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Animal migrations due to rising global temperatures will likely lead to thousands of new viral transmissions across species in the next 50 years, many of which pose a risk to human health, according to a modeling study.

In a scenario of 2°C of global warming, there would be more than 300,000 first encounters between species, leading to over 15,000 cross-species transmission events of at least one novel virus to a naive host by 2070, reported Colin Carlson, PhD, of Georgetown University in Washington, D.C., and colleagues.

The highest concentration of new infectious disease transmissions are likely to occur in high-elevation, species-rich environments in Africa and Asia, they noted in .

Novel virus-sharing experiences are predicted to predominantly be driven by bats, Carlson and colleagues found, which are likely to harbor viruses that can be spread to humans.

The authors said that these findings emphasize the global need for viral surveillance and assessment of species-level changes that result from climate change. This is especially true in tropical regions, which are home to the greatest number of infectious diseases that are transmittable from animals to humans.

"Because climate change is shaking our ecosystems to their core, the way that we understand viruses and their ecology will need to evolve," said co-author Gregory Albery, PhD, also of Georgetown University, in a press briefing. "We need to start preparing for things not just as they are, but as they will be."

"This is happening, it is not preventable even in the best-case climate change scenarios, and we need to put measures in place to build health infrastructure to protect animal and human populations," Albery added. "Ultimately, this work provides us with incontrovertible evidence that the coming decades will not only be hotter, but sicker."

As species migrate in the face of environmental change, many animals will bring their pathogens and parasites into regions for the first time, Carlson and colleagues wrote. This poses a threat to global health, as many epidemics and pandemics originate in wildlife, resulting in "spillover" events when these pathogens jump to human hosts. While some models have attempted to track viral transmission hotspots, few have predicted where the highest-risk areas will be in the context of global environmental change, they said.

The authors modeled both species migration patterns and global warming scenarios to predict how and where climate change might create opportunities for viral transmission, specifically tracking risks to human health. They only included mammals in their projections, as they have the most complete biodiversity data and downstream relevance to human health and zoonotic disease emergence.

The team built species distribution models for nearly 4,000 species of mammals, and predicted geographic shifts based on four different scenarios for climate and land use changes by 2070. The final analysis mapped migration patterns for 3,139 mammal species.

Carlson and colleagues acknowledged that the species distribution models are sensitive to subjective choices made by users, which could have influenced these findings. They also noted that this model ignored many factors that may impact migration, such as animal social behaviors.

The team emphasized that lowering greenhouse gas emissions will not reduce the likelihood of climate-driven infectious disease emergence. Even if mitigation efforts are successful and the globe remains under 2°C of warming, wildlife disease surveillance and improved public health infrastructure will be necessary to manage risk of future pandemics, they added.

"We have to acknowledge that climate change is going to be the biggest upstream driver of disease emergence," Carlson said. "We have to build health systems that are ready for that."

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