To many people, the COVID-19 pandemic seemed to spring up out of nowhere. But ecologists and epidemiologists have been predicting a strikingly similar outbreak for years, revealing the deep-seated relationships between animal health, human health, and planetary health. 

COVID-19 is just one example of a zoonosis, a disease that was transmitted from animals to humans. Other examples of zoonoses include HIV, Ebola, SARS, and rabies.

According to the Center for Disease Control 3 out of 4 emerging infectious diseases in humans have animal origins. Additionally, a recent report released by the United Nations Environment Programme states that zoonoses are becoming increasingly common.

This is mainly because zoonoses “spillover” into human populations due to increased human-wildlife contact.

Human-wildlife contact is increasing for a few reasons, according to Dr. Kurt Sladky, a professor of zoological medicine at the University of Wisconsin-Madison and expert in ecosystem health. 

First, urbanization has caused human populations to spread into what was once wild, pristine habitat. This means that humans are coming into contact with wild animal populations that we have never encountered before.

Human consumption of wild animals for protein is another way in which zoonotic diseases can spread.

According to Sladky, bushmeat consumption is a key pathway in which zoonotic diseases spread to humans. Because of humans’ “voracious appetite” for hunting and eating wildlife, exposure to wild animals has been increasing.

Of course, some human populations, especially in the developing world, rely on consumption of bushmeat as their main source of protein. This makes these populations more vulnerable to contracting zoonotic diseases, Sladky said.

Deforestation is another way humans come into contact with wildlife harboring zoonotic diseases. The Ebola virus is a prime example of the ways in which deforestation allows zoonoses to escape their natural habitats and spread to human populations.

The Ebola virus existed in African rainforests, and cycled there between human populations, for centuries. However, since deforestation has become more widespread, the Ebola virus has expanded outside of these forests, and has caused 25 major outbreaks in countries across Africa, killing several thousand individuals. 

Unfortunately, experts say unless something is done to mend the damage inflicted on the planet and its natural ecosystems, future pandemics are expected to become more frequent.

“I only see these potential pandemics getting worse and worse because of what we as humans are doing to the environment,” Sladky said.

Additionally, Sladky noted how global travel via airplanes facilitates the global spread of disease. This has been documented during the COVID-19 pandemic, as well as other zoonotic disease pandemics and outbreaks. 

The COVID-19 pandemic should be a wake-up call to all of us that our actions are not just hurting the environment, but are actually hurting humans as well. 

Scientists call this the “One Health paradigm,” the idea that animal health, human health, and environmental health are all intrinsically connected.

Although each pandemic or disease outbreak has been previously treated as an isolated incident, it is crucial to remember that human actions are driving many of these events. 

In order to prepare ourselves for the future, understanding the connections between humans and our environment is critical in order to prevent future pandemics.