10,000 types of viruses threaten humans as a result of climate change

At least 10,000 types of viruses can infect humans. We haven’t encountered most of them and so far we’ve only moved between wild animal species. However, this will change dramatically due to climate change, writes a team led by Colin Carlson and Gregory Albury of Georgetown University in Washington, DC, in the journal Nature.

Together with collaboration partners from the USA and South Africa, they use detailed simulations to predict that rapid environmental changes could cause up to 15,000 new transmissions of the virus between animal species by 2070. This would also be the case if global warming remained at two degrees.

The reason: Rising temperatures and the associated environmental changes are pushing more and more species into new habitats with other animal species never seen before. In doing so, the researchers wrote, “many animals will bring parasites and pathogens with them to new environments.” Geographical shifts, expected to reach 100 kilometers or more even in the best-case scenario, will facilitate virus exchange between animal species.

This in turn could facilitate the transmission of pathogens from wild animals to humans, known as zoonotic spread, and thus increase the risk of infectious diseases emerging from animals to humans spreading in the next 50 years. “This work provides indisputable evidence that the coming decades will not only be hotter, but also worse,” Alberi says.

Few large-scale studies have examined how climate change may affect viral trafficking and emerging diseases. Colin Carlson and colleagues now study how the geographic ranges of 3,870 species of higher mammals could change by 2070 in response to different climate scenarios around the world. They modeled warming from two degrees to more than four degrees.

Using the virus’s distribution pattern, they predicted possible jumps in viruses across species for a subset of 3,139 species of mammals. According to modeling, such events can occur in at least 4,000 instances over shorter distances and up to 15,000 times over longer distances. This does not mean that a new virus is transmitted every time. Instead, there will be frequent transmission between the same species or the same viruses, increasing the risk of falling into the trap of the new host.

New encounters between mammalian species are expected to occur anywhere in the world, the researchers wrote. However, this will be more or less reliably concentrated in tropical Africa and Southeast Asia, even across different degrees of warming and across different speeds of spread of different types of fauna: in areas with high population density, in biodiversity hotspots and – in search of Optimal temperatures – at higher altitudes. In mountainous regions, animals coming from different directions will meet for greater species diversity.

“We’re probably already in the midst of these changes that we’re not tracking, and they’re making the pandemic a problem for everyone,” Carlson says. In addition, according to the authors, it will not reduce the risk of fallout if global warming remains below 2 degrees.

The new virus transmissions will be attributed mainly to bats, which can harbor many viruses without getting sick, and can also, as flying animals, span the distances between species with small spreading radii. Bats are also one of the animals most likely to be the source of the SARS-Cov-2 virus. In the case of direct transmission between two mammalian species, the more closely related they are, the more likely the infection will be transmitted. Then the similarity between cell receptors and the immune system is greater.

The families or types of viruses most likely to spread to humans and the animal species that jump from them cannot be modeled individually due to the great complexity. “When you try to forecast the weather, you track clouds and not individual raindrops,” says Albri, describing the focus of the study.

There are also regions such as the Amazon Basin and a small part of the Central African Basin where researchers say there will be almost no new encounters between species that were not previously overlapping. These are places with a very homogeneous climate, the warming of which does not allow completely endemic animal species and many small animal species to escape in time.

However, if climate change is a driving force behind cross-species transmission of viruses, increasing the risk of infectious diseases passing to humans, the authors say targeted surveillance at future hotspots is critical to identifying emerging infectious diseases. “To do this, we also need a healthy infrastructure to protect both animals and humans,” Albury says.

The increased risk of spread “is also another reason to keep our focus on reducing greenhouse gas emissions, protecting rainforests and all the things we already know were important,” Carlson says. However, the risks of the virus’ jumps down can only be slowed at the most: “Because the main news is: that this is happening, it can no longer be prevented by even the best possible climate change scenarios,” his colleague Alberi warns.


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