The Biology of coRoNAvirus

The Biology of coRoNAvirus

Highlights

• What is CoV- CoronaVirus?
• What is SARS- Severe Acute Respiratory Syndrome (SARS)?
• What is COVID- COrona VIrus Disease?
• Which virus causes COVID-19?

CoV- CoronaVirus

All living organisms have DNA as their genetic material but biology is known for its confounding exceptions. And in this case the exceptions are viruses. Viruses can have RNA as their primary genetic material instead of DNA. At the moment, we are in the midst of a global pandemic caused by one such RNA virus “SARS-CoV-2”. The term “coronavirus” is all around us. Corona means “crown” in Latin. If you observe coronaviruses under a specialized microscope, you will see circular structures surrounded by spikes that resemble a crown, that’s how coronaviruses get their name.

SARS- Severe Acute Respiratory Syndrome (SARS)

Coronaviruses have co-existed with us for a really long time, at least 10,000 years. Then why is it that we are hearing about it only now? Well, if you think carefully, we have heard about it before too. The SARS outbreak in China in 2003, the MERS outbreak in Saudi Arabia in 2012 were all caused by these spiky coronaviruses. There are at least seven different types of coronaviruses that are known to infect humans. All of them cause upper respiratory tract infections. Coronaviruses HKU1, NL63, OC43, 229E commonly infect people around the world and cause one third of all common colds while SARS coronavirus, MERS coronavirus, and of course the one we are battling right now- SARS-CoV-2 cause more severe disease. 

COVID- COrona VIrus Disease

Why do we see a outbreak of a new coronavirus every now and then? Where are these new coronaviruses coming from? Coronaviruses are naturally present in bats, birds and a few other organisms which are called reservoirs- these organisms are tanks of active viruses but are not usually affected by the virus, which is pretty surprising and the subject of much of the ongoing research. In these reservoirs, viruses are constantly changing and evolving, at a rate much faster than humans or any other living organisms. In the process of evolution, there are times when the virus changes into a form that make them more efficient in infecting humans. If animals containing such viruses come into close contact with humans either due to habitat destruction or during animal trading/hunting, they are transmitted to humans through consumption of raw meat or as tiny air droplets and soon we have a local epidemic or worse, a global pandemic. In 2003, SARS-CoV made a jump from bats/civet cats to humans. In 2012, MERS-CoV made a jump from bats/camels to humans. And now we have SARS-Cov-2 which has probably jumped from bats/pangolins to humans.

We are all on the watch out for symptoms of coronavirus infection- dry cough, fever, breathlessness, diarrhea and fatigue. How does the virus affect the body in all these different ways? It all begins when we inhale the virus ant it enters our respiratory system. All coronaviruses predominantly infect lung cells. But why only lung cells and not any other cells in the body? This is because the spikes on the surface of the virus latch on to a specific protein called ACE2 which is present mostly on the surface of lung cells. One the virus latches and enters lung cells, it starts to do what it does best-multiply! The body tries its best to stop the virus by bringing in all the immune cells of the body to kill these infected cells and stop the virus from spreading. In the process, there is some damage to the lung cells making it harder to breathe. People with a proper immune system eventually clear the virus and repair the damage caused to the lungs while some others succumb to the virus. There could be several underlying genetic factors and health issues that make some people more vulnerable than the rest, something we need to study carefully.

How do we help our immune system fight these viruses?

One approach is to teach our body how to recognize the virus before getting infected, what we call a “vaccine”. Think of it as training a hound dog how to recognize a scent.  You inject certain unique parts of the virus such as the spikes on the surface of SARA-CoV-2 into the body and let the immune cells in the body generate antibodies to fight it. Now that the body already has spike antibodies, it can immediately recognize and kill the actual virus when the person is infected. Let us take for example, the flu vaccine. It is a weakened version of the flu virus that trains our immune system to recognize the actual flu virus. Sounds simple enough. Why can’t have a vaccine for every virus then? Because viruses are wily, evasive creatures. Every time they multiply, they are constantly changing and generating multiple versions of themselves which are all slightly different from each other. It is very hard to have one vaccine or one drug that can be effective against all different versions of the virus. That is why you have a different flu vaccine every season depending on the version of the virus that is currently in circulation. The key challenge is to identify something unique about the virus that doesn’t change very much with time and design a vaccine or drug based on that.

SARS-CoV-2

Talking about flu, did you know that both flu and SARS-CoV-2 are RNA viruses? So are Ebola, HIV, measles, dengue and many other viruses.  All of them use RNA as their genetic material. But the RNA sequences are different, the proteins they make are different, the cells that they infect are different, the way they cause disease is different, the way they are transmitted from person-to-person is different. The one thing they all do is to constantly change and make multiple versions of themselves challenging us to think of different ways to stop them.

The world as we know is constantly changing and we need to change too to keep abreast with these changes.