Coronavirus: The family that has Shaken up the world

Posted On:19 March 2020

Coronavirus has been trending in the news ever since a member of this family has taken over the globe by causing a pandemic situation.

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Most of us are familiar with this term because either we have heard about it on the news or from our known ones. But when it comes to the masses, only a few know about this family as the people have remained oblivious towards them since their discovery. So in this article, we will try to learn about this family more by exploring a little.

Like any other family of viruses, coronavirus is also identified as a family of closely related viruses that cause potentially deadly diseases in mammals and birds. There are many different types of coronaviruses, out of which 7 are known to cause illnesses in humans where they spread via droplets of respiratory fluid.

But when did it all start?

The family description dates back to the 1960s, when in 1965, Tyrrell and Bynoe discovered a novel virus that was found to cause common cold in a human adult. Therefore, in the late 1960s when different scientists reported several morphologically similar strains, they were all clubbed together into this new group of viruses, named as Coronavirus. The virus gets its name from the Latin Word Corona, meaning crown, which refers to the characteristic appearance reminiscent of a crown of sugary-proteins the projects from the envelope surrounding the particle.

With a diameter of around 120nm, the virus appears as a large pleomorphic spherical particle having bulbous surface projections. The morphology of the virus includes four main structural proteins- a viral envelope (E); the spike (S), which forms the club-shaped protrusions; membrane proteins (M) and the nucleocapsid(N), which are bound to positive sense single-stranded RNA genome in a continuous beads-on-a string type conformation. Using the structural proteins, the virus enters the host cells where it establishes an infection, replicate, assemble its genome and then releases its progeny out of the host cell by exocytosis.  The coronavirus has the longest genome of any RNA-based virus as a single strand of nucleic acid is roughly 26,000 to 32,000 bases long.

The coronavirus has the highest known frequency of recombination of any positive-strand RNA virus, promiscuously combining genetic information from different sources when a host is infected with multiple coronaviruses. Therefore, these can mutate/change at a much faster rate and this property has made them a threat for the virology community.

The family of coronavirus has four known genuses, named Alphacoronavirus, Betacoronavirus, Gammacoronavirus , and Deltacoronavirus.  The first two only infect mammals, including bats, pigs, cats and humans. Gammacoronavirus mostly infects birds, while Deltacoronavirus can infect both birds and mammals. The virus can give rise to a variety of symptoms in different animals. While some strains cause diarrhea in pigs & cows, other can cause upper respiratory tract disease in chickens.  

The epidemiology studies of this virus reveals that in temperate climates, the virus causes respiratory coronavirus infections more often in the winter and spring than in the summer and fall.

In humans, Coronavirus vary significantly in terms of pathogenicity. Some can kill more than 30% of those infected (such as MERS-CoV) while some are relatively harmless, causing common cold. There are 7 known strains of human coronavirus, with the latest discovered after causing the pandemic COVID-19. These seven strains are known as follows:
1.    Human Coronavirus 229E (HCoV-229E), identified in the 1960s
2.    Human Coronavirus OC43 (HCoV-OC43), identified in the 1960s
3.    Severe acute respiratory syndrome coronavirus (SARS-CoV), identified in 2003
4.    Human Coronavirus NL63 (HCoV-NL63), identified in 2004
5.    Human Coronavirus HKU1, identified in 2005
6.    Middle East Respiratory syndrome-related coronavirus (MERS-CoV), previously known as HCoV-EMC, identified in 2012
7.    Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), previously known as 2019-nCoV, identified in 2019

Out of these 7 human coronavirus strains, only 3 (SARS-CoV-2, MERS-CoV & SARS-CoV) are known to cause severe infections and have an history of causing major disease outbreaks leading to many human deaths. 

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SARS-CoV causing the first major Outbreak-Severe acute respiratory syndrome (SARS)

SARS first emerged in 2002-2003 as the novel coronavirus (SARS-CoV) from southern china, spread throughout the world with quantifiable speed. The source of the virus has never been clear, but they are presumed to have been emerged from civets, that were being sold in live animal markets as exotic food. The first case of human infected with SARS can be traced back to the Chinese province of Guangdong in 2002, from where it spread worldwide.

The disease was declared pandemic, when more than 8000 cases were reported worldwide, including Canada and the United States, and more than 800 deaths were registered by mid-2003.

The SARS-CoV is considered more pathogenic among its peers, as it can infect both the upper and the lower respiratory system.

Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

The MERS virus was first detected in Jordan and Saudi Arabia in 2012 when people displayed symptoms of fever, cough and shortness of breath. In several countries, the evidences points at the dromedary camels as the suspected animal source for the virus. The transmission from animal to human is still not clear, though.

According to the WHO, there are around 2500 cases of identified infection in 27 countries since its initial outbreak, with nearly 860 deaths being registered in total.

Newly identified novel Coronavirus- SARS-CoV-2 that causes COVID-19

SARS-CoV-2 was reported in late 2019, in Wuhan, China and has since extensively spread to several countries worldwide. This newly identified coronavirus causes COVID-19, which has been declared by the WHO as a pandemic disease for taking up to approximately 8000 lives. This virus, earlier named 2019-nCoV, was renamed to SARS-CoV2 after it was found similar to the other variant, the SARS-CoV.
The virus is suspected to have originated from bats as it is very similar to a bat coronavirus. However, there is no documented cases of direct bat-human transmission, suggesting that an intermediate host is likely involved between bats and humans.

But do you know why the COVID-19 became pandemic within such a short span?

Professor Peter Piot, the man behind the joint discovery of Ebola, says that COVID-19 has a much greater potential of spreading around the globe than the previous epidemics, like Ebola. The reason he shares is that unlike Ebola, COVID-19 is caused by a respiratory transmitted virus that has a high pathogenicity. So, you have a higher chance of catching the disease just by talking to someone infected. Also, the symptoms shown by COVID-19 can be misinterpreted as a regular flu and this can fuel up the transmission process due to mere negligence.

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Till date, there has been no specific drug devised for treating coronavirus infections like SARS, MERS or COVID-19. However, such infections can be controlled by regularly monitoring the symptomatic patients and treating the positive ones with proper medication. For the careful transportation of the virus specimen, the CDC recommends collecting the suspected samples in the Viral Transport Medium and then performing RT-PCR for the confirmation of the disease. A proper care and hygiene has become of an importance today.