A warmer planet, sicker animals

published on Thursday, April 28, 2022 at 5:39 p.m.

Climate change will push many animals to flee their ecosystems for more livable lands: by mixing more, species will also transmit their viruses more, which will promote the emergence of new diseases potentially transmissible to humans, predicts a study.

“We provide evidence that in the decades to come, the world will not only be hotter, but also sicker,” said Gregory Albery, a biologist at Georgetown University in Washington, co-author of the published study. Thursday in Nature.

By cross-checking climate models, data on the destruction of natural habitats, and the way viruses pass from one species to another, this work draws an even darker trajectory for the future of the planet by 2070. And irreversible, even by limiting global warming to +2°C, worry the authors.

Their research – more than five years of work – has uncovered a mechanism where ecosystem disruption and disease transmission are intertwined for the first time.

A total of 3,139 species of mammals were taken into account – this class of animals being the one that harbors a great diversity of viruses capable of being transmitted to humans.

More and more wild species are driven out of their natural habitat, which is deteriorating under the effect of rising temperatures, the regression of tropical forests, the progression of cities and cultivated areas, as well as traffic. wild species.

They then “emigrate” to new territories more favorable to their presence. Where they are more likely to come across hitherto unknown wildlife, either indigenous or refugees too.

With this geographical redistribution of ecosystems, more than 300,000 “first encounters” of species could occur, ie double the current potential.

By mixing for the first time, these mammals will form new communities, fertile ground for new crosses of infections, especially viral ones.

– Bats as vectors –

The study draws a future “network” of viruses jumping from species to species, growing bigger as the planet heats up. It predicts at least 15,000 viral transmissions between species.

With a central role played by bats: these mammals are indeed the reservoir of many viruses, which they harbor without developing the disease themselves, but which can infect humans through an animal host – “zoonoses” at the origin of several epidemics such as Sras, Covid-19 or Ebola.

Winged, small, fast, they have a great potential to disperse across the planet and thereby infect a greater number of “naïve” species – encountered for the first time.

A more than worrying picture when we know that at least 10,000 viruses capable of spreading to humans are currently circulating “in silence” among wild mammals, underlines the study.

How many will wake up and cross the human barrier? Will new families of viruses appear? The study does not say so, but predicts the areas of the planet where the mixing of fauna will be concentrated: tropical Africa, Southeast Asia, in places where the human population will also be denser in 2070. Specifically the Sahel, Ethiopian Highlands and Rift Valley, India, Eastern China, Indonesia and the Philippines. Certain populations of central Europe would also be concerned.

But the threat is more global and climate change is so rapid that it “is creating countless risky zoonoses on our doorstep”, warns Colin Carlson, also co-author and researcher at Georgetown University.

Who compares the process to that of a “snow globe” being shaken. According to him, it is too late to reverse the trend, but necessary “to recognize that global warming will be the main vector for the emergence of diseases, and to prepare our health systems for it”.

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