Betacoronavirus

Betacoronavirus is a genus of enveloped, positive-sense single-stranded RNA viruses in the subfamily Coronavirinae, family Coronaviridae, order Nidovirales. The genus includes four phylogenetic lineages, designated A, B, C and D. Members infect a range of mammals, including humans, and are found worldwide. In humans, several betacoronaviruses cause respiratory illness of varying severity. Notable examples are HCoV-OC43 and HCoV-HKU1 (lineage A), which frequently cause mild upper-respiratory infections; SARS-CoV (lineage B) caused the 2002–2003 outbreak; MERS-CoV (lineage C) emerged in 2012; and SARS-CoV-2 (lineage B) emerged in 2019 and is responsible for COVID-19.

Genome and structure: Betacoronaviruses possess a large, roughly 27–32 kb positive-sense RNA genome. The genome encodes replicase proteins in ORF1a/1b, followed by structural proteins S (spike), E (envelope), M (membrane) and N (nucleocapsid), with additional accessory genes. The Spike protein mediates receptor binding and entry into host cells.

Host range, transmission, and evolution: Bats are the natural reservoir, with spillover to humans often involving intermediate hosts. Receptor usage varies; SARS-CoV and SARS-CoV-2 bind to ACE2, while MERS-CoV uses DPP4. Diseases range from mild colds to severe pneumonia and death. Coronaviruses exhibit genetic recombination and proofreading mechanisms, contributing to evolution, host range, and emergence of new pathogens.