Here's why the world needs viruses to function
Viruses seem to exist only to wreak havoc on society and to make humanity suffer. They have claimed untold lives over the millennia, often destroying large chunks of the world's population - from the 1918 flu epidemic that killed 50 to 100 million people to some 200 million people who died of smallpox only in the 20th century. The current Covid-19 pandemic is just one of many ongoing and never-ending lethal virus attacks.
If they were given the choice of waving a wand magically and wiping out all the viruses, most people would probably take this opportunity, especially now. Yet it would be a deadly mistake - more deadly, in fact, than any virus could ever be.
"If all the viruses suddenly disappeared, the world would be a wonderful place for about a day and a half, and then we would all die - that's the result," says Tony Goldberg, epidemiologist at the University of Wisconsin-Madison. “All the essential things they do in the world far outweigh the bad things. "
The vast majority of viruses are not pathogenic to humans and many of them play an essential role in strengthening ecosystems. Others maintain the health of individual organisms - from fungi and plants to insects and humans. "We live in balance, in perfect balance," and viruses are part of it, says Susana Lopez Charretón, virologist at the National Autonomous University of Mexico. "I think we would have ended up virus free. "
Certain viruses maintain the health of fungi and plants (Credit: Getty Images)
Most people are unaware of the role that viruses play in supporting much of life on Earth, as we tend to focus only on those that cause problems for humanity. Almost all virologists study only pathogens; it was only recently that a few intrepid researchers began investigating the viruses that keep us and the planet alive, rather than killing us.
"It's a small school of scientists who try to provide a fair and balanced view of the world of viruses and show that there are things like good viruses," says Goldberg.
What scientists know for certain is that without viruses, life and the planet as we know them would cease to exist. And even if we wanted to, it would probably be impossible to wipe out all the viruses on Earth. But by imagining what the virus-free world would look like, we can better understand not only how integral they are to our survival, but also how much we still need to learn about them.
Without a virus, the planet as we know it would cease to exist (Credit: Getty Images)
For starters, researchers don't even know how many viruses exist. Thousands have been officially classified, but millions may be present. "We only discovered a small fraction because people didn't look like much," says Marilyn Roossinck, virus ecologist at Penn State University. "It's just a bias - science has always been about pathogens. "
Scientists also don't know what percentage of the total virus is problematic for humans. "If you looked at it digitally, it would be statistically close to zero," says Curtis Suttle, environmental virologist at the University of British Columbia. "Almost all viruses are not pathogenic for the things that interest us."
Key to ecosystems
What we do know is that phages, or the viruses that infect bacteria, are extremely important. Their name comes from phagein Greek, which means "devour" - and devour they do. "They are the main predators in the bacterial world," says Goldberg. “We would be in big trouble without them. "
Phages are the main regulator of bacterial populations in the ocean, and probably in all other ecosystems on the planet. If the viruses suddenly disappeared, some bacterial populations would likely explode; others may be overwhelmed and stop growing completely.
It would be particularly problematic in the ocean , where more than 90% of all living material, by weight, is microbial. These microbes produce about half of the planet's oxygen - a process activated by viruses .
In the ocean, 90% of all living material is microbial (Credit: Getty Images)
These viruses kill about 20% of all ocean microbes and about 50% of all ocean bacteria every day. By eliminating microbes, viruses ensure that oxygen-producing plankton have enough nutrients to undertake high rates of photosynthesis, ultimately supporting much of life on Earth. "If we don't have death, then we have no life, because life is completely dependent on recycling materials," says Suttle. “Viruses are so important in terms of recycling. "
Researchers studying insect pests have also discovered that viruses are essential for controlling populations of species. If a certain species becomes overcrowded, "a virus will pass and wipe them out," says Roossinck. "It's a very natural part of ecosystems." This process, called "killing the winner," is also common in many other species, including our own - as evidenced by pandemics. "When populations become very abundant, viruses tend to replicate very quickly and kill that population, creating space for everything else to live on," says Suttle. If the viruses suddenly disappeared, competitive species would likely thrive at the expense of others.
"We would quickly lose much of the planet's biodiversity," says Suttle. “We would have a few species that would take over and hunt everything else. "
Without viruses, experts say, we would lose much of the planet's biodiversity (Credit: Getty Images)
Some organisms also depend on viruses to survive or to give them an advantage in a competitive world. Scientists suspect, for example, that viruses play an important role in helping cows and other ruminants to convert the cellulose in the grass into sugars which can be metabolized and ultimately transformed into body mass and milk.
Researchers also believe that viruses are an integral part of maintaining healthy microbiomes in the bodies of humans and other animals. "These things are not well understood, but we are finding more and more examples of this close interaction of viruses which are a critical part of ecosystems, be it our human ecosystem or the environment," says Suttle.
