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| corona virus |
Coronaviruses are species in the genera of virus belonging to the subfamily Coronavirinae in the family Coronaviridae. Coronaviruses are enveloped viruses with a positive-sense RNA genome and with a nucleocapsid of helical symmetry. The genomic size of coronaviruses ranges from approximately 26 to 32 kilobases, extraordinarily large for an RNA virus. The name "coronavirus" is derived from the Latin corona, meaning crown or halo, and refers to the characteristic appearance of virions under electron microscopy (E.M.) with a fringe of large, bulbous surface projections creating an image reminiscent 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. Coronaviruses are grouped in the order Nidovirales, named for the Latin nidus, meaning nest, as all viruses in this order produce a 3' co-terminal nested set of subgenomic mRNA's during infection.
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
Coronaviruses primarily infect the upper respiratory and gastrointestinal tract of mammals and birds. Four to five different currently known strains of coronaviruses infect humans. The most publicized human coronavirus, SARS-CoV which causes SARS, has a unique pathogenesis because it causes both upper and lower respiratory tract infections and can also cause gastroenteritis. Coronaviruses are believed to cause a significant percentage of all common colds in human adults. Coronaviruses cause colds in humans primarily in the winter and early spring seasons. The significance and economic impact of coronaviruses as causative agents of the common cold are hard to assess because, unlike rhinoviruses (another common cold virus), human coronaviruses are difficult to grow in the laboratory.
In chickens, the infectious bronchitis virus (IBV), a coronavirus, targets not only the respiratory tract but also the uro-genital tract. The virus can spread to different organs throughout the chicken.
Coronaviruses also cause a range of diseases in farm animals and domesticated pets, some of which can be serious and are a threat to the farming industry. Economically significant coronaviruses of farm animals include porcine coronavirus (transmissible gastroenteritis coronavirus, TGE) and bovine coronavirus, which both result in diarrhea in young animals. Feline Coronavirus: two forms, Feline enteric coronavirus is a pathogen of minor clinical significance, but spontaneous mutation of this virus can result in feline infectious peritonitis (FIP), a disease associated with high mortality. There are two types of canine coronavirus (CCoV), one that causes mild gastrointestinal disease and one that has been found to cause respiratory disease. Mouse hepatitis virus (MHV) is a coronavirus that causes an epidemic murine illness with high mortality, especially among colonies of laboratory mice. Prior to the discovery of SARS-CoV, MHV had been the best-studied coronavirus both in vivo and in vitro as well as at the molecular level. Some strains of MHV cause a progressive demyelinating encephalitis in mice which has been used as a murine model for multiple sclerosis. Significant research efforts have been focused on elucidating the viral pathogenesis of these animal coronaviruses, especially by virologists interested in veterinary and zoonotic diseases
Replication of Coronavirus begins with entry to the cell which takes place in the cytoplasm in a membrane-protected microenvironment. Upon entry to the cell the virus particle is uncoated and the RNA genome is deposited into the cytoplasm. The Coronavirus genome has a 5’ methylated cap and a 3’polyadenylated tail. This also allows the RNA to attach to ribosomes for translation. Coronaviruses also have a protein known as a replicase encoded in its genome which allows the RNA viral genome to be transcribed into new RNA copies using the host cells machinery. The replicase is the first protein to be made as once the gene encoding the replicase is translated the translation is stopped by a stop codon. This is known as a nested transcript, where the transcript only encodes one gene it is monocistronic. The RNA genome is replicated and a long polyprotein is formed, where all of the proteins are attached. Coronaviruses have a non-structural protein called a protease which is able to separate the proteins in the chain. This is a form of genetic economy for the virus allowing it to encode the greatest number of genes in a small number of nucleotides.
