Over the past two years, viruses have received bad press. They have been typecast as evil and detrimental to our existence. On the other hand, we have projected ourselves as innocent victims of their ruthlessness.
We are led to believe viruses exist primarily to harm us. If we could, we would confer a heap of Nobel Prizes (Medicine, Economics, Chemistry and Peace) on anyone who accomplishes the total annihilation of viruses. This, however, would be a fatal error — far more lethal than any potential variant of Sars-CoV2 or even Ebola.
Barraged as we have been on the invasion of one virus and its mutant strains, it is easy to ignore that our planet hosts an estimated 10 nonillion (10 to the 31st power) viruses, enough to give one to every star in the universe 100 million times over. In comparison, there are less than 8 billion of us. We occupy microscopic space amidst them and they generally tolerate our presence until we start behaving like obnoxious guests.
Viruses have existed on Earth for 3.5 billion years prior to humans. They permeate every part of the natural world, lurking in soil, seawater, and drifting through the atmosphere. Almost all of them are harmless to humans, and many perform important functions in our ecosystem’s maintenance. Only 219 of the approximately 1.7 million viral species in mammals and birds infect humans. Others look after the health of specific organisms such as fungi, plants, insects, and even humans.
Bacteriophages, often known simply as phages, are viruses that infect and kill bacteria. In the ocean, phages are the most significant regulators of bacterial populations. They facilitate microbial creatures that produce half the oxygen in the world to survive in the ocean.
Phages are present in our digestive, respiratory, and reproductive tracts’ mucus membrane linings, and function as barriers against invading bacteria, thereby preventing infection and aiding our survival.
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Viruses that help and protect
For nearly a century, phages have been used to treat sepsis caused by lethal bacteria. These viruses were isolated from water bodies, dirt, air, sewage, and even from the bodily fluids of patients. Today, there is a renewed interest in using genetically engineered phages, especially in the treatment of drug resistant infections.
Viruses, such as the latent herpes virus and Pegivirus C, when present in our bodies, protect us from their harmful cousins. Antigens produced by the latent herpes virus assist the immune system in identifying and targeting cancer cells. Pegivirus C, often known as GBV-C, is a virus that does not cause any symptoms. Multiple studies have found that HIV and Ebola patients who are infected with GBV-C live longer than the ones who are not. By inhibiting the host receptors essential for cell entry, GBV-C slows disease and enhances the release of anti-viral interferons and cytokines.
Most significantly, viruses have played an integral role in the evolution of our species. We might never have existed but for them! Viruses have been infiltrating human genomes for hundreds of millions of years. Their genetic material accounts for roughly 8% of the human genome.
An artist paints a mural amid the Covid-19 pandemic in Assam. (Express Photo: Abhishek Saha)
Certain viral genes produce proteins such as Syntectin which enables the foetus to fuse with the mother through the placenta, but for which the embryo would die. Besides, retroviruses played a role in the evolution of the mammalian placenta. Researchers at Stanford believe that HERVK (human endogenous retrovirus K), which has been anchored in human DNA for over 200,000 years, protects the embryo against other viral infections.
Three hundred and eighty trillion viruses reside on and inside the human body, which is more than 10 times the number of bacteria. They infiltrate every part of the body including blood, cerebrospinal fluid, organs and skin. While a minority of them can be harmful to us, most of them coexist with us and many even facilitate our survival.
We ought to marvel at the ability of viruses to coexist with our cells, bacteria and other viruses in habitats as diverse as oceans and the human gastrointestinal tract. They prevent any particular microbe from becoming dominant, just as predatory animals keep prey populations in check. When populations become too dense, viruses replicate quickly and adjust the numbers, leaving room for all species to thrive.
When humans trigger viruses
Frequent contact between humans and animals usually by human intrusion into their habitats increases the risk of zoonotic viral transmission. Forest degradation for urban development, mineral extraction, hunting, slaughtering of animals, as well as worldwide animal trade have been important drivers of virus spillover.
A 2017 study published in the journal Science suggests that nearly half of the world’s species are already on the move as a result of rising temperatures and shifting rainfall patterns. According to the Lancet Countdown 2019 Report, climate change has facilitated the spread of many diseases, placing a rising number of people at risk. Growing populations, climatic change, and high rates of greenhouse gas (GHG) emissions are all expected to increase the number of Ebola-prone areas by 20% to 30%. Ebola could, on average, break out once every 10 years by 2070, dropping from the current average of 17 years.
When terrestrial animals migrate, they carry their viruses and transmit them. If humans invade their territories or cross their paths, new possibilities for pandemics emerge. If no action is taken to address climate change, about one billion people might be exposed to mosquito-borne diseases for the first time by 2080.
An outlook for the future
The Covid-19 pandemic is the result of the unfortunate but preventable confluence of ecological drivers of disease spillover. There is a reason why pandemics occur. The size of the host population and the degree to which it has disrupted the environment are major factors in the emergence of pandemics. Humans have significantly altered three-quarters of the Earth’s land and two-thirds of its oceans, according to the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES).
As wildlife shifts its distribution in response to human activity, disease spillovers will continue to occur across the planet. Two-thirds of human infectious diseases and three-quarters of newly emerging diseases are caused by animal spillovers. Wild mammals and birds have plenty of zoonotic viruses to transmit to us. We play a deadly game of viral roulette when we engage irresponsibly with other species.
Scientists have only recently begun to look at, and hence found ways, in which viruses maintain all life. As we stagger out of the pandemic, we must ensure safe and sustainable coexistence with other species. Ultimately, the more we learn about viruses, the more prepared we will be to use some of them for our good. We will also brace ourselves against those that could lead to the next pandemic.
We have emerged as the dominant species on Earth in the wake of the annihilation of other previously dominant species. It could be our turn to have the baton snatched from us. We have manipulated ecosystems for decades at peril to ourselves and to our planet. Ultimately, nature and viruses will decide how long all of us can coexist. Meanwhile, humility in recognizing our status as guests on our planet might be the best vaccine to safeguard our survival.
Rajesh M. Parikh is Director Medical Research and Hon. Neuropsychiatrist, Jaslok Hospital & Research Centre, Mumbai. He is Adj. Prof. of Psychiatry at the Carver School of Medicine, Iowa City, USA. He has authored two bestselling books on the Covid-19 pandemic and on vaccines in 2020 and in 2021
Testing for Covid-19 in Thane, Maharashtra. (Express Photo by Deepak Joshi) 
An artist paints a mural amid the Covid-19 pandemic in Assam. (Express Photo: Abhishek Saha)
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