Some colds may be caused by a coronavirus, but the word coronavirus refers to a whole subfamily of viruses, called the Orthocoronavirinae. The subfamily is divided into 4 genera, whose names were inspired by the Greeks, Alphacoronavirus, Betacoronavirus, Deltacoronavirus, and Gammacoronavirus (sadly it is the alphabet and not the mythology). As of last year, 45 species have been recognized in the subfamily.
Coronaviruses all look the same, a spherical lipid bilayer with spike proteins that are unique to each species. The coronaviruses’ hereditary information is encoded in RNA (Ribonucleic Acid) instead of DNA (Deoxyribonucleic Acid) as in humans and is stored in the centre of the sphere packed with protective proteins. Even though coronaviruses have some of the largest genomes among RNA viruses, it only has 26.4 to 31.7 kilobases in its genome compared to humans with a genome size of 6200 megabases. Despite the simplicity of the coronaviruses, they can run amok among humans and animal populations.
Infectious bronchitis virus, causing gasping symptoms in chicks, was the first coronavirus identified in 1932. It was also the first coronavirus to have its genome completely sequenced in 1987. Only in 1965 the first human infecting coronavirus was discovered by the Common Cold Research Unit, unsurprisingly, causing cold symptoms. Currently, coronaviruses are known to infect various agricultural animals, pets, and wildlife. Bats appear to be the natural reservoir for most coronaviruses after research has shown the greatest variety of coronaviruses infecting bats. It is estimated that there may be 3200 different coronaviruses infecting bats.
Three different coronaviruses have recently caused serious outbreaks among humans namely the SARS outbreak between 2002 and 2003, MERS outbreaks in 2012, 2015 and 2018 and the current pandemic of Covid-19. The fatality rate for the respective diseases is 14%-20% for SARS, 37% for MERS and 2.2% for COVID-19. All of which are clearly more serious than a common cold.
Other know coronaviruses, their host, and some details regarding the disease they cause are listed below.
|Alphacoronavirus||FIPV (Feline Infectious Peritonitis Virus||Cats||Cats show mild, if any, symptoms of diarrhoea and/or mild upper respiratory tract symptoms. In some cats, the virus infects the white blood cells which results in a serious inflammatory reaction affecting the blood vessels.|
|PRCV (Porcine Respiratory Coronavirus)||Pigs||Results in a very mild cough if there are any symptoms.|
|TGEV (Transmissible Gastroenteritis Virus)||Pigs||Has a 100% mortality rate in week old piglets. It destroys cells in the lining of the intestines preventing the absorption of nutrients and water in victims.|
|Rh-BatCoV HKU2 (Rhinolophus Bat Coronavirus HKU2)||Bats|
|HCoV-NL63||Young Children and Immuno- compromised Individuals||Causes bronchitis, pneumonia, and croup.|
|HCoV-229E||Humans and bats||Common cold, could be serious when victims are co-infected with another pathogen.|
|PEDV (Porcine Epidemic Diarrhoea Virus)||Pigs||Has a 100% mortality rate in week old piglets. Results in severe diarrhoea.|
|Betacoronavirus||HCoV-OC43||Humans and cattle||Common cold|
|PHEV (Porcine Hemagglutinating Encephalomyelitis Virus)||Pigs||Mostly affect piglets younger than 4 weeks. Mortality close to 100%.|
|BCoV||Cattle||Mostly affects calves between a week and 3 months old. Symptoms include diarrhoea, dehydration, and anorexia.|
|MHV (Murine Hepatitis Virus)||Mice||Causes epidemics in colonies of laboratory mice with a high mortality rate. Causes encephalitis in the mice.|
|SARSr-CoV-1||Human||Caused 2002-2004 SARS outbreak.|
|SARSr-CoV-2||Human||Causing current COVID-19 pandemic.|
|Gammacoronavirus||SW1||Beluga Whale||Identified in 2008 in deceased male. Characterised by pulmonary disease and acute liver failure. Similar virus has been isolated from bottlenose dolphins.|
|TCoV (Turkey Coronavirus)||Turkeys||Causes acute enteric disease resulting in poor growth.|
|IBV (Infectious Bronchitis Virus)||Birds||Results in poor growth and reduced egg laying in chickens. Vaccination only partially effective due number of antigenic types of the virus.|
|Deltacoronavirus||MunCov HKU13||Munias (Mannikins)|
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