Coronaviruses are a group of viruses that cause diseases in mammals and birds. In humans, the virus causes respiratory infections which are typically mild including the common cold but rarer forms like SARS and MERS can be lethal. In cows and pigs, they may cause diarrhea, while in chickens it can cause an upper respiratory disease. There are no vaccines or antiviral drugs that are approved for prevention or treatment.
Coronaviruses are viruses in the subfamily Orthocoronavirinae in the family Coronaviridae, in the order Nidovirales. Coronaviruses are enveloped viruses with a positive-sense single-stranded RNA genome and with a nucleocapsid of helical symmetry. The genomic size of coronaviruses ranges from approximately 26 to 32 kilobases, the largest for an RNA virus.
The name “coronavirus” is derived from the Latin corona, meaning crown or halo, which refers to the characteristic appearance of the virus particles (virions): they have a fringe reminiscent of a royal crown or of the solar corona.
When was the first discovery of Coronavirus?
Coronaviruses were discovered in the 1960s; the earliest ones discovered were infectious bronchitis virus in chickens and two viruses from the nasal cavities of human patients with the common cold that were subsequently named human coronavirus 229E and human coronavirus OC43.
Other members of this family have since been identified, including SARS-CoV in 2003, HCoV NL63 in 2004, HKU1 in 2005, MERS-CoV in 2012, and 2019-nCoV in 2019; most of these have been involved in serious respiratory tract infections.
Coronavirus name and morphology
The name “coronavirus” is derived from the Latin corona and the Greek κορώνη (korṓnē, “garland, wreath”), meaning crown or halo. This refers to the characteristic appearance of virions (the infective form of the virus) by electron microscopy, which have a fringe of large, bulbous surface projections creating an image reminiscent of a royal crown or of the solar corona. This morphology is created by the viral spike (S) peplomers, which are proteins that populate the surface of the virus and determine host tropism.
Proteins that contribute to the overall structure of all coronaviruses are the spike (S), envelope (E), membrane (M) and nucleocapsid (N). In the specific case of the SARS coronavirus (see below), a defined receptor-binding domain on S mediates the attachment of the virus to its cellular receptor, angiotensin-converting enzyme 2 (ACE2). Some coronaviruses (specifically the members of Betacoronavirus subgroup A) also have a shorter spike-like protein called hemagglutinin esterase (HE).
What are the known Human Coronaviruses?
Coronaviruses are believed to cause a significant percentage of all common colds in human adults and children. Coronaviruses cause colds with major symptoms, e.g. fever, throat swollen adenoids, in humans primarily in the winter and early spring seasons. Coronaviruses can cause pneumonia, either direct viral pneumonia or a secondary bacterial pneumonia and they can also cause bronchitis, either direct viral bronchitis or a secondary bacterial bronchitis. The much publicized human coronavirus discovered in 2003, SARS-CoV which causes severe acute respiratory syndrome (SARS), has a unique pathogenesis because it causes both upper and lower respiratory tract infections.
There are four main sub-groupings of coronaviruses, known as alpha, beta, gamma, and delta.
The seven coronaviruses that can infect people are:
Common Human Coronaviruses
- 229E (alpha coronavirus)
- NL63 (alpha coronavirus)
- OC43 (beta coronavirus)
- HKU1 (beta coronavirus)
Other Human Coronaviruses
- MERS-CoV (the beta coronavirus that causes Middle East Respiratory Syndrome, or MERS)
- SARS-CoV (the beta coronavirus that causes severe acute respiratory syndrome, or SARS)
- 2019 Novel Coronavirus (2019-nCoV)
People around the world commonly get infected with human coronaviruses 229E, NL63, OC43, and HKU1.
Sometimes coronaviruses that infect animals can evolve and make people sick and become a new human coronavirus. Three recent examples of this are 2019-nCoV, SARS-CoV, and MERS-CoV.