Animals of all kinds locked up in a market, a confined city, an invisible enemy raging, the world soon to its knees… The beginning of the script for a disaster film that could have been called Of bats and menand which could unfortunately know, like the good old family sagas, endless sequels. Remember, on the eve of the transition to the year 2020, on December 31, 2019, China and the World Health Organization (WHO) revealed to the world what had been whispered to each other for several weeks: the existence of an epidemic of viral pneumonia of unknown origin. If, officially, 27 cases are then identified, the virus – which is not yet called Sars-CoV-2 – has begun its macabre race. Three years later, Covid-19 has claimed nearly 7 million lives and infected nearly 650 million people around the world. As COP15 Biodiversity began on Wednesday December 7 in Montreal, which should make it possible to adopt a new global framework to put an end to the loss of nature by 2030 and thus avoid a sixth mass extinction, the future of humanity has perhaps never been so dependent on the fate of our two-, four-, six- or eight-legged neighbours.
Because there exists on this Earth a paradox and a virtual certainty: wildlife is gradually disappearing in the face of the endless expansion of humans (it is estimated that a million animal and plant species are in danger of extinction, while 600 vertebrates have disappeared since the 16th century); despite this, animal-borne viruses seem to be spreading like wildfire. Hence this observation: if the Covid-19 is the first pandemic of the 21st century, it will probably not be the last.
Unfortunately, the news seems to prove us right. The beginning of this century was marked by several epidemics of emerging viruses linked to zoonoses. Above the Covid-19Sars, Mers, Ebola, bird flu, zika, monkey pox (recently renamed “Mpox”) or Marburg fever show that diseases transmitted to humans by animal species have multiplied in recent years. According to the World Organization for Animal Health, about 60% of emerging diseases are of zoonotic origin. In Africa alone, their number has increased by 63% in the last ten years, according to the WHO regional office. Worse, a “particular peak was reached in 2019 and 2020, when zoonotic pathogens represented approximately 50% of public health events”, continues the organization.
“The biggest carriers of a virus are the Airbus A380s”
How to explain such an explosion over the last twenty to thirty years? Since the dawn of time, nature has been teeming with viruses, bacteria and microbes of all kinds waiting for the first opportunity to infect humans and spread through them throughout the planet. Some allow us to live, and form the microbiota – all the microorganisms that live in us -, others, on the other hand, attack us. The living loves nothing more than to conquer the living. It remains to be seen which viral, microbial and parasitic species are likely to make us sick, or, in the worst case, kill us. It is thus estimated that 5,400 species of known mammals in the world harbor some 460,000 species of virus, the vast majority of which have yet to be described.
Our lifestyles responsible for the increase in zoonoses
Monkeypox virus seen under a microscope.
© / Cynthia S. Goldsmith/Centers for Disease Control and Prevention/AFP
If man has lived with these viruses for thousands of years, either by adapting or by developing vaccines, the evolution of our lifestyles has reshuffled the cards. At the turn of the 20th century, men intensified their travels. By going to the four corners of the world in just a few hours of flight, men have transported viruses that were previously confined to a given region. “The biggest vectors of a virus are the Airbus A380, abounds Hervé Fleury, professor emeritus of virology at the CNRS and the University of Bordeaux. Imagine someone infected with Ebola who takes the plane. In just a few hours , he is in a large western metropolis…” The consequence is immediate: the virus spreads more quickly and in an uncontrolled manner, as we have seen for Sars-CoV-2. By occupying increasingly large areas of the globe, humans also contribute to disrupting the ecosystem and encouraging the transmission of viruses.
Then, the intensification of factory farming increases the risk of the spread of pathogens between animals. Mad cow disease, for example, or bird flu spread more easily in an enclosed area with thousands of specimens stuck together than in an isolated pasture. The wildlife trade also increases human exposure to the microbes they may carry. According to two recent articles published in the journal Science at the end of July, the Covid-19 pandemic would certainly have started in the Wuhan market where wild animals were sold. Even if gray areas still exist on the escape of this disease, and no intermediate animal has yet been identified between the horseshoe bat and man, this proves the impact that can have the proximity to wild animals in very busy places, such as this market in Huanan.
