Podcast. Why ecology and health are intimately linked
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Stagnant water – ideal for mosquitoes – and an epidemic of malaria develops. Cut forests, strong urbanization and it is bats, disturbed, which come to contaminate mammals. Environment, health and society are intimately linked. To understand how certain diseases develop and affect us, it can be helpful to take a step back and consider the world around us as a whole. That’s what we call ” the ecology of health”. How can the transformations of our environment and the evolution of our lifestyles have an impact on our health? How to learn to live with the living? Elements of answers in episode 1 of “The Knowledge Factory, Season 2”, a podcast from World produced in partnership with theEspace Mendès France in Poitiers.
At the microphone of journalist Joséfa Lopez, Serge Morand, biologist, health ecologist at CNRS, IRD and CIRAD and expert within the One Health program, Delphine Destoumieux-Garzon, research director and biologist at the CNRS, specialist in host-pathogen-environment interactions, and Patrick Mavingui, microbiologist and research director at the CNRS at the University of La Réunion, specialist in tropical diseases.
How to define “the ecology of health”?
Delphine Destoumieux-Garzon : It is the connection of different disciplines that makes it possible to make the link between human health, animal health and environmental health. This link provides systems-wide understanding of how species interact, how pathogens evolve, how they are transmitted, and what factors, both environmental and human, act on the whole system and lead to the appearance of diseases. ‘an epidemic. It is therefore a question of bringing together human medicine, animal medicine, the sciences of ecology and evolution. To put in place effective prevention approaches, it is also necessary to take an interest in agriculture, livestock, transport systems, etc.
Patrick Mavingui: The ecology of health makes it possible to see the systems involved in the emergence of diseases but also the emergence of the dynamics of transmission. This knowledge then makes it possible to stop or reduce the impact of diseases.
Concretely, what impact can human beings have on nature, which can then have consequences on their own health?
Serge Morand: The intensification of industrial livestock farming, for example, leads to the transformation of land use because it is necessary to feed more animals and therefore convert land and forests. This leads to a simplification of landscapes. Increasing urbanization also has its part. More than half of the human population lives in cities that continue to grow, especially in intertropical environments, in regions with high biodiversity. Result: we put together everything needed to promote the emergence and transmission of diseases.
PM: Ancient people understood the elements that can lead to the emergence of diseases. For example, for example, they did not do monoculture, rather polyculture, to prevent a single culture from being infected. Today, we have forgotten these basic principles which make it possible to avoid catastrophes. And then, the increase in world population inevitably leads to excessive occupation of land, in a more or less controlled way. Today, we are beginning to get closer to this ancient system because we cannot continue to destroy the environment, to get closer to the reservoir animals that live and co-evolve with these pathogens because this leads to the appearance of viruses in the being. human, such as SARS-CoV-2.
What types of diseases mainly affect human beings?
PM : If you study the age pyramid, you will find that man has evolved in these capacities to produce efficient and stable health. Technology now allows us to say that three quarters of the diseases that can infect humans are zoonoses, that is to say diseases of animal origin. And among these three quarters, we have a considerable part of them which are viruses, and RNA viruses. They therefore have a significant potential for mutation which generates variants, variants which allow them to pass from animals to humans and adapt to them. Now that we realize it, what is the answer? It is multiple: controlling our production on the one hand, protecting our environment on the other hand because the ecosystem is the place where these pathogens emerge. We must therefore try to find a balance between us, our animals and our ecosystem.
How to find this balance? Should we question our way of life?
D.D.-G. : We know that urban transport creates pollution, contamination and the transfer of pathogens. Food is also an important vector for the transfer of these pathogens. Going back to the local would, for example, reduce our impact on the environment and reduce the risk of spreading epidemics.
SM: We always think that we will find a technological answer to any problem, without trying to understand the ecological and evolutionary mechanisms. The resistance of bacteria to antibiotics is a good example. It clearly shows us that we are in an endless race. We will have to learn how to better manage our antibiotics rather than thinking that we will be saved by a new antibiotic. We are going to have to take into account the dynamics of living things and the dynamics of interactions between non-human living beings and humans.
How did we come to forget this link between environment and health?
D.D.-G. : We chose the easy way. This is true for intensive farming, it is also true for the use of drugs, etc. We have put in place these lifestyles without thinking about the consequences that this could have on the micro-organisms with which we live. They experience pressures on a daily basis and will then evolve in response to these pressures. At some point, chance means that the selection of such a germ, with such a resistance gene or such acquisition of virulence factors will cause it to become pathogenic for us.
Infectious agents also exist in the marine environment. How are they evolving?
D.D.-G. : I work on microorganisms that infect marine species, mainly marine invertebrates. We observe that they obey exactly the same laws as the micro-organisms that we know on earth. They experience the same pressures and evolve in the same way. Our human activity promotes their transfer on a planetary scale, in particular through international maritime trade. The environment − global changes, and first and foremost the warming of the oceans and the planet in general − will allow them to change their distribution areas. They are then found in new geographical areas.
What role does climate change play in the transmission of viruses and pathogens?
PM: I will take the example of Reunion Island, which I know well. There were initially sporadic transmissions of dengue by the tiger mosquito, with a relatively low number of cases. But since 2018, we have seen uninterrupted transmission of the disease. This continuity of transmission is due to the fact that the number of mosquitoes, which normally drops in the southern winter, no longer decreases as much because of the maintenance of temperatures. We have gone from an epidemic region to an endemic region of dengue transmission.
How to learn to live with viruses and bacteria?
SM : The health, ecological and climatic crises show that we must improve our resilience. The first resilience lies in our health systems, which have been very weakened, but also in animal health systems. It is necessary to invest, to maintain the quality of the services and to add to them an environmental health service which would be interested in the health of humans, animals and plants at the same time. We can manage the danger very well but separating humans from nature is nonsense. We must recreate this link between humans and nature, but with this scientific understanding of the phenomena. The proper functioning of ecosystems is the support of our civilizations.
Is interdisciplinarity important in the field of health ecology?
DD-G. : Yes, it is mandatory to move forward because the systems are very complex. Health ecology calls upon human and animal medicine, the sciences of ecology and evolution. If we really want to set up prevention approaches, we must also take an interest in agriculture, livestock farming, transport systems, etc. And as soon as researchers are trained, it is important that there have a common knowledge base. To take action, our politicians must also tackle these complex issues through interministerial actions.
A last message?
SM : Human beings must recognize that they are part of nature. He is a stakeholder, he lives from it. There are many more bacterial cells than human cells. We have genetic diversity. One is what is called an “extended phenotype”. This recognition must irrigate the implementation of new public policies. A positive message: we see that part of the administration is ready to collaborate, it just takes a little impetus.
D.D.-G. : You can only live well on a healthy planet. We are part of the system, we are not outside the system. I think the general public has understood that our health depends on the environment and the health of the species around us, whether plants or animals. This political awareness must be accompanied by ambitious measures. Our leaders need to help us a little more in this transition.
PM : At a time when information circulates enormously, let us trust science. Science questions and provides answers in a factual way. Rabelais said that “Science without conscience is but ruin of the soul”. Scientists know this. We must be wary of people who speak in the name of science without having the facts.
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“The Knowledge Factory” is a podcast written and hosted by Joséfa Lopez for The world. Directed by: Eyeshot. Graphic identity: Mélina Zerbib. Partnership: Sonia Jouneau, Victoire Bounine. Partner: Espace Mendès France in Poitiers.
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