Visiting Viruses

Are viruses good or bad? Should we really visit one? AWell, given the present times, the instant answer would be: viruses are bad and there is definitely no need to visit them. There is a reason why we are urgently following social distancing. The evidence? SARS-CoV-2, of course! We all know that this virus causes the novel coronavirus disease, wreaking havoc across the world since the end of 2019. It has turned our lives upside down because of its rapid infection spree. Not only COVID-19, but viruses also cause illnesses like Ebola, smallpox, influenza, SARS, MERS, and dengue. But, did you know that if it was not for some viruses, there would be no humans? They probably played a crucial role in human evolution. For the last few years, scientists around the world have been exploring these agents of change to unravel several mysteries associated with them.

- Apeksha Srivastava

A Debatable Origin

Virologists do not have a single answer to the question of the origin of viruses. There are three possibilities. According to the escape or progressive hypothesis, viruses originated from genetic material that “escaped” from cells. The reduction or regressive hypothesis states that viruses evolved from organisms that lost genetic material over time, keeping only genes required for parasitism. Both these hypotheses consider the existence of viruses after cells. Could viruses have evolved together with cells? Could they have originated before? The co-evolution or virus-first hypothesis talks about this possibility. However, to date, there has been no clear explanation about where did viruses come from.

A Puzzling Existence

Viruses are strange. Outside a living cell, they are not alive. But, they start reproduction the moment they enter a living cell. They synthesize new copies of themselves and exit the cell to infect other cells. They are obligate parasites, which cannot complete their life cycle without exploiting a suitable host.

A virus can get inside a living cell if its outer coat and the cell surface of the host are compatible with one another. It is similar to the lock-and-key mechanism. This is what makes the viruses species-specific. Some viruses are further restricted to limited cell types within the host because of the same reason.

Some viruses are further restricted to limited cell types within the host because of the same reason. Since viruses reproduce without growth, it gets difficult to classify their existence as living or non-living. This exception makes them unique!