Coronaviruses are RNA viruses that cause diseases in mammals and birds derived from Latin word corona which means ‘crown’, named by June Alimedia and David Tyrrell who first observed human coronaviruses.
Coronavirus cause respiratory tract infection in human that range from mild to lethal, mild illness include common cold while lethal verities cause MERS(middle east respiratory syndrome), SARS(severe acute respiratory syndrome) and COVID-19.
Constitute subfamily orthocoronavirinae. The virus is enveloped and has a positive sense single-stranded RNA genome and helical symmetry nucleocapsid.
Coronaviruses are among the largest virus, size ranges between 26-32 kilobases.
Arthur Schalk and M. C. Hawn in 1931 described a new respiratory infection of chicken in North Dakota. The mortality rate was 40-90% in new born chicks.
Six years later Fred Beaudette and Charles Hudson successfully isolate and cultivated IBV (infectious bronchitis virus) which cause disease.
In 1960s human coronaviruses were discovered. E. C. Kendall, Malcom Byone, and David Tyrrell working at British Medical Research Council isolated a novel common cold virus B814 from a boy. In n1965 Tyrell and Byone cultivated the novel virus in organ culture of human embryonic trachea by serially passing through it, the virus cannot be cultivated by standard techniques used for rhinoviruses and other common cold viruses.
At the same time Dorothy Hamre and John Procknow at the University of Chicago from a medical student isolated a novel cold virus 229E grew in kidney tissue culture.
In 1967 June Almeida imaged this two novel strain by electron microscopy and said that the two strains were morphologically related by their club-like spikes.
Many human coronaviruese have been identified SARS (2003), MERS (2012) and SARS cov-2 (2019).
Large, spherical particles with bulbous surface projection
The virus diameter is around 125nm, envelope diameter is 85nm and the spikes are 20nm long.
The envelope is made up of lipid bilayer in which the membrane, envelope and spike structural protein are anchored in the ratio of 1:20:300(E:S:M).
A single particle on an average has 74 surface spikes.
The spikes are homotrimers of S protein composed S1 and S2 subunit. S protein is the class 1 fusion protein responsible for receptor binding and membrane fusion with the host cell.
S1 subunit forms head and has RBD (receptor binding domain), S2 forms the stem which anchor the spikes in the viral envelope and enable fusion on protease activation
E and M contribute in envelope formation and maintaining the shape.
Novel coronavirus is a new strain which has not been identified in humans yet.
Coronaviruses are zoonotic which means they transfer from animal to human. Example SARS cov was transmitted from civet cats to human and MERS cov from dromedary camels to humans. Many coronaviruses strains are circulating in animals have not infected humans.
Infection carriers shed the viruses into environment while sneezing, coughing or sometimes speaking.
When these droplets come in contact with other person it gets inside the body through mouth, nose and eyes.
Most common symptoms:
Less common symptoms:
Aches and pains
Loss of taste or smell
Chest pain or pressure
Difficulty breathing or shortness of breath
Loss of speech or movement
Prevention and Control
It is better to prevent from any disease than cure
Prevention of coronaviruses is to avoid being exposed to it
The major source of transmission is transfer of droplets, this can be controlled by respiratory hygiene
Following measures to be adopted to avoid transmission of these droplets
Always wash hand with soap and water for at least 20 second or if no dirty notice alcohol based rub can be used, especially after traveling or after sneezing, coughing and blowing nose
Avoid close contact with people who are sick or in contact with sick person because it may take few days to show symptoms and may be asymptomatic.
Wearing mask or cover moth with cloth when come contact with other people
Keeping a distance of at least 1 meter from other person
In any person doesn’t have cloth or mask covering their moth they should use tissue or under elbow while sneezing and frequently dispose tissue in the dustbin.
Regular cleaning and disinfection of the frequently touched surfaces i.e. Doorknobs, light switches, table, tapes
Precaution taken in hospitals for the patient and healthcare worker
Patient should be placed in a single room with proper ventilation if single rooms are not available the suspected patients should grouped together.
Health care staff should were proper medical mask, facial protection or eye protection to avoid contamination
In hospitals beds of the patient should be placed at least 1 meter apart
The equipment which are being shared among the patient should be disinfect after each use
Awareness should be generated among the patient, the general public families about the symptoms prevention and precautions