At a time when the debate about the way in which Man threatens his own survival by disrespecting Nature is launched, and in a close connection to the emergence of viral infections, of which the current pandemic is an example, as a consequence of the growing deforestation, we wanted to deepen this problem that places Portugal among the countries of the European Union with "abrupt deforestation" since 2015.
After all, what is the impact of this reality on Men's Health and the Environment? Ricardo R. Santos, a biologist and researcher at the Laboratory of Environmental Health Behaviours of the Institute of Environmental Health and at the Bioethics Centre, both belonging to the Faculty of Medicine of the University of Lisbon, presents us with a relevant and essential view for understanding the reality in which we live, inviting knowledge and reflection on the place of Man and the place of viruses in Nature, this “house” that belongs to everyone and is for everyone.
Waiting for Godot (1952), by Samuel Beckett, is a tragicomedy in two acts. Anyone who knows it will remember the caption of the first act, which is, after all, also that of the second: “A road in the countryside. A tree. Dusk”. Here, then, is the scenario where the whole play will unfold. Space ("a country road") and time ("nightfall") are elements visually perceived by the scenic route. As for why ("waiting for Godot"), it will be the characters who will clarify it through the dialogic way. But, what does a tree do there? Vladimir informs. Godot warned them that they had to wait "at the foot of the tree". The tree then appears to us as a point of reference, that is, as a second spatiotemporal element that, subtly, gives the piece its tragic-comic dimension. In the second act, the road is the same, the dusk is the same, but the tree, despite being the same, is no longer the same. Once with bare branches, it appears in this act covered with leaves. Although condemned to immobility, due to its necessary rooting, and its magnanimous verticality, it has as its backdrop a road that symbolizes mobility and horizontality. The meaning here is clearly metaphysical, and refers, in a way, to the human condition, facing movement and inertia. The tragic time is thus made evident by the symbolic power of the tree: an immobile time marked by the birth of leaves. “And in just one night!”, Vladimir will say, somewhat puzzled.
The tree has always had this capacity to fascinate us and to induce the flowering of myths, symbols, ideas, theories, models, and governments. The trees of life and knowledge. Trees as natural memory and support for cultural memory. Trees as a model for classifying beings from Aristotle to Porphyry. Philological, genealogical and phylogenetic trees. Augustin Augier's amazing botanical tree. The tree of the origin of Charles Darwin's species. Although almost absent from philosophy, with the exception of Hegel, trees are present in poetry, painting and photography (what about Ansel Adams' magnificent photographic work?!). It seems, therefore, that the tree appears to us as an archetypal image. The cult of the tree came with the first Republic, and in fact, a little earlier still in the reign of King D. Carlos, the Tree Festivities were already getting some expression (the first happened in 1907, in Seixal, very close to the place where this text was written). The protection of trees then reached a civic but also pedagogical dimension that has extended to the present day, which manifests itself spontaneously in the face of announced tree-felling, particularly those that are part of our daily life or that have a secret meaning (the first kiss?) or whose growth accompanies us (family picnics on Sundays?) or simply because, inexplicably, we feel good at the foot of a tree, perhaps because, like Waiting for Godot, it serves as a point of reference for our own life. Also in medicine, we find analogical appeals to the trees’ typical arborescence, whether referring to cerebral vascularization or to the pulmonary tree. And what about Nicolas Andry’s orthopaedic treatise, published in 1741, whose subtitle was "the art of preventing and correcting body deformities in children", establishing, at some point, an analogy between the correction of a crooked leg of a child and the correction of the crooked trunk of a young tree. Yes, Paul Valéry was right. “The tree - what a beautiful theme!”
A tree is not just a tree
A tree is not just a tree. A forest is not just a cluster of trees. In a forest there is no disorder; at most, an order alien to our logic. A tree, given its leafiness, can dominate the landscape, but it constitutes, in itself, alive or dead, a support environment, a micro habitat for other lives essential to the balance of ecosystems, particularly at the level of the forest canopy, one of the strata that is most alive with life. Fungi, mosses, plants, rotifers, nematodes, micro crustaceans, insects, arachnids, birds, reptiles, mammals, of a thousand colours and a thousand shapes, find shelter, food, water, land, protection, a place of domination, socialization, or reproduction in the trees, or a house for life on which survival depends exclusively. It is not only the occupation of a large area of land that matters, but also the proximity between trees, as it physically expands this support environment, allowing tree species and animals to move through the forest without having to step on the ground, which is always so dangerous.
