonia and systemic effects. In humans, betacoronaviruses include some agents of common colds as well as important pathogens capable of causing outbreaks.

The genus is divided into four lineages (A, B, C, D). Notable human pathogens include SARS-CoV and SARS-CoV-2 (lineage B), which emerged in recent decades and are associated with severe respiratory disease; MERS-CoV (lineage C), linked to severe pneumonia and acute respiratory distress. Human coronaviruses HCoV-OC43 and HCoV-HKU1 belong to lineage A and typically cause mild respiratory infections. Other animal betacoronaviruses include bovine coronavirus and various murine and bat coronaviruses. The spike glycoprotein on the virion mediates entry into host cells, and receptor usage varies by virus: SARS-CoV and SARS-CoV-2 use ACE2, MERS-CoV uses DPP4, among others. Transmission occurs mainly through respiratory droplets and can involve aerosols in some settings; spillover from bat reservoirs, often with intermediate hosts, has been implicated in several human outbreaks.

Genetically, betacoronaviruses have large, non-segmented RNA genomes of roughly 27 to 32 kilobases. The genome features a replication-transcription complex encoded by ORF1a/1b, followed by structural genes for the spike (S), envelope (E), membrane (M), and nucleocapsid (N) proteins, with additional accessory proteins. Replication occurs in the cytoplasm, and the viruses are prone to genetic recombination, contributing to their evolution and host range.

Public health relevance stems from their capacity to cause epidemics and pandemics, as seen with SARS, MERS, and SARS-CoV-2, driving ongoing surveillance, vaccine development, and antiviral research.