Viruses are strange creatures. They are not even a complete cell that school textbooks describe as the basic unit of life. Viruses are a chemical compounds made up of only a handful of molecules.

These molecules arrange themselves in different orders to form various types of shapes. In the case of the novel coronavirus, these molecules make a sparkling red ball with crowns - giving identity to the family of coronavirus.

They are very, very small in size compared to their pathogenic cousins such as bacteria and fungi. They prey on almost any living organism. Some viruses infect other pathogens and make them sick. Bacteriophage is an excellent example. It infects and kills bacteria. Bacteriophage is considered as the reason why River Ganga water remained relatively bacteria-free before humans exceeded their capacity to keep the river water clean.

Coming back to viruses, they are so simple that most scientists don't even categorise them as living beings. Remember, school textbooks called them the link between the living and the non-living.

The novel coronavirus, scientifically named as SARS-CoV-2, is a comparatively large virus. Its size is about 120 nanometres - four times that of the poliovirus, which is just 30 nanometres. But a harmless Escherichia coli bacteria - the ones present in our gut - is some 16 times the size of the novel coronavirus. An average red blood cell in our body is about 64 times larger than the novel coronavirus.

The key molecule in all viruses including coronaviruses is protein. These are genetic materials and a storehouse of a very limited set of instructions - like a specific software programme. When these viruses get a favourable environment - namely, the body fluid - they start replicating themselves. This is their reproduction. They enter a cell and eat it from inside. When they leave the cell, they are in millions and the host cell is nothing more than garbage.

This is the way they wreak havoc among species including humans and crops. They are very smart and can travel through air, water, soil, droplets and from one person to other person. Through human-to-human transmission via saliva or mucous droplets, the novel coronavirus spread to all corners of the world after emerging from Wuhan in China. It took humans for a ride, literally.

Now, let's take a look at how the novel coronavirus behaves in our body. Proteins are crucial for the functioning of any living body. They don't only build muscles but they also establish the communication network within the body system. What is required, where and when, and how an issue inside the body is to be fixed is done by these proteins -- specifically, mRNA (messenger RNA), which perform the sentry's role in the body.

It is this variety of protein that keeps SARS-CoV-2 going. Typically, a human cell uses about 20,000 different types of proteins. Viruses use much less. For example, an HIV -- one that causes AIDS -- uses only 15 proteins to do its work. The novel coronavirus deploys 33, that too with the small size of its body.

Larger pathogens such as bacteria offer extra body space for medicines like antibiotics to block them from reproducing. The bacteria can be easily identified by antibiotics-induced antibodies as they flood outside the human cells. This behaviour makes them a suitable target for antibiotics/antibodies.

However, no antibiotic drug works on viruses because these germs don't reproduce on their own. They hijack the human host cell's physiology -- the miniature biological factory -- to make their Xerox copies. They leave one cell to invade millions others. They are always hidden. It is hard for medicine shots to kill viruses without damaging the body cells these pathogens have taken hostage.

There is another problem why treating viral diseases including Covid-19 is a bigger challenge. The viruses keep evolving almost continuously, but not significantly enough to be categorised as mutation. It is like changing clothes frequently.

This behaviour of virus confuses our immune system, whose responsibility is to detect the virus and neutralise the enemy. What happens often is that by the time the body's immune system detects the virus, the damage has already been done, and infection has transmitted to other person or persons.

Many a time, when body prepares for the fight with the invading virus -- the point when fever and other symptoms start showing up, the enemy is already on its way out after demolishing the fortresses of defence.

Doctors say the symptoms of fever etcetera are sometimes actually the response of the immune system rather than the virus. This is a stage where it may be too late for a patient. This is what is being seen in Covid-19 cases. A large number of Covid-19 patients died within 48 hours of their admission in a hospital. Those who were diagnosed earlier got well faster.

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How coronavirus behaves in body and why Covid-19 is difficult to treat - India Today