The link between climate and zoonotic diseases: myth and reality

In recent years, social media has been divided between two extreme narratives. One says: “Climate change will cause new pandemics.” The other: “The link between climate and viruses is a fabrication.” Both are wrong, but both are convincing in their own ways — one based on fear, the other on comfort. The reality, as always, lies somewhere in between and is much more interesting.

What is a zoonotic disease and why does climate matter?

A zoonotic disease is an infection that is transmitted from animals to humans. The causative agent can be a virus, bacteria, parasite, or fungus. Approximately 60 percent of known infectious diseases in humans are of zoonotic origin. Influenza, malaria, Ebola, Lyme disease, hantavirus, etc.

Climate change is an invisible but important player in the history of infectious diseases. It does not directly “create” viruses, but it changes the environment in which humans, animals, and pathogens encounter each other.

The first change is geographical.

Insects that spread diseases are temperature-dependent. Warm winters and longer growing seasons allow them to move into new areas. As a result, infections appear in regions where people have never encountered them before.

The second change is the expansion of border zones.

Deforestation, urbanization, and the expansion of agriculture are reducing the distance between humans and wildlife. The more often these two worlds intersect, the greater the chance that a pathogen can "jump" between species.

The third change is animals migrating. Climate change is changing animal migration routes. Species that were previously isolated from each other are now coming together in the same ecosystem—and viruses are moving with them.

So, is this a signal of a "new pandemic"?

No. And this distinction is important.

For a new virus to become a pandemic, several conditions must be met simultaneously: the pathogen must be new to humans, it must be able to replicate in the human body, and most importantly, it must be easily transmitted from person to person.

Climate change affects the first two conditions: it increases the likelihood that a person will come into contact with a new pathogen. But the third condition, human-to-human transmission, is an inherent biological property of the virus, which climate cannot directly determine.

In other words, climate change increases the likelihood of humans and a new pathogen coming into contact. This does not automatically mean a pandemic. It is simply that the background risk becomes higher, and it is this difference that is important.

"One Health" — a concept that is still not heard enough

The international scientific and health community is increasingly talking about the concept of "One Health" — an integrated view of human, animal, and environmental health. The idea is simple: these systems are not separate from each other. Human health depends on the health of the ecosystem, and vice versa.

This concept is important because it changes the question. "Will climate change cause a new pandemic?" is the wrong question. The right question is: "How do we manage a system in which climate, ecosystems, and human health are all integrated?"

In short, climate change does not automatically create new zoonotic pandemics, but it does change the environment in such a way that contact between humans and pathogens becomes more frequent. This is why this issue is neither the realm of apocalyptic fantasy nor a conspiracy theory. The problem is that we humans still imagine ourselves as systems separate from nature, while the boundaries between viruses, climate, and ecosystems are much less clear than we think.

Dali Kekelidze

Head and co-founder of the Georgian Academy of Young Researchers

Doctor of Public Health Master of International Health (BPharm, MSc, PhD)