Coronavirus transcription involves a discontinuous RNA synthesis (template switch) during the extension of a negative copy of the subgenomic mRNAs. Basepairing during transcription is a requirement. Coronavirus N protein is required for coronavirus RNA synthesis, and has RNA chaperone activity that may be involved in template switch. Both viral and cellular proteins are required for replication and transcription. Coronaviruses initiate translation by cap-dependent and cap-independent mechanisms. Cell macromolecular synthesis may be controlled after Coronavirus infection by locating some virus proteins in the host cell nucleus. Infection by different coronaviruses cause in the host alteration in the transcription and translation patterns, in the cell cycle, the cytoskeleton, apoptosis and coagulation pathways, inflammation, and immune and stress responses
Following the high-profile publicity of SARS outbreaks, there has been a renewed interest in coronaviruses among virologists. For many years, scientists knew about only two human coronaviruses (HCoV-229E and HCoV-OC43). The discovery of SARS-CoV added a third human coronavirus.
By the end of 2004, three independent research labs reported the discovery of a fourth human coronavirus. It has been named NL63, NL, and the New Haven coronavirus by different research groups. The three labs are still arguing over which one discovered the virus first and has the right to name it.
Early in 2005, a research team at the University of Hong Kong reported finding a fifth human coronavirus in two patients with pneumonia. They named it Human coronavirus HKU1.
In September 2012, what is believed to be a sixth new type of coronavirus, tentatively referred to as Novel Coronavirus 2012, being like SARS (but still distinct from it and from the common-cold coronavirus) was discovered in Qatar and Saudi Arabia. The World Health Organisation has accordingly issued a global alert and an interim case definition to help countries to strengthen health protection measures against it. The WHO update on 28 September 2012 said that the virus did not seem to pass easily from person to person. However, on May 12, 2013, a case of contamination from human to human in France was confirmed by the French Ministry of Social Affairs and Health. In addition, cases of person-to-person transmission have been reported by the Ministry of Health in Tunisia. Two confirmed cases seem to have caught the disease from their late father, who became ill after a visit to Qatar and Saudi Arabia. So far there have been twenty-two cases and ten deaths in eastern Saudi Arabia. After the Dutch Erasmus Medical Centre sequenced the virus, the virus was given a new name, Human Corona Virus-Erasmus Medical Centre (HCoV-EMC). The final name for the virus is: Middle East respiratory syndrome coronavirus (MERS-CoV).
Listing of human coronaviruses
- HCoV-229E
- HCoV-OC43
- SARS-CoV
- Human Coronavirus NL63 (HCoV-NL63, New Haven coronavirus)
- Human coronavirus HKU1
- Middle East respiratory syndrome coronavirus (MERS-CoV), previously known as Novel coronavirus 2012 and HCoV-EMC
(listed following their estimated economical importance)
- Infectious bronchitis virus (IBV) causes avian infectious bronchitis.
- Porcine coronavirus (transmissible gastroenteritis coronavirus of pigs, TGEV).
- Bovine coronavirus (BCV), responsible for severe profuse enteritis in of young calves.
- Feline coronavirus (FCoV) causes mild enteritis in cats as well as severe Feline infectious peritonitis (other variants of the same virus).
- the two types of canine coronavirus (CCoV) (one causing enteritis, the other found in respiratory diseases).
- Turkey coronavirus (TCV) causes enteritis in turkeys.
- Ferret enteric coronavirus causes epizootic catarrhal enteritis in ferrets
- Genus: Alphacoronavirus; type species: Alphacoronavirus 1
- Species: Alpaca coronavirus, Alphacoronavirus 1, Human coronavirus 229E, Human Coronavirus NL63, Miniopterus Bat coronavirus 1, Miniopterus Bat coronavirus HKU8, Porcine epidemic diarrhea virus, Rhinolophus Bat coronavirus HKU2, Scotophilus Bat coronavirus 512
- Genus Betacoronavirus; type species: Murine coronavirus
- Species: Betacoronavirus 1, Human coronavirus HKU1, Murine coronavirus, Pipistrellus Bat coronavirus HKU5, Rousettus Bat coronavirus HKU9, Severe acute respiratory syndrome-related coronavirus, Tylonycteris Bat coronavirus HKU4, MERS-CoV, HCoV-OC43
- Genus Deltacoronavirus; type species: Bulbul coronavirus HKU11
- Species: Bulbul coronavirus HKU11, Munia coronavirus HKU13, Thrush coronavirus HKU12
- Genus Gammacoronavirus; type species: Avian coronavirus
- Species: Avian coronavirus, Beluga whale coronavirus SW1
