2023-04-23 10:42:48
What are they, how do they work. They are not harmful for everyone. On the contrary, many could be useful and it is good to know them
Nine times more than you thought. THE Rna viruswhich also includes i coronavirus like Sars-CoV-2, influenza viruses or those that cause colds, there are many, but now a study involving over one hundred researchers from all over the world, coordinated by Tel Aviv University in Israel, has shown that are many more than expected: samples of lake and ocean waters, soil and various other ecosystems have been identified over 100 thousand new unknown virusesa quantity that increases the mass of viruses known to date by nine times.
Without viruses, life would never have been born
The investigation took advantage of software capable of analyzing enormous quantities of genetic data and differentiating those coming from viruses from those of the organisms that host them, making it possible to reconstruct the evolutionary processes that have allowed RNA viruses to adapt to countless, very different, contexts environmental; It was also possible to understand how genetic exchanges allowed them to infect new organisms and thus propagate themselves in new situations. If at first glance this explosion might worry, it shouldn’t be like this, on the contrary: having discovered some that infect dangerous bacteria, for example, can pave the way for methods to control them precisely through viruses. Which are not always and only to be feared, far from it: the vast majority are not only harmlessbut even indispensable to our survival and that of other animals. And without the viruses on Earth life would never be born.
How many are there in the body
They cannot be considered living organisms in all respects, because they need to infect a host to be able to reproduce, but viruses are at the very origin of life on Earth: these tiny packets in which a DNA or RNA filament enclosed in a capsid, a small protein shell, have been among the earliest organisms able to exchange genetic material and thus allow evolution. Still they are the most abundant biological form on the planet and we shouldn’t fear them because they are literally part of us, as explained by the virologist and immunologist Luca Guidotti, deputy scientific director of the Irccs San Raffaele in Milan: All animals, including humans, are containers of microorganisms, true living chimeras. We have learned that in our body we host about thirty trillion bacteria (the microbiota, ed); well the viruses that live with us are 10 times more numerous. The human virome, i.e. the set of viral genes that we carry around, includes 300 trillion viruses, which colonize the bacteria and cells of all our organs, from the brain to the lungs, from the heart to the intestines. Not to mention all the viruses that pass through us because we introduce them with food: just think that in one gram of feces there are about a billion viral particles.
The misunderstanding in the name
The misunderstanding that makes viruses fearsome in our eyes arises from the very etymology of the word that identifies them, the Latin term for poison; of the approximately 300,000 different types of viruses estimated to infect mammals barely 1 percent is known and most of them are disease-causing species. All the others are useful or indispensable to our lives, but we know very little about them because it is difficult to identify them. Looking for them in the tissues is more complicated than sieving the soil and until about ten years ago the human virome was completely unknown; now slowly, thanks to metagenomics which studies genetic data on large populations, we are beginning to get to know some “good” viruses and to understand how they coexist with us, Guidotti observes. For example, we now know that phages, viruses that infect bacteria, are essential for keeping the intestinal flora in balance. Without phages to regulate the replication of intestinal bacteria, the microbiota would be “wild” and out of control.
The best and the worst
Studies on the intestinal virome are among the most advanced, because recovering viruses from feces is easier than going to look for them in biopsies of other tissues; so in the last year and a half it was discovered, for example, that there are viral species that are always present in healthy people, thanks to data from Danish Enteric Virome Catalog which is being built through the analysis of people aged 6 to 76 years. By comparing the data emerging from the project with the viromes being studied in other parts of the world, the research identified two viral genomes that are associated with a state of good health, a phage of the CrAss-like type and one called LoVEphage. Crass-like phages seem fundamental: research by Osaka University on the virome of almost 500 people with autoimmune diseases and about 300 healthy ones has revealed that Crass-like viruses are scarce in the intestines of those suffering from diseases such as rheumatoid arthritis or sclerosis multiple; in particular, viruses of the Podoviridae family that live in symbiosis with the Fecalibacteria appear to be deficient in the case of systemic lupus erythematosus, a chronic inflammatory autoimmune disease. According to the authors, characterizing the virome of autoimmune diseases could help keep them under control and something similar could also happen with inflammatory bowel diseases: a study by Massachusetts General Hospital of Boston showed that the virome of patients with ulcerative colitis or Crohn’s disease was abnormal. Viruses collected from the intestines of patients are capable of triggering an inflammatory response both in vitro and if they are implanted in healthy mice; on the contrary, transplanting viruses from the colon of healthy people onto animals protects them from intestinal inflammation.
