Pandemic a reminder: All life is connected

Throughout history, infectious diseases originating in animals have crossed the species barrier to wreak havoc on humankind. Famous examples include Ebola from bats, HIV and malaria from chimpanzees and gorillas, and the bubonic plague from fleas on rodents.

However, the relationship between humankind and the natural world has fundamentally changed in the last several decades, heightening the risk of these dreaded “spillover” events. The mounting anthropogenic — human-caused — disruption of ecosystems, increased contact with wildlife and pressure on the climate together accelerate the pathway from animal infection to human pandemic.

In modern times, about 75 percent of emerging infectious diseases are zoonotic, meaning they originated in animals. Like SARS, which infected 8,098 people in 2003, COVID-19 is suspected to have passed from bats through another mammal before infecting humans. Chinese wet markets, where live animals such as ducks, ferrets and snakes are sold and slaughtered, have been implicated in the origination and amplification of both viruses. These creatures would not naturally come into contact with each other, but markets bring them from their ecological niches into crowded, unhygienic conditions where diseases can spread between species, and into their human captors.

Although China has received much attention, it is far from alone in facilitating spillover events, nor are wet markets the only risky environment. Domestic animals raised through global industrial farming operations — or “factory farms” — may be an even more serious cause for concern.

In the United States, it is estimated that 99 percent of animal products are produced in factory farms, which hold massive numbers of stressed and densely packed animals. These conditions are perfect incubators for diseases like pandemic influenza. When two different strains of virus infect the same cell, there is an opportunity for them to combine and create a completely new virus. The result is a pathogen that the human immune system has never seen before, with high pandemic potential. The 1918 Spanish Influenza originated in birds and infected an estimated one billion people, while the 2009 H1N1 pandemic came from pigs and infected around 60 million people.

In addition to incubating disease, factory farms are major contributors to land use changes and habitat loss, which bring humans into more frequent contact with our wilder neighbors. When animals lose their homes and food supply, they venture closer to human communities in search of these necessities, creating opportunities for the exchange of pathogens.

Animal agriculture is also a major driver of climate change through deforestation and greenhouse gas emissions. Climate change, in turn, promotes opportunities for spillover. As temperatures rise, many species begin migrating towards the poles in search of new homes, bringing them into contact with new species and communities. Mosquito-borne diseases such as dengue and zika virus are expected to become more common as mosquitoes expand their geographic range, and increased rainfall provides ideal breeding grounds. Lyme disease is also increasing in prevalence as ticks migrate north, a problem compounded by decreasing biodiversity.

To prevent the next pandemic, we must target the forces driving spillover events — and this requires more than controls on wildlife trade. Action on climate change, including reducing greenhouse gas emissions and improving forest conservation, is needed. To reduce our greenhouse gas emissions, we must transition to low-carbon energy sources such as wind and solar. Not only is this necessary for mitigating global warming and extreme weather events, it also improves air quality, protecting against severe outcomes from respiratory illnesses. Conservation also minimizes disruption to ecosystems and habitat loss. Sustainable agriculture practices can be achieved through reducing the demand for meat, and improving livestock living conditions. These changes would alleviate the crowding and unsanitary conditions that promote outbreaks.

It is important to remember that epidemics have plagued humans for centuries, and likely always will. However, unmitigated anthropogenic activities make these occurrences far more likely. Once a spillover has happened, our urbanized, globalized society fuels the spread of the disease. COVID-19 has made it apparent that investments in public health, health care capacity and outbreak preparedness are vital to mitigating the impact of novel pathogens when they do arise.

The natural world evolved in balance. It should not be surprising that when we upset this equilibrium, there will be consequences. The forces shaping spillover events are inextricably linked. Climate and land use changes, habitat loss, deforestation and animal agriculture are all related to one another and the well-being of life on earth. By understanding this relationship, we can learn to live in greater harmony with the natural world and prevent pandemics before they begin.