Coronavirus : An Introduction


As the whole world is under lockdown due to Coronavirus Disease 2019 (COVID19), I am writing this blog about the virus. Trust me, I am a biologist and will try to provide only scientific proven facts. So, all (or most) of us have seen in news and media that Covid 19 is a deadly virus disease and we have no cure for it.

I am not sure how many of you remember the severe acute respiratory syndrome (SARS) epidemic which started in 2002. I was 11 years old when SARS epidemic hit the China and some other countries. I vaguely remember that I wanted to attend India International Trade fair that year and warning were being issued about SARS. I don’t remember if it hit India and as a kid, I never bothered to figure out more at that time. I would just go with my routine of school, study and play as usual. Today, I found out, India had 3 patients of SARS back in 2002, who recovered later.

When this year Covid19 was declared pandemic, I immediately went into flashback mode and memory of SARS (Severe Acute Respiratory Syndrome) came back, Covid19 didn’t remind me of recent epidemics like, MERS (Middle East respiratory syndrome), Ebola or H1N1 and I don’t know why. I got curious to know if something is common in between SARS  2002 and COVID19. A little research led me to an answer of “YES”. SARS which happened in 2002 was also by a coronavirus, not the same though which we are encountering now. Also, MERS, epidemic which hit middle east in 2012 was by a coronavirus

For this blog I will try to focus on two things; What are corona viruses? and how different COVID19 is from diseases caused by other Coronaviruses

Coronaviruses belongs to the family of viruses called Coronaviridae and they typically affect respiratory tract of birds and mammals. The word corona means “Crown”, these coronaviruses have crown like shape and spike like proteins which attach to host cells. Coronaviruses have zoonotic origin, meaning they came from animals. The genetic material of these viruses is RNA. There are 7 types of coronaviruses (see picture) which are known to infect human and cause respiratory problem. Four of these are common coronaviruses (HCoV-NL63, HCoV-229E, HCoV-OC43 and HKU1) which causes common flu and the other three types have gone on to become epidemic worldwide- SARS-2002, MERS-2012 and Covid19. The 2002 strain is called SARS-Cov and 2019 strain is called SARS-Cov-2, and both these viruses have origin from bats. MERS had origin in bats too, and it’s spread was via  infected camels. If we look into their genomes, SARS-Cov and SARS-Cov-2 share 86% homology, sort of cousins.

pathogens-09-00231-g002
Animal origins of Human Coronaviruses

SARS 2002 caused death in about 9% of patients, with number of reported cases to be 8098 across 26 countries. MERS-CoV outbreak that originated in 2012 in Saudi Arabia spread to 27 countries with 2494 infections and 858 deaths, with a case fatality rate of 34.4%. Till now, Covid 19 has caused death in about 7% patients, with reported cases surging high and presently about 3.42M cases and 244K deaths in over 213 countries and territories. The major organ SARS-Cov-2 affects is lungs, but has potential to affect other organs like liver, intestine etc. Common symptoms are flu like fever, cough, headache cold etc. and in severe cases it causes pneumonia. The rate of transmission of Covid 19 really sets it apart from MERS 2012 or SARS 2002, thus making it a pandemic. MERS 2012 was a deadly disease, but its spread was limited as the illness spreads through close contact with people who already had an infection. SARS-2002 was deadly as well and affected upper and lower respiratory tract, it spread to over 26 countries, but transmission was contained by July 2003 after rigorous infection control practices which included isolating and quarantine. Covid 19 has spread all over the world in less than 3 months since the first reported cases in December 2019. It is airborne-virus, which makes the transmission fast. It is transmitted via air droplets when someone with virus coughs or sneezes. Sometimes, people might be carrying virus and not get any symptoms at all, but these people are able to transmit the virus and infect others. The incubation period, which is the time virus is spends in body before any symptoms are visible is about 5-7 days for SARS-Cov-2, which is longer than MERS and SARS. This incubation period also makes it difficult to identify if someone is sick. Alongwith this SARS- Cov-2 can stick to surfaces and remain on them for few hours, leading to transmission via contact with these surfaces. All these features added, make the transmission fast and difficult to contain the virus. Currently, the best solution we have to minimize transmission is that we avoid our contact with others and avoid going to places, this is called social distancing. For this reason, the countries have opted out drastic step of lockdown, so that we can stop the spread of this virus. We don’t have any cure yet for it and our medical services are not equipped to tackle such high number of cases at once. With lockdown, we are slowing the spread so that we don’t overwhelm our medical services and patients get treatment.

I will end this here and will discuss more on Covid19 in next blog. Remember the best way to combat Covid19 is by not spreading it, STAY HOME and STAY SAFE

Resources:

Photo by CDC

Javier A. James et al. Phylogenetic Analysis and Structural Modeling of SARS-CoV-2 Spike Protein Reveals an Evolutionary Distinct and Proteolytically Sensitive Activation Loop. Journal of Molecular Biology, 19 April 2020. Doi: 10.1016/j.jmb.2020.04.009

Firas A. Rabi et al. SARS-CoV-2 and Coronavirus Disease 2019: What We Know So Far.

Pathogens. Link : https://www.mdpi.com/2076-0817/9/3/231/htm

World Health Organization. Summary of probable SARS cases with onset of illness from 1 November 2002 to 31 July 2003. 2004.

 


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