Targeted therapies
Patients with inflammatory bowel disease may benefit from therapies aimed at eliminating the “bad” viruses, with vaccines or drugs, or with interventions that replace the abnormal virome with “good” viruses, for example with fecal transplantation of people’s viromes healthy, notes Kate Jeffrey, a gastroenterologist at the Harvard Medical School and coordinator of the investigation. There will come a day, therefore, in which, in addition to trying to encourage the proliferation of good intestinal flora, we will perhaps be able to enrich our body with good viruses: for now it is impossible because we know them even less than the microbiota, but they are the majority and, moreover, they have shaped a great deal in the course of evolution. As Guidotti specifies: 8% of our genome is made from retrovirus genetic materialwhich have “jumped” into our DNA and, for example, have given us the ability to develop the placenta: one of the essential components in the development path of this fundamental mammalian organ derives from viruses that we have incorporated into the genome in the past. The advantages given over the millions of years of evolution of life on Earth from viruses to bacteria and all other living organisms, including man, are many.
The purpose of viruses is symbiosis
As much as we may try to rehabilitate viruses, their bad reputation is deeply rooted and the word is enough to think of the many that are frightening: from those involving RNA, such as the hepatitis, HIV, or SARS viruses, to those in whose genetic material is double or single stranded DNA, such as herpes, chicken pox or smallpox viruses, the relatively few pathogenic viruses concern us. And yet, even they would not be bad per se, as explained by Luca Guidotti, deputy scientific director of the Irccs San Raffaele in Milan: Like any form of life, the purpose of viruses to survive and reproduce. To do this they need a host to give as little trouble as possible, the goal is to arrive at a symbiosis: at the apex of viral evolution there is the 99% we cohabit with, not those who harm us. It is no coincidence that highly pathogenic viruses cause epidemic outbreaks, but they do not spread that much and cause relatively few deaths; those that kill the most, as Guidotti points out, are intrinsically not very pathogenic, but induce chronic infections and reactions on the part of the immune system which then more or less quickly lead to death, such as hepatitis viruses or HIV. As if to say, they would not be bad but they become so through our response: a bit what happens with the cytokine storm believed to be the basis of many deaths from infection with Sars-CoV-2, which, explains the virologist. Not very pathogenic, it often infects without giving symptoms: this is why it could cause a pandemic. We are now witnessing the process of it becoming endemic, seeking a balance with our species. Even the speed with which it mutates and produces variants is not indicative of malice, but a normal process because with each replication there are errors and mutations which, however, at the population level, do not tend to select the meanest viruses, if anything, the opposite. It applies to all viruses, when they infect a new species: they may happen to be pathogenic, but not in their interest to kill usbut to evolve and change to preserve their “container”, concludes Guidotti.
ecological niches
For now, bird flu doesn’t seem to alarm us. But she should make us think. The virologist and immunologist of San Raffaele in Milan Luca Guidotti is not worried about the cases of avian flu reported this year, also because he says he is convinced that we would be ready to face an epidemic. Covid-19 has taught us a lot and we are more ready to create new vaccines in a short time. This, like other viruses that spread in intensive farming, should push us to change something in human behavior: infectious diseases become a problem when there are many susceptible specimens in confined spaces and with the population increase now we are the species that lives “in battery” such as chickens affected by flu, cattle or pigs. Today we are moving at speeds that were unthinkable a few decades ago and we have viruses that can spread everywhere in an instant, emerging from who knows where. Again, our fault: There are tens of thousands of viruses that we don’t know about and may be pathogenic, but most of them live in ecological niches where they would remain if we didn’t deforest and colonize the world: in 1930 60% of the land was wild, today less than 20%.
The HIV virus was in chimpanzees for thousands of years until we went to ‘disturb’ it, points out the expert. The leap of species that can occur when we invade ecological niches creates the conditions for epidemics and pandemics, which can then be more or less virulent depending on the population they find: Before Sars-CoV-2, a highly endemic coronavirus appeared 150 years ago , but then the average age was 50 and the deaths were much less, Guidotti points out. Trying to save ecosystems to prevent new dangerous viruses from emerging, it would also be advisable because antivirals are more difficult to make than antibiotics, as the virologist concludes: Bacteria have a different structure from our cells, hitting them without hurting us is easier. Viruses enter cells, the room for maneuver to hit them without harming us is narrower.
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April 23, 2023 (change April 23, 2023 | 10:42 am)
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