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Public Health Depends on a Healthy Planet

Zoonotic diseases like Covid-19 are a classic example of where ecosystems and human health intersect.

Steeve Jordan/AFP/Getty Images
Bats are trapped to be tested for viruses in 2018 in Gabon. Steeve Jordan/AFP/Getty Images

The butterfly effect is a thought experiment about how a small change in a system—a butterfly flapping its wings—can ripple through complex, interconnected systems, eventually cascading into larger events, like a tornado in Oklahoma. Despite having been popularized by the 1993 Jurassic Park movie, it’s not as far-fetched as it sounds.

While there’s uncertainty about how the novel coronavirus originally infected people, it might have started as viral spillover (transfer) from bats or other wild animals. One emerging hypothesis based on DNA evidence is that, because of natural habitat destruction, horseshoe bats in China were forced into cities. Under increased stress, the bats shed viruses that were picked up by people and perhaps other animals in an early infection cluster. Alarmingly, some 75 percent of emerging infectious diseases worldwide are exchanged between humans and wild animals. Think West Nile, Lyme, Ebola, Middle East respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), and Zika. The deadly Ebola outbreak has been linked to deforestation in Africa and to virus spillover from consumption of primates or bats that places hunters, consumers, and wildlife at risk.

The butterfly effect is a good way to think about our increasingly interconnected world—which we treat with insufficient care. Decades of explosive human population growth and an increasingly mobile population—an average of 12 million people traveled daily by plane in 2019—have put us in close contact, squeezed natural habitats, and forced wild animals to occupy cities or perish. According to a recent United Nations report, habitat destruction and climate change are the leading factors putting one million species on the brink of extinction. Many surviving, stressed animals carry high virus loads (bats, small mammals, birds, chimps), while urban-dwelling species like pigeons and starlings, which tend to displace them, have also exploded in numbers and carry additional diseases.

Humans’ insatiable desire to eat meat is also increasing spillover potential. Crowding livestock (pigs, chickens) at feeding operations was a factor in emerging infectious diseases such as the H1N1 swine flu outbreak of 2009 and the H5N1 bird flu of 1997. Poaching, overhunting, and consumption of wild animals as food or trade, combined with the loss of predators that keep host animals like mice and deer in check, accumulate risks. All of this will worsen as we heat up the planet, force more animals out of natural habitats, expand year-round mosquito and tick ranges, alter bird and bat migrations, and melt the permafrost that may be harboring soon-to-be-released infectious organisms.

Minimizing the risk of another pandemic or other such unforeseen consequence of all these changes first means doing everything possible to protect at-risk people, speed the development of new medicines and vaccines, and care for one another by coordinated advance planning. The One Health program of the Centers for Disease Control and Prevention offers promise as a multisectoral approach to zoonotic disease prevention. The program works from the local to the global level, “achieving optimal health outcomes that recognize the interconnection between people, animals, plants, and their shared environments.” It now needs to be linked to international sustainability efforts that reduce pressures on the planet’s life-giving ecosystems through culturally appropriate social, urban, and environmental policy. Veterinarians working with ecologists and medical doctors also need rapid-response capabilities to locate and quickly contain emerging infectious disease hot spots.

Overhunting, butchering, “wet markets” where animals are highly concentrated and stressed, and transport of wild species that have elevated risks of zoonotic disease transmission should be strictly curbed without blaming any particular culture or wild animal: Notably, the United States represents 20 percent of the market in wild species trade, including for the pet industry, so we are all in this together. And American habits have also been responsible for outbreaks: In 2003, a shipment of 800 small mammals from Ghana to Texas led to the first-ever outbreak of human monkeypox outside Africa, after they were housed near prairie dogs that were then sold as pets.

Conserving at least 30 to 50 percent of Earth’s fast-dwindling wild areas, in collaboration with indigenous peoples, can begin healing the planet. Unfortunately, many still view this kind of statement as unrealistic, even though such a conservation scheme would cost nations an estimated $100 billion annually compared to $7 trillion already spent on the Covid-19 pandemic. It would slow climate chaos by reducing the emissions from cutting down rain forests, which release most of the carbon stored for centuries in soils and foliage to the atmosphere. Importantly, one in four of today’s medicines originally came from tropical rain forests—climate control centers of the world—that are quickly being decimated. Taxol, a drug widely used to treat ovarian cancer, was derived from temperate rain forests in the Pacific Northwest. At its peak, Taxol was worth over $1 billion annually. Had we liquidated these forests, the drug may never have been developed and those lives never saved.

New cures to diseases will be found in the natural world and perhaps derived from the immunity of healthy bat populations that have coexisted in natural areas with various coronaviruses for millennia. But this can only happen if we care for each other and the planet in times of crisis. As we recover from this pandemic, it would be dangerous to lose sight of the climate and biodiversity emergencies that not just scientists but also religious leaders like Pope Francis and the Dalai Lama are increasingly warning us about.

The coronavirus pandemic is a distress signal coming to us from imperiled ecosystems and wildlife; it is not a one-off event. The heroism of medical staff and the ingenuity of scientists around the world who have identified the virus and are now working on cures are inspiring. Similar creativity and resolve will be needed to inoculate the planet from ecological collapse while honoring the diversity of people around the world. As the fiftieth anniversary of Earth Day approaches, the best gift we could give not just our planet but ourselves would be to start viewing strong environmental policy as preventive medicine.