infections – including the cold – which are typically mild. Rarer forms like SARS, MERS and therefore the novel coronavirus
causing the 2019–20 Wuhan coronavirus outbreak are often lethal. In cows and pigs coronaviruses cause diarrhea. In chickens they
cause an upper respiratory illness . There are not any vaccines or antiviral drugs that are approved for prevention or treatment.
Coronaviruses are viruses within the subfamily Orthocoronavirinae within the family Coronaviridae, within 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 most important for an RNA virus.
The name "coronavirus" springs from the Latin corona, meaning crown or halo, which refers to the characteristic appearance
of the virus particles : they need a fringe like a royal crown or of the solar corona.
Discovery
Coronaviruses were discovered within the 1960s. The earliest ones discovered were infectious bronchitis virus in chickens and two
viruses from the nasal cavities of human patients with the 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 those are involved in serious
respiratory tract infections.
Name and morphology
The name "coronavirus" springs from the Latin corona and therefore the Greek, meaning crown or halo. This refers to the characteristic
appearance of virions by microscopy , which have a fringe of huge , bulbous surface projections creating a picture
reminiscent of a royal crown or of the solar corona. This morphology is made by the viral spike peplomers, which are proteins
that populate the surface of the virus and determine host tropism.
Proteins that contribute to the general structure of all coronaviruses are the spike, envelope, membrane, and nucleocapsid . In the
specific case of the SARS coronavirus, an outlined receptor-binding domain on S mediates the attachment of the virus to its
cellular receptor, angiotensin-converting enzyme 2 . Some coronaviruses even have a shorter spike-like protein called
hemagglutinin esterase . which is lacking in RNA-dependent RNA polymerase enzymes alone.
The RNA genome is replicated and an extended polyprotein is made , where all of the proteins are attached. Coronaviruses have a
non-structural protein – a protease – which is in a position to separate the proteins within the chain. this is often a sort of genetic economy for the
virus, allowing it to encode the best number of genes during a small number of nucleotides.
Transmission
Human to human transmission of coronaviruses is primarily thought to occur among close contacts via respiratory droplets
generated by sneezing and coughing.
Taxonomy
Genus: Alphacoronavirus; type species: Alphacoronavirus 1 they'll be considerably older than this. Another estimate places
the most recent common ancestor of all coronaviruses around 8100 BCE. The MRCA of Alphacoronavirus, Betacoronavirus,
Gammacoronavirus, and Deltacoronavirus are placed at about 2400 BCE, 3300 BCE, 2800 BCE and 3000 BCE,
respectively. It appears that bats and birds, the warm-blooded flying vertebrates, are ideal hosts for the coronavirus gene source
to fuel coronavirus evolution and dissemination.
Bovine coronavirus and canine respiratory coronavirus diverged from a standard ancestor in 1951. Bovine coronavirus and
human coronavirus OC43 diverged in 1899. Bovine coronavirus diverged from the equine coronavirus species at the top of the
18th century. Another estimate suggests that human coronavirus OC43 diverged from bovine coronavirus in 1890.
The MRCA of human coronavirus OC43 has been dated to the 1950s.
Middle East respiratory syndrome coronavirus, although associated with several bat species, appears to possess diverged from these
several centuries ago.
The human coronavirus NL63 and a bat coronavirus shared an MRCA 563–822 years ago.
The most closely related bat coronavirus and therefore the SARS coronavirus diverged in 1986. A path of evolution of the SARS virus and
keen relationship with bats are proposed. The authors suggest that the coronaviruses are coevolved with bats for a
long time and therefore the ancestors of SARS virus first infected the species of the genus Hipposideridae, subsequently spread to species
of the Rhinolophidae then to civets, and eventually to humans.
Alpaca coronavirus and human coronavirus 229E diverged before 1960.
Human coronaviruses
Coronaviruses are believed to cause a big percentage of all common colds in human adults and youngsters . Coronaviruses
cause colds with major symptoms, e.g. fever, throat swollen adenoids, in humans primarily within the winter and early spring
seasons. Coronaviruses can cause pneumonia, either direct viral infection or a secondary bacterial pneumonia and that 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, features a unique pathogenesis because it causes
both upper and lower tract infections.
The coronaviruses HCoV-229E, -NL63, -OC43, and -HKU1 continually circulate within the human population and cause respiratory
infections in adults and youngsters world-wide.
Severe acute respiratory syndrome
In 2003, following the outbreak of severe acute respiratory syndrome which had begun the prior year in Asia, and secondary
cases elsewhere within the world, the planet Health Organization issued a handout stating that a completely unique coronavirus identified by variety of laboratories was the causative agent for SARS. The virus was officially named the SARS coronavirus . Over 8,000
people were infected, about 10% of whom died. the planet Health Organization issued a worldwide alert soon after. The WHO
update on 28 September 2012 stated that the virus didn't seem to pass easily from person to person. However, on 12 May 2013,
a case of human-to-human transmission in France was confirmed by the French Ministry of Social Affairs and Health. In
addition, cases of human-to-human transmission are reported by the Ministry of Health in Tunisia. Two confirmed cases
involved people that appeared to have caught the disease from their late father, who became ill after a visit to Qatar and Saudi
Arabia. Despite this, it appears that the virus has trouble spreading from human to human, as most people who are infected
do not transmit the virus. By 30 October 2013, there have been 124 cases and 52 deaths in Saudi Arabia .
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