Coronaviruses, which belong to the subfamily Coronavirinae in the family Coronaviridae ( see  phylogeny), are enveloped RNA viruses that infect and cause disease in a broad array of animals and humans. Human coronaviruses (HCoV) were first identified in the 1960s from the nasal cavities of patients with the common cold. About 30% of common colds are caused by two human coronaviruses - OC43 and 229E. Coronavirus cold- or flu-like symptoms usually set in from two to four days after coronavirus infection, and they are typically mild. Symptoms include sneezing, runny nose, fatigue, cough, fever (rare), sore throat and eventually exacerbated asthma.
Virus particles range from 70 to 120 nm in diameter and are surrounded by characteristic spike-shaped glycoproteins. Coronaviruses contain a large single-stranded, positive-sense RNA genome, which range from 25.5 to 32 kb in length. The order of essential structural genes is remarkably well-conserved: all coronaviruses encode the replicase–transcriptase (gene 1), spike, envelope, membrane and nucleocapsid proteins. The positive strand RNA genome is infectious, i.e. virus can be rescued by transfecting permissive cells with the purified genome.
Two novel coronaviruses have emerged in humans in the twenty-first century:
- SARS-CoV (severe acute respiratory syndrome coronavirus). The SARS-CoV epidemic was recognized in early 2003 and caused 10–50% mortality in infected individuals, depending on their age. SARS-CoV probably originated in bats. Many of these viruses infect various bats and other animal species, and several are phylogenetically similar to known pathogenic human coronaviruses, which suggests that additional emergence events are highly likely to occur.
- MERS-CoV (Middle East respiratory syndrome coronavirus) which causes ~50% mortality in patients who seek medical attention, is transmissible on close contact and has caused transmission clusters and cases in several countries, including Saudi Arabia, Jordan, Qatar and the United Kingdom. Bat species have been implicated as reservoirs of MERS-CoV, but these species are distinct from those that are thought to have been involved in the emergence of SARS-CoV.
Last update: Friday, December 18, 2020
|