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How viruses hijack your cells 

By DR. EDUARDO GONZALES

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Transmission electron micrograph of SARS-CoV-2 virus. Photo courtesy of US National Institute of Allergy and Infectious Disease

 

We used to feel a sense of relief when we have cough, runny nose, and fever and the doctor tells us all we have is a common cold that is due to a virus because we know that respiratory viruses cause only benign illnesses that subside spontaneously in a few days to a week or so even without treatment.

Things have, however, changed the last few years. SARS, MERS, and now Covid-19 have given respiratory viruses a sinister reputation and, “virus” has become a dreadful term. But what exactly is a virus and how does it make us sick?

Several hundred thousand types of viruses infect mammals but only several hundred infect humans. While they cause disease, experts do not even agree on whether viruses are living or non-living things. They are not made up of cells. They do not use or produce energy nor perform any metabolic process. Practically the only thing they have in common with living things is they can reproduce or replicate.

What viruses are made of

Viruses consist simply of a genome (strands of DNA or RNA that contain genes which code for the production of proteins) that is covered by a protein coat (capsid) to protect the genes. Some viruses including the one that causes Covid-19 (whose genome is made up of RNA only) also have an envelope that covers their capsid, which they use to enter a human cell. The envelope is made up of a fat-like substance that can be destroyed by soap—that is why washing with soap and water is very effective in deactivating the SARS-CoV-2 virus.

Viruses vary in shape and size, but all are so tiny they cannot be seen even with the use of an ordinary microscope. It would take 33,000 to 500,000 of them, laid end to end, to stretch over one centimeter.

How SARS-CoV-2 harm cells

A virus is a parasite. It can’t reproduce on its own. It has to enter a cell and use the cell’s machinery to be able to replicate.

In the case of the SARS-CoV-2 coronavirus, an infected person sheds countless viruses in respiratory droplets when he or she coughs, sneezes, or speaks, or simply exhales.

One sneeze contains numerous droplets and each droplet contains thousands of viruses. The viruses are inert outside the body and degrade in hours to days. But if they get into contact with another person’s nose, eyes, or mouth, they can enter that person’s body and given the chance to replicate.

The immune system of a newly infected person will take some time or days to recognize the SARS-CoV-2 virus as invaders—this is the case for all pathogens that enter the body for the first time. The viruses are thus given time to attach to (with the help of their envelopes) and enter body cells.

Inside the cells, the viruses, by using some of their proteins (polymerases) and raw materials in the cells’ cytoplasm, generate numerous copies of their genome (RNA), which instructs the cells’ compliant assembly lines to produce the proteins that the viruses need to build capsids. Thereafter, each fresh copy of the viral genome is packed into a capsid to form a new virus.

The newly formed virus then envelops themselves with a piece of the infected cells’ membranes and diffuses out of the cells. The infected cells, having produced numerous viruses, get exhausted and die. The new viruses, meanwhile, attach themselves to other cells where they further replicate. If the person’s immune system is unable to mount an effective counter-attack, most of the cells in many organs will soon get infected, and the organs will start to fail, the infected patient becomes seriously ill and could die.

In some Covid-19 patients, some organ damage is not caused by the disease

In some severe cases of Covid-19, the damage to the vital organs including the lungs is not caused exclusively by the viruses. It is partly or greatly brought about by the overwhelming reaction of the person’s immune system to the viruses.

The immune system is the human body’s army. It is made up of billions of cells that have access to numerous forms of weapons. Normally, when the human body encounters pathogens, the immune cells, attack the invaders in a very orderly, well-organized manner and with just enough force to eliminate the invader. But sometimes, as in some Covid-19 patients, the immune cells go berserk. They essentially transform into an unruly mob that destroys everything in their path including normal tissues, damaging vital organs in the process.


Source: Manila Bulletin (https://lifestyle.mb.com.ph/2020/05/11/how-viruses-hijack-your-cells/)

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