To date, it is estimated that at least 10,000 viruses are capable of infecting humans, but most of them spread silently among wild animals. Events of “zoonotic spillover”, such as the transmission of viruses from animals to humans and vice versa, such as Ebola or SARS-CoV-2, sometimes occur. These events are quite rare, but may not be permanent. As a result of global warming, the reduction of habitable areas for these animals, together with the destruction of natural environments associated with human activities, tends to move them closer to inhabited areas. Colin Carlson of Georgetown University in the US and his team of biologists indicate that this dynamic will accelerate the rise of infectious diseases in the world.
Current global warming contributes to rapid changes in ecosystems and pushes many animal species to shift their habitats to new environments. However, animals that move carry with them pathogens: viruses, parasites and other bacteria responsible for infectious diseases. These changes in geographic distribution lead to species that were not previously in contact, facilitating transmission between these microorganisms. Thus, the researchers predict that at least 15,000 new interspecies climate viral infections will occur by 2070, even in the best-case scenario, where global warming is limited to less than 2°C. This increase will be accompanied by a greater risk of zoonotic spillover.
To achieve these alarming results, biologists looked at 3,870 species of mammals and estimated their future geographic distribution under different global warming scenarios. “The method is very good, comments Serge Morand, ecologist at CNRS Based on viral sharing networks among currently communicating mammals, Colin Carlson and his colleagues hypothesize the potential for unprecedented sharing between newly introduced species. »
These new interactions will take place around the world, but are expected to be particularly concentrated in “biodiversity hotspots” – areas where species’ ranges are widest – located in areas densely populated by humans. Thus, regions at high risk of zoonotic spillover would be located mainly in tropical Africa and Southeast Asia. This last region is home to the greatest diversity of bats, which, according to biologists, will play a driving role in increasing virus transmission. Indeed, this winged mammal – the only one! – harbors the most transmissible pathogens in humans and is able to fly long distances. This unique dispersal ability allows them to move their habitat and thus share their diseases more easily than any other mammal species. The current Covid-19 pandemic is perhaps an example of this: according to one of the scenarios considered for its origin, SARS-CoV-2 was transmitted from bats to intermediate animals before infecting humans.
For Serge Morand, “this predictive modeling study is very interesting in terms of its results, which should take many new working hypotheses to test”. Other studies should therefore deepen and elaborate these hypotheses. “In the future, livestock and livestock, which are mainly involved in the loss of biodiversity and the risk of epidemics, should be taken into account,” the ecologist added.
Colin Carlson and his colleagues are concerned because the phenomenon they project over the next few decades is already underway. The global Covid-19 pandemic would be a prime example of this, in a world where global warming is already more than 1°C and where certain species’ habitats have changed. According to these researchers, current efforts to reduce greenhouse gas emissions are insufficient to prevent an increase in the risk of virus transmission between species (and this, even if the increase is limited to 2 ° C by the end of the century). Thus, their results show the need to establish viral surveillance and studies to monitor changes in the geographic distribution of the species. Especially in the tropics, where zoonoses are more common and warming is faster.
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