Why is COVID-19 disease so infectious?

Hey everyone!

I hope you all are safe and doing well. I needn't remind you of the big Corona scare we all are facing. As India prepares for UnLock 1.0, and with the rainy season around the corner, I feel like sharing a bit of what is certain of the biochemistry of the virus behind the COVID-19 disease. (I'm bored, tbh :P )

    We know Corona-viruses are a large family of viruses which may cause illness in animals or humans. In us humans, several corona-viruses are known to cause respiratory infections ranging from the common cold "sardi" to more severe diseases such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS). The most recently discovered corona-virus causes the corona-virus disease "COVID-19".

Transmission electron micrograph of SARS-CoV-2 virions

To be honest, this new virus and disease were unknown before the outbreak began in Wuhan, China, in December 2019. COVID-19 is now a pandemic affecting many countries globally.

COVID-19 is an acronym that stands for "Coronavirus Disease 2019". This infectious disease is spread by a virus now called SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2). 

People can catch COVID-19 from others who have the virus. This disease can spread from person to person by the small droplets from the nose or mouth, which are spread when a person with COVID-19 coughs or exhales. These droplets land on objects and surfaces around the person. Other people then catch COVID-19 by touching these surfaces or objects, and then touching their eyes, nose or mouth. People can also catch COVID-19 if they breathe in droplets from a person with COVID-19 who coughs out or exhales droplets.

But Abhi, what makes it so infectious?

As we know, all viruses are basically composed of genetic material and protein. A lipid envelope is also extremely common. However, these are not unique, or particularly notable features of SARS-CoV-2.

Now the way the SARS-CoV-2 virus gets into human cells starts with a specific protein in the spikes around the virus latching on to a specific protein (receptor) on the outside of a human cell.

I think the most notable thing about SARS-CoV-2, and the reason why it is so infectious and contagious, is how strongly it binds with the ACE2 receptor — more than 30-fold as strong as SARS!

(NOTE: ACE2 stands for "Angiotensin converting enzyme 2". This receptor is present on cells in human airway epithelia as well as lung parenchyma. Angiotensin II is the natural ligand for the ACE 2 receptor.)

Due to this strong binding, humans are susceptible to get infected by SARS-CoV-2 much more easily and in much higher severity as compared to infections caused by other viruses belonging to the corona-virus family.

Thanks for reading!

Take care. Stay safe. Practice all known precautions ardently and encourage others to do the same.

See you soon :)