The decline in biodiversity, which accelerates the emergence of viruses dangerous to human populations, increases the risks of pathogen transmission and the emergence of associated diseases, as sixteen heads of scientific bodies point out in an article published in Le Monde.
The current Covid-19 pandemic is a cruel reminder that human health, animal health and the health of ecosystems are closely linked, and that one cannot exist without the others, as emphasised by the interdisciplinary "One Health" approach, a fact that has been neglected for too long in both research priorities and public policy.
Coronaviruses belong to the huge Coronaviridae family, which circulates naturally in many animal species, with effects ranging from harmless to fatal. They are RNA [ribonucleic acid] viruses, which means they are highly susceptible to mutation, and have a very long genome, which means they are prone to recombination.
Four types of benign coronavirus are already known to affect the respiratory system in humans (they are thought to be responsible for 15 to 30 % of common colds) and, more rarely, the gastrointestinal, cardiac and nervous systems.
Three other types cause serious infections: SARS-CoV, known for having caused an epidemic of acute pneumonia in humans in 2002-2003, SARS-CoV2, closely related to the previous type and responsible for the current pandemic, and MERS-CoV, which struck in the Middle East in 2012.
Recombination between two different viruses
Genetic analyses show that SARS-CoV-2 belongs to the same Betacoronavirus group as the RaTG13 virus, isolated from a bat in China's Yunnan province. More recently, an even more closely related virus was isolated from the Malayan pangolin. The particular region of the virus protein that enables it to infect human cells is 99 % identical to SARS-Cov-2 (compared with only 77 % for the RaTG13 virus, which is unable to infect humans directly). This suggests that SARS-Cov-2 is the result of a recombination between two different viruses, one close to RaTG13 and the other closer to the pangolin virus.
The first lesson to be learned from this observation about the probable origins of the virus is that there would be no point in eradicating pangolins or bats. Viruses in this family are found throughout mammalian biodiversity, which includes many healthy carriers.
Since animals are largely involved in the emergence of new epidemics, it might be tempting to think that biodiversity represents a potential danger, since it harbours many pathogens. In reality, the opposite is true, as a wide diversity of potential or actual host species limits the transmission of viruses through a dilution effect. In addition, the genetic diversity of each species contributes to the emergence of host resistance to its pathogen, and therefore also limits transmission.
It is the decline in biodiversity which, by reducing host populations and thus the likelihood of the emergence of resistance, increases the risks of pathogen transmission and the emergence of associated diseases.
Numerous examples
A second lesson is that targeting human activities that directly impoverish biodiversity is a public health necessity. The pangolin is one of the most poached and threatened species, and this is particularly true of the Malayan pangolin, which is classified as critically endangered.
Its trade is strictly forbidden, yet more than twenty tonnes are seized each year worldwide, which suggests the scale of the total traffic. Meat consumption and the incorporation of their scales into traditional Asian medicine are the main reasons for this slaughter, and for the exponential increase in contact with humans. Bats, pangolins and humans have little reason to be in close proximity in the wild.
The only explanation for the switch from bats to pangolins, and then from pangolins to humans, is that they were hunted and brought together in a market. The Covid-19 pandemic is closely linked to the issue of the environment: once again, it is human disruption of the environment and the human-nature interface, often amplified by the globalisation of trade and lifestyles, that accelerates the emergence of viruses that are dangerous to human populations, through recombination between viruses of different species.
There are many examples, such as the hunting and poaching of wild (and even protected) species, which break the barrier of food safety (Ebola, SARS, Covid-19), or the destruction of habitats, which brings humans into close contact with endemic pathogens, such as Buruli ulcer in French Guiana, where the disease is increasingly affecting humans as a result of deforestation.
Evolutionary biology neglected
The export of contaminated bushmeat to densely populated regions (Ebola), and the intensification of passenger and goods transport across the globe against a backdrop of global warming, all encourage the spread of pathogens or pathogen vectors (dengue, zika, chikungunya) on a large geographical scale, as well as changes in their spatial distribution (malaria).
More than ever, the One Health concept must become a priority for interdisciplinary research, breaking down the barriers that still exist between the biomedical and environmental science worlds.
In the light of the current health crisis, it is paradoxical to note that evolutionary biology is still largely ignored in medical and pharmacy studies, and that it has recently become optional for two-thirds of a secondary school student's education.
Managing the current crisis, and better anticipating those that are bound to arise in the near future, means consolidating the foundations of a health ecology that looks at the interdependencies between the functioning of ecosystems, socio-cultural practices and the health of human, animal and plant populations taken together. Finally, it means drawing practical and political conclusions from the knowledge it provides, without waiting for the next crisis.
Signatories: Elsa Cortijo, Director of Fundamental Research at the French Atomic Energy and Alternative Energies Commission (CEA); Bruno David, President of the French National Museum of Natural History; Michel Eddi, President and CEO of the French Agricultural Research Centre for International Development (CIRAD); Mehdi Ghoreychi, Scientific Director of the Institut national de l'environnement industriel et des risques (Ineris); François Houllier, Chairman and CEO of the Institut français de recherche pour l'exploitation de la mer (Ifremer); Hélène Jacquot-Guimbal, President of the Université Gustave-Eiffel; Nathalie Lemaitre, Scientific Director of the Institut de Radioprotection et de Sûreté Nucléaire (IRSN); Philippe Mauguin, President and CEO of the Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement (Inrae); Jean-Paul Moatti, President of the AllEnvi alliance; Jean-Marc Ogier, President of the Université de La Rochelle; Michèle Rousseau, President of the Bureau de recherches géologiques et minières (BRGM); Virginie Schwartz, President and CEO of Météo France; Stéphanie Thiébault, Director of the Institut écologie & environnement (INEE-CNRS); Valérie Verdier, President and CEO of the Institut de recherche pour le développement (IRD).
The signatories are all members of the board or council of AllEnvi, the French national research alliance for the environment.