Roossinck and his colleagues discovered concrete evidence to support this. In one study, they examined a fungus that colonizes a specific herb in Yellowstone National Park. They discovered that a virus that infects this fungus allows the grass to become tolerant of geothermal soil temperatures . "When all three are there - the virus, the fungi and the plants - then the plants can grow in very hot soil," says Roossinck. "The fungus alone does not. "
In Yellowstone National Park, a certain type of grass has increased heat tolerance due to a virus (Credit: Getty Images)
In another case study, Roossinck discovered that a virus transmitted by jalapeno seeds allows infected plants to deter aphids. "Aphids are more attracted to plants that don't have the virus, so it's definitely beneficial," says Roossinck.
She and her colleagues have discovered that plants and fungi generally transmit viruses from generation to generation. Although they have not yet identified the function of most of these viruses, they assume that the viruses must somehow help their hosts. "If not, why should plants cling to it?" Roossinck said. If all of these beneficial viruses were to disappear, the plants and other organisms that harbor them would likely become weaker or even die.
Protector for humans
Infection with certain mild viruses can even help keep certain pathogens at bay.
GB C virus, a common human blood born virus that is a non-pathogenic distant relative of West Nile virus and dengue fever, is linked to delayed progression of AIDS in people with HIV. Scientists have also discovered that GB C virus seems to make people infected with Ebola less likely to die .
Likewise, herpes makes mice less susceptible to certain bacterial infections , including bubonic plague and listeria (a common type of food poisoning). Infecting people with herpesvirus, bubonic plague and listeria to replicate the mouse experience would be unethical, but the study's authors suspect that their findings in rodents likely apply to humans.
Herpes makes mice - and most likely humans - less susceptible to certain bacterial infections (Credit: Science Photo Library)
While lifelong herpesvirus infection "is generally considered to be pathogenic only," they write, their data suggests that herpes in fact enters into a "symbiotic relationship" with its host, providing it with immune benefits. Without viruses, we and many other species would be more likely to succumb to other diseases.
Viruses are also among the most promising therapeutic agents for the treatment of certain diseases. Phage therapy, which has been the subject of considerable research in the Soviet Union since the 1920s, uses viruses to target bacterial infections. It is now a rapidly growing area - not only because of the increase in antibiotic resistance, but also because of the ability to refine treatments to eliminate specific bacterial species rather than indiscriminately wiping it out. all of our bacterial populations, as do antibiotics. (Learn more about what we do and don't know about our microbiome ).
"Many lives have been saved by using viruses when antibiotics have failed," says Suttle. Oncolytic viruses , or those that selectively infect and destroy cancer cells, are also increasingly being explored as a less toxic and more effective cancer treatment. Whether they target harmful bacteria or cancer cells, therapeutic viruses act "like tiny microscopic guided missiles that enter cells we don't want," says Goldberg. "We need viruses for a continuation of research and technological development efforts that will lead us to the next generation of therapeutic products."
The disappearance of viruses would have an impact on the evolutionary potential of all life on the planet - including Homo sapiens
Because they constantly replicate and mutate, viruses also hold a huge reservoir of genetic innovation that other organizations can integrate. Viruses replicate by inserting themselves into host cells and bypassing their replication tools. If this happens in a germ cell (eggs and sperm), the viral code can be passed on to the next generation and become permanently integrated. "All organisms that can be infected with viruses have the ability to suck in viral genes and use them to their advantage," says Goldberg. "The insertion of new DNA into the genomes is a major mode of evolution." In other words, the disappearance of viruses would have an impact on the evolutionary potential of all life on the planet - including Homo sapiens.
Viral elements make up about 8% of the human genome, and mammalian genomes in general are dotted with about 100 remnants of genes from viruses. Viral code often manifests as inert pieces of DNA, but it sometimes confers new and useful, if not essential, functions. In 000, for example, two research teams independently made a fascinating discovery. A gene of viral origin codes for a protein that plays a key role in forming long-term memory by moving information between cells in the nervous system.
Ancient retroviruses are responsible for the human ability to have live births (Credit: Getty Images)
The most striking example, however, concerns the evolution of the mammalian placenta and the timing of gene expression during human pregnancy. The evidence indicates that we owe our ability to have live births to a little genetic code that was co-opted from ancient retroviruses that infected our ancestors more than 130 million years ago. As the authors of this 2018 discovery wrote in PLOS Biology: "It is tempting to speculate that human pregnancy would be very different - perhaps even nonexistent - without eons of retroviral pandemics affecting our evolutionary ancestors.
Experts believe that these signatures occur in all forms of multicellular life. "There are probably many functions that remain unknown," says Suttle.
Scientists are just beginning to find out how viruses help sustain life because they are just starting to search. Ultimately, however, the more we learn about all viruses, not just pathogens, the better equipped we will be to control certain viruses for good and develop defenses against others that could lead to the next pandemic.
More than that, learning more about the richness of viral diversity will help us open up a deeper understanding of how our planet, our ecosystems and our bodies work. As Suttle says, "We have to invest efforts to try to understand what exists, just for our own good."
This article appeared first on: https://www.bbc.com/future/article/20200617-what-if-all-viruses-disappeared