At the same time all this happens, the tree fulfils its nature. Exposed to the elements, it responds to them and adapts. Although rooted, it moves. Trees’ flowers and fruits, when they have them, are exuberantly displayed so that the species proliferate, using different strategies, some of them unimaginable in their sophistication. Furthermore, the trees communicate with each other, not only through chemical signals that spread through the air, but also through their roots, which, in cooperation with mycorrhizae, form a wide underground communication network, thus allowing the sharing of compounds and chemical elements (glucose, nitrogen, potassium, phosphorus) between trees, of the same species and of different species, as well as chemical signs of stress, denouncing approaching dangers. Trees breathe and sweat, sipping water and mineral salts from the soil and absorbing carbon dioxide molecules from the air. They let themselves be impregnated by the sun's rays, and do photosynthesis. Trees produce their sap, necessary for their survival. In the end, they release oxygen molecules, like someone who is constantly blowing a ring of soap bubbles. The phenomenon appears to us as the vision (anthropocentric, of course) of a perfect dance between opposites or, for the less romantic, a perfect machine for recycling molecules. We, humans, exhale carbon dioxide. Trees return the oxygen to us so that we can breathe in again. But we are not the only ones to have an oxygen-dependent metabolism, and the trees are not the only ones to convert carbon dioxide into oxygen. In fact, in approximate terms, for every two oxygen molecules, one comes from "land forests" and the other from "marine forests", the latter composed essentially of phytoplankton.
The nature of viruses and viruses in nature
Viruses have a bad reputation. And there are good reasons for that. After all, throughout history, they have been responsible, directly or indirectly, for the deaths of millions of people. When they appear in the news, they are presented as a kind of serial killers, immediately provoking a whole warlike language and a collective feeling of "fighting" against an invisible "enemy", using a battery of "weapons" (drugs). In this regard, the film Outbreak (1995), by Wolfgang Petersen, in which a virus similar to Ebola with the fictional name of Motaba, and whose host was a monkey from Zaire, started an outbreak in a small fictional city, Cedar Creek, located in California. However, what is interesting to note here is, on the one hand, the war scenario that settles around that city and, on the other, the type of solutions that are placed on the table: the rapid discovery of an antidote by scientists or the total elimination of that city, dropping on it a non-nuclear bomb that eliminates oxygen and incinerates everything, including the virus, within a radius of about 1.6 km. It is clear that this film reproduces, in a certain way, the stereotype of the "American way" of solving problems, but these stereotyped views have a strong adherence to the reality, or rather, to the beliefs of many peoples other than just the American, although, sometimes, these do not focus on the military, but rather on science.
In fact, in this regard, it is never too much to remember the warning made by the winner of the Nobel Prize for Medicine, French biologist François Jacob: “The coldness and objectivity that so often fail in scientists, are perhaps more useful than fever and subjectivity to discuss certain human issues. Because it is not the ideas of science that provoke passions. It is the passions that use science to support their cause.”
“Death to the virus”, a hoarse voice is heard shouting in the empty streets. And the scream is echoed as bodies fall, or confined lives become less bearable. After all, we are animals that depend on social networks, whether they are real or virtual. Despite a life increasingly lived at a distance, the imposition of social distance causes a reaction. It is not a social approach that is claimed, but the salvation of a certain idea of freedom. However, the virus does not die. It will never die. And the reason is simple. It was never alive. They are thus a kind of "objects" that carry genetic material inside. In addition, one of their main characteristics is the fact that they are not able to replicate themselves, that is, they need to infect living cells to do so. Hence they are also referred to as "genetic parasites". They misuse living cells to replicate themselves, without giving anything back. "It's in its genes," someone would say sitting at a café table. And quite rightly so. It's really in their genes. Infect as many living cells as possible to replicate as much as possible and then infect as many cells as possible, and so on. Infect to replicate. This is the logic of what viruses do, which they have always done. Infect to replicate and not infect to kill the host. The death of the host is always a setback for viruses, as it means losing their replication "machine". From an evolutionary point of view, this does not make sense. Hence, there are many species, in particular mammals, that end up functioning as reservoirs for a whole diversity of viruses (some of them with zoonotic potential), that is, they are infected, but they do not get sick. They do not get sick because they are, in a way, adapted to the viruses they host. As long as they remain there, there is no problem. The problem will arise when, under natural conditions, the virus leaps the species barrier and infects humans.
"Blood ... is still the best thing we have running in our veins," wrote Woddy Allen. In 2017, Mark Kowarsky et al. decided to analyse the DNA that circulated freely in the veins of humans and, to everyone's amazement, found hundreds of bacteria and viruses that, as part of the human microbiome, were unknown until then. In other words, the diversity of bacteria and viruses that colonize our bodies is much greater than we suspected. In fact, the ubiquity of viruses is another interesting feature. In addition to our bodies, they are abundantly present in all ecosystems, be them marine or terrestrial. Ann Gregory and a vast team sought to determine the diversity of marine viral DNA between the Arctic Ocean and Antarctica. The results were impressive, as they discovered more than 195 thousand viral populations, distributed in five ecological zones - Arctic (in all depths), epipelagic, mesopelagic and bathypelagic zones of temperate and tropical seas, and Antarctica (in all depths) -, exposing the Arctic as an important viral diversity hotspot.
