The loss of biodiversity would be the main cause of infectious disease epidemics

According to a new study published in Nature, the loss of biodiversity is the main environmental cause of infectious disease epidemics, which become more dangerous and widespread.In what is called a 'meta-analysis' in technical jargon, the researchers found that of all the 'factors of global change', species loss was the most important in increasing the risk of epidemics.Climate change follows, chemical pollution and the introduction of non-native species.Urbanization was instead associated with a decrease in risk, this is because urban areas tend to host fewer wild animals and to have better sanitation infrastructures compared to rural environments.The experts they analyzed 2,938 observations of infectious disease responses to drivers of global change in 1,497 host-parasite combinations, covering every continent except Antarctica.

Interest in zoonoses, diseases caused by agents transmitted directly or indirectly from other animals to humans, has increased after the Covid19 pandemic.Regardless of the actual origin of Sars-Cov2, there are many pathologies that currently alarm global health authorities, such as swine flu and avian flu, which undoubtedly originated in wildlife.Overall, three quarters of emerging diseases in humans they are zoonotic.Previous studies have already highlighted the link between these pathologies and environmental changes, but it had not yet been clarified which factors had the greatest impact.The researchers also noted that many of the factors are interconnected.For example – the scientists wrote – “climate change and pollution cause the loss and fragmentation of habitats, which in turn can induce greater loss of biodiversity”.

The onset of new etiological agents, however, is not an event completely beyond our control, rather an event that almost always has its own potentially avoidable genesis.The requirement, however, is to be ready to change the impact of man and production on the environment.From the Mers virus which passed through dromedaries before arriving to us, to HIV which reached humans directly from its chimpanzee cousins:it is no coincidence that all potentially epidemic infectious diseases have developed in contexts in which spillover - the so-called 'species leap' - has been facilitated.The same goes for the Ebola outbreaks and the two coronaviruses that caused the SARS epidemic.A relationship published by the WWF, for example, highlighted already in 2020 that between the loss of biodiversity and the occurrence of epidemics there is a close connection and that, in particular, "the passage of pathogens from wild animals to humans is facilitated by the progressive destruction and alteration of ecosystems".Wild species, therefore, constantly threatened, are sacrificed in ever smaller areas where contact with human activities is increasingly greater.«In the absence of natural buffer zones – explained the document – ​​man is critically exposed to diseases that otherwise would tend to spread exclusively among animal species».

In short, it is nothing new that the risk of new epidemics is exacerbated by devastation of the natural environment.A study published on Nature Food shortly after the Covid pandemic, for example, he even managed to generate a map of the most vulnerable areas of China in this sense.For this purpose, the researchers analyzed approximately 30 million square kilometers of forest, agricultural and artificial cover, along with the density of livestock and human populations, the distribution of bat species and changes in land use in the regions from this last populated.The results highlighted that human-livestock-wildlife interactions in China can potentially give rise to hotspots increase the transmissivity of coronaviruses from animals to humans.Therefore, not only the destruction of ecosystems, but also farms must be considered as 'special surveillance'.In fact, it is above all when animals are kept in intensive conditions that they become hotbeds of zoonotic diseases, as already happened in 2003, 2009 and 2012 for avian and swine flu.This is net of other possibilities of diffusion, such as the experiments of "gain of function“, probably at the origin of the spread of Sars-Cov-2.

[by Simone Valeri]