By Frédéric Thomas, Research Director, CNRS
One Health is a concept that emerged in different organisations[1] in 2004. In essence, it recognizes the strong connections between human health, ecosystem health, and animal health. The importance of this concept is currently shown by the accelerated emergence or re-emergence of diseases over the last few decades. Before the 20th century, global pandemics occurred on average every 100 years. This frequency is currently accelerating: in the last 30 years, it is easy to see that COVID-19 is just the most recent example in a relatively long and daunting list of emerging or re-emerging diseases (e.g., Zika, Ebola, H5N1, H1N1). We are clearly within the era of emergence. Until now, our approach has always been the same: we wait for the epidemics or pandemics to occur and then we try to control them, often in crisis situations and with variable success.
But what is the origin of novel pathogens in human populations? It has now been scientifically demonstrated that 75% of novel diseases are zoonoses—that it to say, animal diseases that jump to human populations. Now that we are aware of this, the next obvious action is to understand the processes responsible for these transfers. Again, it has been scientifically established that the loss of biodiversity is strongly involved in these processes. But why is that? Ecosystems rely on fragile equilibria, and microbes are a key part of wildlife biodiversity. When humans alter the balance within ecosystems, they also alter microbe communities. This has two major consequences overall. First, it increases the frequency of infectious diseases among wildlife species, and second, it multiplies the transfers of these pathogens to human populations, either directly or indirectly through domestic animals. These novel pathogens can mutate and acquire the capacity to spread among humans. When this point is reached—given current globalisation—they have the potential to cause a pandemic.
What crucial anthropic factors need to be considered? According to recent syntheses, land-use change, agricultural explosion, and urbanisation are responsible for more than 30% of emerging disease events. Wildlife trade—both legal and illegal—is likely to increase disease emergence because it brings species together that usually do not interact, as least so closely, and this favours the transfer of pathogens among these species and humans. Climate change also has major consequences because it forces many species to flee their natural habitats and geographic distributions. As a consequence, many species that had never interacted will rapidly be doing so: it is estimated according to a recent publication in Nature (May 2022) that 15,000 novel transmissions could occur among species before 2070.
Despite the current bleak outlook, we can still escape the era of emergence. The solution is in our hands: we need to change our practices and our relationships with biodiversity and ecosystem management. These pandemics are part of a pattern of human effects on the planet.
We need a paradigm change; we need to accept that prevention is better than control. Prevention is not only early detection and surveillance, it is also the protection of biodiversity if we want to tackle the problem at its root. Biodiversity loss is the spark causing the forest fire—biodiversity provides what is called “a dilution effect”[2]. Recent quantifications have also demonstrated that, from a financial point of view, pandemic preventions would be 100 times less costly than control, in addition, of course, to saving human lives. However, biodiversity protection is complex because the immediate drivers of biodiversity loss often have an indirect causation, being the consequence of increasing human demography, economical activities, cultural habits, poverty, conflicts between humans, and so on. Thus, we need to create synergies between public health and environmental protection strategies.
For scientists, the first recommendations are to identify and better understand the risks. For instance, it is estimated that there are still 1.7 million unknown viruses in mammals and birds, including 800,000 potentially able to infect humans. When we better understand the risks, we can change our behaviours and routines to reduce these risks. Early detection and rapid responses are the next steps. Finally, we need multi-scale global surveillance since an emergence anywhere in the world has the potential to become a pandemic.
The One Health approach proposes a holistic view of health, and it does not only consider zoonotic and vector-borne diseases. It has been broadened with the inclusion of other fields, such as antimicrobial resistance, toxicology and ecotoxicology, health in urban environments, plant health, and, more recently, cancer. All of these topics are crucial for future health.
Thus, it is no longer enough to control epidemics and pandemics; it is crucial on many fronts to prevent them from occurring in the first place. If we do not adopt a preventive approach, epidemics and pandemics will be recurrent, maybe as frequently as every decade or even more frequent, and it is possible that viruses will emerge that are much more virulent than SARS-CoV 2. For this task, we need good scientists to improve our understanding of the drivers and mechanisms of disease emergence at different scales. We also need to encourage more connections between fundamental academic sciences and translational research to turn this knowledge into concrete strategies that are easily adaptable by local stakeholders around the world. Finally, given that pathogens do not stop at borders, international coordination and collaborations with interdisciplinary scopes are key to the success of preventing and controlling pandemics. The COVID 19 pandemic has revealed the current unsatisfactory integration of these issues.
Even though much work remains before us, we can still escape the era of emergence.
[1] the World Health Organization (WHO), the World Organisation for Animal Health (OIE), and the Food and Agriculture Organization of the United Nations (FAO).
[2] The "dilution effect" implies that where species vary in susceptibility to infection by a pathogen, higher diversity often leads to lower infection prevalence in hosts. For directly transmitted pathogens, non-host species may "dilute" infection directly and indirectly. The same occurs with vector-borne pathogens.
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