In a single drop of sea water, we can count (patiently!) about 10 million viruses. Few are able to infect large marine animals (fish, whales, dolphins) or humans, since most are phages, that is, viruses that only infect bacteria. However, we are now beginning to better understand the crucial role that all these viruses play in marine ecosystems and food chains, but also in the way the ocean responds to climate change.
For example, it is known today that viruses are fundamental in the so-called «biological bomb» (process by which carbon dioxide is transformed into organic carbon via photosynthesis, until it is finally seized in the deep ocean, preventing it from escaping into the atmosphere). On knows that viruses eliminate 20% of the oceanic microbial biomass every day, releasing carbon and nutrients that later enter the food chain, and it is known that viral particles can have an important impact, not only on the evolutionary trajectories of microbial communities, through horizontal gene transfer, but also in increasing their resilience through metabolic reprogramming.
As in marine ecosystems, viruses are also abundant in terrestrial ecosystems. At the level of the soil, for example, its abundance varies between 2.2 x 103 viruses per gram of sand harvested in the desert of Saudi Arabia and 5.8 x 109 viruses per gram of soil harvested in eastern Virginia, in the United States of America. Similar to what happens in the seas and oceans, these viruses play a very important role in biogeochemical cycles, influencing the microbial community's ability to decompose organic matter or to convert organic phosphorus into forms that can be used by plants.
Now, if it is true that viruses infect all types of living cells, bacteria, animals and plants, if it is true that they are present in all ecosystems, if it is true that, during the infection process, some viruses capture genes of their hosts in order to gain an advantage in subsequent infections, it is also true that infected cells retain genetic material from these viruses which gives them evolutionary advantage. When the sequencing of the human genome was completed, the scientific community was somewhat amazed at the amount of DNA that apparently did not encode anything and had no function. They even got it a name: "Junk DNA". But not everything that seems is.
Today, using new sequencing techniques and technologies and comparative genomics, we know that it is precisely this "garbage" that not only distinguishes human DNA from chimpanzee DNA, but that distinguishes all genomes from all “higher” forms of life. In fact, when we compare the genomes of several mammals, we observe that non-coding sequences are precisely those that vary the most, but are also those that, paradoxically, are more conserved than coding sequences. For example, when comparing the chimpanzee genome with the human genome, a similarity of 98.5% was found. However, what was being compared was the coding regions. However, when comparing the Y chromosome of the two species, it was found that they are very different. Although this chromosome has few genes, the difference is mostly found in the repetitive DNA fragments, which colonized the chromosome by the action of reverse transcriptase, a retroviral replicating enzyme. In other words, what really made it possible to distinguish, in their evolutionary trajectories, the various species of mammals was, after all, the "garbage" that they were accumulating in their genome. The best studied case is, without a doubt, that of placental mammals.
The placenta appeared, it is estimated, about 130 million years ago. In terms of development, it is the first organ to be formed, as it will support the foetus throughout the gestation period. However, its formation, considered a critical point, implies the implantation of the embryo, which results from the action of a set of retroviral proteins that derive from retroviruses that ended up being integrated, through an endogenization process, in the mammalian genome. The syncytin-1 gene is derived from a retroviral gene (the env gene) that promotes cell-cell fusion and, in primates, has the function of developing a layer of multinucleated cells, called syncytiotrophoblast, allowing the embryo to be implanted in the endometrium.
However, several syncytin-like proteins have been discovered in almost all placental mammals. Functional studies have shown that the role of these proteins derived from endogenous retroviruses is not limited only to the mediation of cell-cell fusion, but also seems to play a role in suppressing maternal immunity, in protecting the foetus against exogenous viruses, and appears seems to act as regulatory elements. Yes, viruses have a bad reputation. But it was them, these "genetic parasites", that possibly made us human.