Finally, deforestation increases the risk of contact between wildlife, domestic animals and human populations. When we deforest, we reduce biodiversity and, therefore, the animals that naturally regulate viruses disappear. Climate change is also pushing many animals to flee their ecosystems for more livable lands, warned a study published in the journal Nature. However, by mixing more, the species will transmit their viruses more, which will promote the emergence of new diseases potentially transmissible to humans. The study draws a future “network” of viruses jumping from species to species, and growing as the planet warms. This is for example the case of the Nipah virus. In 2004, people in Bangladesh became infected after consuming fresh date palm juice that had been contaminated with fruit bats. The latter had moved closer to the plantations to feed and compensate for the destruction of their natural habitat.
In Africa, a continent particularly affected by zoonoses, population growth is leading to rampant urbanization and encroachment on wildlife habitats. Road, rail, sea and air connections are improving, increasing the risk of epidemics spreading from remote areas to major urban areas, the WHO notes in a report. As for Covid-19, the virus spread all the more easily and quickly as it emerged in the megalopolis of Wuhan, populated by 11 million inhabitants, before overflowing and traveling by air. to the four corners of the globe.
What will the next pandemic look like?
Faced with this observation, one question remains: what form could the next pandemic take? If no crystal ball gives the slightest detail, scientists try to build a bundle of clues. And the number one suspect is well known: the flu. “The risk of an influenza epidemic with recombinant viruses is the greatest, warns Hervé Fleury. The main danger lies in migratory birds which carry a very wide variety of influenza surface antigens. centuries without suffering from it, but can transmit these influenza viruses to other animals, such as pigs, where the virus can recombine before contaminating humans”. Especially since these animals, by definition, carry these pathogens over great distances during their migration. “We already knew that we were at risk of an influenza epidemic. We had a coronavirus pandemic, but the first hypothesis can still occur”, he continues. Another risk concerns an avian flu, of the H5N1 type, which could give rise to a pandemic. “At the moment, it has no pandemic capacity, and human-to-human transmission is very low, but in the event of recombination, it could become very dangerous”, explains the virologist. The case of influenza A (H1N1) in 2009 is interesting in this regard. It is a recombination between human flu, that of birds and that of pigs. A mosaic chimera that has adapted to the ecosystem in which it evolved.
Another risk concerns arboviruses (transmitted by mosquitoes). “Epidemics of this type will develop in Western Europe under the impact of global warming, such as Zika or chikungunya”, warns Hervé Fleury, who also warns against the West Nile. This arbovirus is transmitted to humans by mosquitoes that have previously bitten migratory birds. “The United States experienced its first case in 1999. Today, no State is spared. It is now established in Europe, and in France in the Mediterranean basin. It can cause mild illness, but also meningitis “, underlines the virologist. In our country, the tiger mosquito, which can be a vector of viruses such as dengue, chikungunya or Zika, was implanted in 67 departments in 2021.
How to avoid a future health disaster? A major project, called “One Health” and whose first five-year action plan (2022-2026) was published in October, should in particular make it possible to promote the sustainable development of the planet. The goal is to build sustainable health and food systems, reduce global health threats and improve ecosystem management. France also launched in 2021 the international initiative “Prezode”, which aims to prevent the risks of zoonotic emergences and pandemics by strengthening cooperation with the most affected regions of the world.
Ahead of the opening of COP15 Biodiversity, the UN Secretary General, Antonio Guterres, hammered home in undiplomatic language: “With our boundless appetite for uncontrolled and unequal economic growth, humanity has become a weapon of mass extinction”. The warning could not be clearer: destroying the living is tantamount to destroying us, humans. It is high time to defend biodiversity, too often relegated to the background. Our future, as inhabitants of a planet in peril, depends on it.