The emergence of the COVID-19 pandemic reveals fundamental insights into the structure of our planetary community; we have created a disease-friendly world.
As of Tuesday morning, May 12, the novel coronavirus (SARS-CoV-2) has infected over four million people in at least 187 countries. More than 285 thousand people have died. And while many countries and U.S. states have begun to reopen public life, it is decidedly clear that COVID-19 will not fade away in the immediate future. The coronavirus is still moving swiftly and silently to new people and communities, threatening to overwhelm medical facilities across the globe.
In response to the infection’s continued spread, we humans are forced to confront several new realities for our interconnected planet. One of those realities is a phenomenon called zoonosis.
A zoonosis is an infectious disease that can be transmitted from animals to humans. These infectious microbes jump from animals to humans with more regularity than one might otherwise suspect. The CDC reports that “3 out of every 4 new or emerging infectious diseases in people come from animals.” Each year, zoonotic diseases (also known as zoonoses) are responsible for an estimated 2.5 billion cases of illness and 2.7 million deaths worldwide.
The broad category of zoonotic disease includes many well-known human illnesses like HIV, West Nile virus, Ebola, Leptospirosis, and avian influenza.
Coronaviruses are zoonotic too. As the World Health Organization explains, “several coronaviruses are known to cause respiratory infections ranging from the common cold to more severe diseases such as Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS).”
The virulent evolutionary success of the COVID-19 coronavirus, which is the only lethal coronavirus to have ever gone global, can be attributed in part to the virus’ physical structure and in part to the structure of our globalized world.
Paying attention to the coronavirus outbreak, and to zoonotic diseases in general, is an invitation to think more deeply about the relationships between human communities, other animals, and the ecosystems that we share. It is of growing importance to ask fundamental questions about the nature of zoonosis: How are animal diseases leaping into human populations, and why?
Pathogens spillover from their animal reservoirs into humans for a variety of reasons. Deforestation, road-building, resource extraction, and land clearing bring humans into closer contact with wildlife. At the same time, intensification of animal farming practices and growing markets for wild and exotic animals carry new species, and their pathogens, into urban centers. International networks of travel and trade exacerbate the rates at which infectious germs are able to spread. Humans, animals, and their microbial companions are being mixed and moved around in unusual and unprecedented ways.
Zoonotic outbreaks have become increasingly common as the ecological footprints of human communities grow. “Pandemics are on the rise,” Peter Daszak of New York City’s EcoHealth Alliance warned in a February op-ed in the New York Times. “We need to contain the process that drives them, not just the individual diseases.” Systemic approaches to controlling zoonoses, including prevention efforts that target the causes of interspecies pathogen transfer, will be a critical next step in confronting the threat of novel infectious diseases.
If we could travel back to the moment of viral spillover, when the SARS-CoV-2 virus was transferred into a human host for the first time, it is highly probable that we would find ourselves in a so-called “wet market” in Wuhan, China. There, we would encounter a veritable jumble of animals—both living and dead—that includes chickens, fish, rats, bats, turtles, civet cats, and pangolins. This wet market arrangement, with its eclectic mix of animal species and their attendant microbes, provides an excellent stage for the cross-species transmission of bacteria and viruses.
Recent genetic evidence suggests that the SARS-CoV-2 virus originated in bats and was either transferred directly to humans or via an intermediate animal species. The identity of the potential intermediate species is up for debate, but a recent article in Nature suggests that pangolins are a “prime suspect.”
Pangolins, for those who are not familiar, are scaly, ant-eating mammals. Imported in vast numbers to Chinese markets for food and traditional medicine, they are considered the world’s most frequently trafficked mammal.
The evidence remains inconclusive as to whether pangolins were key players in the spillover of SARS-CoV-2 into the human population, but the case study of Wuhan’s wet markets and the role of pangolins in the international wildlife trade are illustrative of larger imbalances in the ecological relationships between humans and other species.
Across the globe, we are pushing deeper into undisturbed areas and moving species around at a historically unparalleled rate. The growing demand for food, and meat in particular, has also led to the development of epidemic-friendly industrial food systems which force animals into ultra-close proximity with each other and with humans.
Chinese wet markets can be seen as a symptom of a larger, planetary malady; human societies have developed extractive regimes of engagement with the natural world that destroy ecosystems and the lives of countless non-human animals.
It is important to note that the causes of zoonotic spillover are widely distributed—and on the rise—across most parts of the planet.
In the northeastern United States, for example, habitat fragmentation and deforestation have been shown to decrease mammal diversity and elevate populations of white-footed mice, the principal natural reservoir of Lyme disease in the region. Ticks in fragmented landscapes feed more frequently on white-footed mice, and are also more exposed to humans. One of the unintended consequences of destructive landscape modifications is an increase in Lyme disease exposure in humans.
AIDS, caused by the HIV virus, can be traced back to a spillover event from chimpanzees to humans at some point early in the 20th century. African hunters, upon cutting into the flesh of a freshly killed chimpanzee, are presumed to be the first humans exposed to a virus that would evolve, move through the global human population, and eventually kill 32 million people.
Industrial chicken farms, which force large quantities of chickens into high population densities, provide superb conditions for avian influenza to mutate and spread.
To notice the ubiquity of these ecologically unsettling practices might help to provide a pathway forward in response to the COVID-19 pandemic.
It is essential that the global community begins to collectively interrogate the causes of emerging infectious diseases that originate in other animals. Simple solutions might reveal themselves by turning the causal pathways of zoonosis on their head.
Could we prescribe conservation allotments and restoration projects in response to outbreaks of Lyme disease? Might we frame debates about industrial food production within discussions of global health? Could wildlife hunting and trade be slowed by investing in sustainable livelihoods where extractive ecological practices loom large?
One of the many lessons that our civilization can glean from the current COVID-19 pandemic is a fundamental truth about the relationship between humans and the natural world: human health and ecosystem health are inextricably linked.
Perhaps, when we are able to notice this connection, we can begin to devise more responsible ways of living and caring for the more-than-human community of life. ▩
Frankie Gerraty is a writer and biologist based in Santa Cruz, California.