Corona Virus
Coronavirus
Coronaviruses are a group of
relatedvirusesthat cause diseases inmammalsandbirds. In humans, coronaviruses causerespiratorytract infectionsthat can range frommildtolethal.
Mild illnesses include some cases of thecommoncold(which has other possible causes,predominantlyrhinoviruses), while more lethal varieties can causeSARS,MERS, andCOVID-19. Symptoms in other species vary: in chickens, they cause anupperrespiratory tract disease, while in cows andpigs
they causediarrhea. There are yet to bevaccinesorantiviral drugsto prevent or treat human coronavirus infections.
Discovery
Coronaviruses were first discovered in the 1930s when an acute respiratory infection of domesticated chickens was shown to be caused byinfectiousbronchitis virus(IBV).Arthur Schalk and MC Hawn described in 1931 a newrespiratory infection ofchickensinNorth Dakota. The infection of new-born chicks was characterized by gasping and listlessness. The mortality rate of the chicks was 40–90%. In 1937, Fred Beaudette and Charles Hudson reported that they had successfully isolated and cultivated the infectious bronchitis virus which caused the disease. In the 1940s, two more animal coronaviruses,mousehepatitis virus(MHV) andtransmissiblegastroenteritis virus(TGEV), were isolated. It was not realized at the time that these three different viruses wererelated.
Human coronaviruses were discovered in the 1960s.The earliest ones studied were from human patients with thecommon cold, which were later namedhuman coronavirus 229Eandhumancoronavirus OC43.They were first imaged byScottishvirologistJune Almeidaat St. Thomas Hospital in London. Other human coronaviruses have since been identified, includingSARS-CoVin 2003,HCoVNL63in 2004,HKU1in 2005,MERS-CoVin 2012,
andSARS-CoV-2in 2019. Most of thesehave involved seriousrespiratory tract infections.
Etymology
The name "coronavirus" is derived from Latincorona,meaning "crown" or "wreath", itself a borrowing fromGreek "garland, wreath". The name was first used in 1968 by an informal group of virologists in thejournalNatureto designate the new family of viruses. The name refers to the characteristic appearance ofvirions(the infective form of the virus) byelectronmicroscopy,which have a fringe of large,bulbous
surface projections creating an image reminiscent of a crown or of asolar corona. Thismorphologyis created by the viral spikepeplomers, which areproteinson the surface of the virus.
Structure
Cross-sectional model of a coronavirus
Coronaviruses are largepleomorphicspherical particles with bulbous surface projections. The average diameter of the virus particles is around 120nm. The diameter of the envelope is ~80 nm and thespikesare ~20 nm long. The envelope of the virus in electron micrographs appears as a distinct pair of electron dense shells.
Theviral envelopeconsists of alipid bilayerwhere the membrane (M), envelope (E) and spike (S)structural proteinsare anchored.A subset of coronaviruses (specifically the members of
betacoronavirussubgroup A) also have a shorter spike-like surface protein calledhemagglutininesterase(HE).
Inside the envelope, there is thenucleocapsid, which is formed from multiple copies of the nucleocapsid
(N) protein, which are bound to the positive-sense single-stranded RNAgenome in a continuousbeads-on-a-stringtype conformation.The lipid bilayer envelope, membrane proteins, and nucleocapsid protect the virus when it is outside the host cell.
Transmission
The interaction of the coronavirus spike protein with its complementhost cell receptoris central in determining thetissue tropism,infectivity, andspeciesrangeof the virus. TheSARS coronavirus, for example, infects human cells by attaching to theangiotensin-converting enzyme 2(ACE2) receptor.
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