A warmer planet, sicker animals

Climate change will push many animals to flee their ecosystems for more livable grounds: By mixing more, species will also transmit more of their viruses, fueling the emergence of new diseases that may be transmissible to humans, a study predicts.

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“We provide evidence that the world will be not only warmer in the coming decades, but also sicker,” said Gregory Albery, a biologist at Georgetown University in Washington, co-author of the study published 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 charts an even darker trajectory for the planet’s future by 2070. And irreversible, even by limiting global warming to +2°C, the authors are concerned.

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

In total, 3139 species of mammals were considered – this class of animals is the one that harbors a great diversity of viruses that can be transmitted to humans.

More and more wild species are being driven from their natural habitat, which is deteriorating under the influence of rising temperatures, the decline of tropical forests, the advance of cities and cultivated areas, as well as traffic.

They then ’emigrate’ to new areas more favorable to their presence, where they have a greater chance of encountering hitherto unknown fauna.

With this geographical redistribution of ecosystems, more than 300,000 “first encounters” of species could take place, 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.

The study draws a future “web” of viruses jumping from species to species and getting bigger as the planet warms. It predicts at least 15,000 viral transmissions between species.

With bats playing a central role, these mammals are indeed the reservoir of many viruses, harboring them without developing the disease themselves, but able to infect humans through an animal host – “zoonoses” that are the origin of various epidemics such as SARS, COVID-19 or Ebola.

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

A more than worrying picture given that at least 10,000 viruses that can spread to humans are currently circulating “silently” among wild mammals, the study underlines.

How many will wake up and cross the human barrier? Will new families of viruses appear? The study doesn’t say so, but predicts the areas of the planet where fauna mixing will be concentrated: tropical Africa, Southeast Asia, in places where human populations will also be denser by 2070. Specifically, the Sahel, the Ethiopian Highlands and the 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 moving so fast that it is “bringing countless high-risk zoonoses on our doorstep,” warns Colin Carlson, also a co-author and researcher at Georgetown University.

Who compares the process to that of a ‘snow globe’ being shaken up? It is too late to reverse the trend, he said, but necessary “to recognize that global warming will be the main vector for the emergence of disease, and to prepare our health systems for it”.

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