How well do we know viruses?

Every new virus that surfaces puts the scientific fraternity on red alert, for viruses have a notorious reputation for posing unprecedented challenges. Some (such as Ebola) are lethal with a high mortality rate, whereas others (like the coronavirus) transmit rapidly.

It is barely a century ago that we detected viruses, although they have been ravaging humanity for ages. It was only in 1901 that James Caroll and Walter Reed established that a virus was causing deadly yellow fever. Although they did not see the virus per se, they proved that the unknown, yet filterable pathogen, was smaller than the bacteria.

Viruses remained elusive to the eye until the advent of the electron microscope in the 1930s. It took another fifty years to see their structural details. Today, technology advancements provide us with greater clarity of their diversity. However, several aspects of their molecular functioning still remain to be understood.

Viruses are a class apart, neither living nor non-living entities, nor belonging to bacteria, plants or animals. Though they contain the primary life-juice – nucleic acid, they need a living cell to multiply, making them parasites. Viruses infect plants, animals and even bacteria, usurping the host cell machinery to replicate rapidly.

They are only a fraction of the 1400 or more species of pathogens that infect humans, and 250 known species exist. Studies indicate that in the past few decades, a majority of newly discovered infections have been due to viruses as each year three to four new species add to the list. There is yet a fair amount of unknown species.

Viruses are self-assembled nanoparticles of a core of genetic material (either RNA or DNA, but not both), lipids, and proteins to cover the centre and invade host cells. Once inside a living cell, they hijack the manufacturing unit – ribosomes, using it to produce the viral protein patterns. At the molecular level, the ribosomes know how to follow instructions without the ability to differentiate the source. Another cell component – Golgi complex does the packaging. Soon, the cell detects the runaway production, shuts down by self-destruction to prevent further damage. The cell wall bursts open to get rid of the viral particles. However, this works to the virus’ advantage as they get released in the vicinity, invading more cells.

Each viral strain uses different tactics to invade cells. Gaining insights into the molecular changes that occur is active, ongoing research. One such effort on the new coronavirus, a team of researchers at IIT Kanpur is attempting to view the structural transformations in real-time mode. Using highly advanced imaging instruments, they hope to see how the virus fights our immune cells, docks with the human cell and opens a pore in the cell membrane to transfer its genetic material. Their study may offer clues to develop a vaccine for Covid-19.

What makes viruses so dreaded is their mutations. The RNA-type viruses (such as the new coronavirus) tend to mutate more than the DNA type because their genetic material lacks a supervising code. Unsupervised production leads to mistakes, which result in different protein structures from the original copy. The changes dramatically influence the type of cells to invade.

Viruses are positioned at the lowest rung of the evolutionary ladder and hence under the constant pressure of survival. So, the mutated virus has a primary motto to look for a matching pattern in a living cell, latch on, propagate and thrive.

Experts caution that in the past few decades, species crossover of viruses is on the rise due to increased human-animal interaction. Almost 80% of the known viruses are found to perpetuate in animals — farm as well as wild. As we share several molecular commonalities with animals, we are highly susceptible to viral mutations that cross over.

Besides, extensive travel is causing endemic viral species to cross borders. A unified global code of immediate reporting of new viral strains, strict surveillance and containment measures is the need of the hour.

(The writer is a science communicator)