As we saw earlier, the forest is of fundamental importance, not only as a "recycling machine" for carbon dioxide, but also as a support for an unimaginable diversity of life or as a reservoir of unsuspected genetic diversity, among other equally fundamental functions, such as prevention of soil erosion or water regulation. Perhaps because these important and fundamental roles are not close or visible to us, or even taught or communicated, public disinterest in everything that goes on in the forest is frequent. After all, we want to continue to have paper, we want to continue to buy designer furniture made from the most expensive wood, we want to continue to eat our steaks and our soybeans, we want to continue to use palm oil for energy production, etc. Meanwhile, distracted by our daily hustle and bustle in Europe, deforestation and the loss of forest biomass has been growing at a worrying rate. Comparing the 2004-15 period and the 2016-18 period, the variation in the deforested area is concentrated mainly in southern Europe and the figures are significant. In Portugal alone, the loss was 56%. The causes are several: expansion of urban areas, intensive farming, mining, fires, etc. Population growth is an interesting point here. At the beginning of the 20th century, for example, people who lived in Rossio had gardens and country houses two or three kilometres away, for example around Rua do Salitre. The south bank of the Tagus River was made up mainly of stately farms (known as the “south bank” farms), dominated by a rural landscape. Today, the population has increased and the city has expanded, taking the category of metropolis, becoming part of what was, in the past, countryside. The countryside became part of the city and the city became part of the countryside. The phenomenon of organic eating practices of consumers living in the city is, in this respect, relevant, and shows how, in the city, sustainable production and consumption modes are now sought, either through organic markets or through social gardens. Let us return, however, to the forest and the dangers it contains.
In humans, about 75% of emerging infectious diseases have a zoonotic origin, that is, the infectious agent is transmitted from an animal to a human. This is the case with rabies, for example. This is the reason why our dogs and cats must be vaccinated with a rabies vaccine. However, the majority (71.8%) of these diseases originate from wild species. And if that is the case, then there is nothing better than going to meet them to try to know and understand the diversity and ecology of the potential zoonotic viruses, which live in wild animals that live mainly in forests, as well as the "drivers" for their emergence as a disease. All of this will make it possible to improve mitigation processes in future epidemics. It was precisely for this purpose that the Viroma Global Project emerged. To know more and better, to be more and better prepared. The truth is that it is estimated that there are about 1. 67 million viral species not yet described , of which it is estimated that between 631 thousand and 827 thousand have zoonotic potential. The scale is undoubtedly overwhelming, but the path must be followed.
The contact with these reservoirs of potential zoonotic viruses has been widely studied. In the past, exposure to non-human primates has given rise to the emergence of diseases such as Ebola haemorrhagic fever, AIDS or adult T-cell leukaemia. In rural areas, such as in Cameroon, whose populations, poor, depend on what they hunt in the forest (bushmeat), contact with blood and body fluids of wild animals is not limited to hunters, but also to the entire community, thus increasing the risk of infection. According to a study led by virologist Nathan Wolfeet al., the population of Central Africa is infected with the Simian Foamy Virus, an endemic retrovirus present in most primates in the Old World, precisely due to contact with these primates through hunting and eating wild animals.
Thus, both deforestation, hunting and consumption habits of wild animals that are reservoirs of potential zoonotic diseases, or the increase in population density, or the trafficking of wild animals to be kept as pets, are risks that can cause a new infectious disease may emerge, capable of overcoming the species barrier. In this sense, what happened with the new coronavirus (SARS-CoV-2) should not surprise anyone. In 2007, Vincent Cheng et al., in an article published in the journal Clinical Microbiology Reviews, were very clear in their conclusion, which is reproduced here in its original language so as not to lose its meaning: «The presence of a large reservoir of SARS- CoV-like viruses in horseshoe bats, together with the culture of eating exotic mammals in southern China, is a time bomb. The possibility of the emergence of SARS and other novel viruses from animals or laboratories and therefore the need for preparedness should not be ignored».
In addition, according to current United Nations projections for world population growth until 2100, Africa will increase its population by another 3 billion, to 4 billion, and Asia will increase by another 1 billion, to 5 billion. Africa and Asia, together, will represent about 80% of the world population! The anthropogenic pressure on the forest, the territory, in short, the different environments, will be brutal. Social and economic inequalities will become even more evident. And if, on the one hand, the increase in population density and the expansion of urban centres will provide more contact with wildlife, with all the risks that arise from it, on the other, the identification of those risks and the understanding of biodiversity and ecology of the pathogens that inhabit these “inhuman” landscapes will allow us to implement programmes for surveillance, prevention, adaptation, and mitigation in the face of future possible epidemics.
However, this essay ends by attenuating a certain tone that may perhaps be understood as fatalistic. Let's be clear. What we have ahead of us, therefore, is a demanding specification plus an intergenerational ethical challenge. And the future, or rather, the future to come, will depend a lot on what we are able to do, but it will depend even more on how much we are able to change. Attitudes, behaviours, and habits, at all levels. Individual, community, cultural and, above all, civilizational. The challenges are immense, but the future is open. I wish it has a tree as a point of reference.
Ricardo R. Santos.
Biologist and researcher
Laboratory of Environmental Health Behavior of the Institute of Environmental Health of Faculty of Medicine of the University of Lisbon.
Bioetics Centre of the Faculty of Medicine of the University of Lisbon.