They have bad press, there is no doubt: SARS, MARS, EVE (the Ebola virus) and in particular SARS-CoV-2, a pathogen that since the end of 2019 has turned the world upside down with over 7.3 million infections and over 418,000 deaths.
But trying to encompass the phenomenon of “replicons”, as they are also known in biology, in one word (virus) is like trying to describe the universe by pointing out a single star.
In fact, their diversity is as huge as our ignorance of them.
According to an article by Ignacio López-Goñi, lecturer in microbiology at the University of Navarra, if we counted only the viruses capable of infecting microbial populations, the number would be something like 10 to the power of 31 (10 followed by 31 zeros) which significantly exceeds the number of stars in the visible universe which is 10 to the power of 22 (10 followed by 22 zeros).
Of that truly gigantic number, we only learned the genome of about 2,000 viruses about five years ago, according to the National Center for Biotechnology Information database.
“Viruses have been around, probably, from the origin of life. They are part of the background noise that comes from our most distant ancestor and have always been an integral part of our vital dynamics,” says Valeria Souza, a researcher at the UNAM Institute of Ecology, who believes that their origins must go back 4 billion years to when life first appeared.
“We only have the genetic fingerprints and we have lost the initial signal, just as we lost the Big Bang signal; it happened too long ago and left no trace.”
Between life and non-life
Viruses are the simplest biological entity in existence. They oscillate between life and non-life.
They are a kind of genetic zombie made up of nothing more than DNA or RNA, covered by a capsid, a layer of proteins that does what an orange or avocado peel does to the flesh of the fruit: covering the genetic material to protect it; and a little bit of lipid (fat), nothing more.
But their simplicity is only superficial. For Antonio Lazcano Araujo, professor at the Faculty of Sciences and member of the National College, “simplicity is not synonymous with primitive, and I always like to use the example of Ikebana, Japanese floral art that is wonderful; it only has a few twigs, with a few flowers, and a few green leaves. It is very, very refined… It’s the same thing with viruses.”
The sophistication is found in their intracellular parasitic capacity. What this means is that, while their existence continues outside a cell, viruses are nothing more than inert particles.
But once they are inside a cell, everything changes. “They become a tremendous Trojan Horse which has the ability to take control of all the cellular machinery in order to replicate itself,” says Ana Lorena Gutiérrez Escolano, professor at the Department of Infecotomics and Molecular Pathogenesis at the Center for Research and Advanced Studies (CINVESTAV).
The human virome
Historically associated with pathologies, the word virus has its root in the Latin ‘veneno’. This idea means that they tend to get tarred with the same brush, but the vast majority could not only be innocuous but even beneficial to the environment and to our bodies.
According to “El viroma humano. Implicaciones en la salud y enfermedad” (The human virome: Implications for Health and Diseases) published in the Havana Journal of Medical Sciences, in our bodies there are 100 times more viruses than eukaryote cells, making up what is known as the human virome, i.e. the grouping of all viruses found in our body, including viruses that cause acute, persistent, and latent infections.
This ancient interactivity would have left its mark on at least 100,000 known viral fragments.
This figure represents 8% of our complete genome and that, according to Lazcano Araujo, plays a fundamental role in our existence.
“Animals like us, dogs, or whales, develop from an embryo that generates a placenta, which is a large cell with many nuclei that do not divide. That is exactly the same phenomenon that we see in retroviral infections. Pathologists, for example, were able to quickly recognize an HIV infection when they found cells in which the nucleus multiplied but the cell did not divide. The genes that determine the formation of the placenta in placental mammals, and the genes that prevent HIV-infected cells from dividing clearly come from a retrovirus,” says this specialist in early evolution and the origin of life.
Federico Kukso reminds us in Odorama (Taurus, 2019) that ancient Greek doctors believed epidemic fevers originated in air infected by lethal emanations or “miasmas”, an idea that would prevail for centuries. The first time a virus was accurately described (the Rabies virus) was only a little over 100 years ago, and it was thanks to Louis Pasteur. Since then our knowledge has advanced, but not as fast as we would like. Given the size of the field of study, scientific efforts are comparable to launching probes to explore the near universe.
Currently, the Joint Genome Institute in California, United States, is developing metagenomic analysis protocols and in recent years has managed to analyze 3,000 different samples, generating huge amounts of data and “a 17-fold increase in our knowledge of viruses,” according to López- Goñi.
Our knowledge of viruses is ever-changing, just like their ability to replicate and adapt to new environments and mutate and transmit between organisms. These are characteristics that make them successful organisms from an evolutionary perspective.
With reference to SARS-Cov-2, Lazcano Araujo points out that we should, “Think about it not from the human point of view, but from the point of view of the virus. It spreads easily, multiplies easily, infects, and kills a very small proportion of humans, and the result is that it will continue multiplying for a long time.”
It is a phenomenon that although dramatic still causes amazement from a scientific point of view. “They are wonderful biological entities,” says Gutiérrez Escolano. “Unfortunately, they cause these types of disease that claim many human lives […] [but] they have taught us a lot about our understanding of Molecular Biology. How? Because they look a lot like our cells. From a genetic point of view, by studying their very small genomes (one cell has 30,000 genes and some viruses have just 5 or 10 genes) we have begun to see them not only as entities, but also to learn a lot about our own molecular biology, that of our cells.”