Spreading around the world at the speed of light, COVID-19 has now infected more than 2.5 million people and killed almost 177,000. Although the virus’s origins are still a little murky, it’s highly likely that it jumped from species to species, until it hit ours.
Trading diseases with wildlife isn’t new. In the Middle Ages, the bubonic plague—caused by a bacterium—originated in city rats and was typically transferred to humans via a bite by an infected flea. The 1918 influenza pandemic (Spanish flu) has been traced back to birds and killed an estimated 50 million people, about one-third of the planet’s population. In 2009, the less fatal swine flu was sourced to pigs raised for food in North America; and HIV/AIDS started as a virus in Old World monkeys in Africa. Recently, the frequency of disease outbreaks has been increasing steadily. Between 1980 and 2013, there were 12,012 recorded outbreaks, comprising 44 million individual cases and affecting every country in the world.
While many bacterial, fungal and parasitic diseases that humans get from animals are hard to transmit between people, viruses mutate far faster and are more easily passed on to others. In the fall of 2014, the deadly Ebola virus jumped from an unknown animal to a two-year-old boy in Guinea. It quickly spread to those around him and began terrorizing West African nations; by April 2016, more than 11,000 people had died. Researchers now believe that fruit bats were the origin of this zoonotic disease—which refers to any disease that makes the jump from animals to humans (or vice versa). Today, 75 percent of all new or emerging infectious diseases are zoonotic.
So, how do we prevent future virus outbreaks? It’s clear. Protect nature: its wildlife and natural habitats.
Diverse, natural ecosystems dampen disease
Sadly, biodiversity (from ecosystems to genes to species) is declining faster than at any other time in human history.
Natural ecosystems function similarly to the human body: when they are robust with diverse species and healthy with space for animal populations, they are more resistant to disease. Thriving ecosystems also provide a variety of benefits to surrounding human communities, from fertile soil to food to fresh water.
However, when human activities, such as logging and mining, disrupt and degrade these ecosystems, animals are forced closer together. They are then more likely to become stressed or sick and be in closer proximity to human settlements. In diverse ecosystems well separated from human habitations, viruses ebb and flow without ever having a chance to make leaps between species. But as deforestation drives wild animals out of their natural habitats and closer to human populations, those protections begin to break down. In these conditions, diseases bounce back and forth between wildlife populations and us.
Disrupted ecosystems tend to lose their biggest predators first; and what they leave behind are smaller animals that live fast, reproduce in large numbers and have immune systems more capable of carrying disease without succumbing to it. When there are only a few species left, they get really good at carrying disease. And when those populations prosper near people, there may be nothing between a deadly pathogen and all of humanity.
For example, the Ebola virus emerged when land-use changes and altered climatic conditions in Africa forced bats and chimpanzees together around concentrated areas of food resources. The 1994 Hendra virus is associated with urbanization of fruit bats following habitat loss.
The United States provides another example. As forest habitats of opossums have become fragmented, these animals’ populations have declined. Opossums eat ticks and can resist the pathogen that causes Lyme disease. So, what happens when their habitats are bulldozed and cut? The ticks hop aboard the white-footed mouse, a species less adept at killing piggybacking ticks and less reliant on the forest for survival. And just like that, the biological buffer between the Lyme bacterium and humans is removed from the scene.
Researchers have been warning for decades that animal-borne illnesses are going to become more frequent due to the rapid destruction of nature. In fact, almost half of the new diseases that jumped from animals to humans after 1940 can be traced to agriculture, changes in land use or wildlife hunting. Ebola, Lyme, MERS, SARS, West Nile and others all fit the profile. There may be 10,000 mammalian viruses potentially dangerous to people.
Not only is animal biodiversity desirable, but plant diversity, as well. For instance, the rare Madagascar rose periwinkle, Catharanthus roseus, contains compounds useful as medicine for childhood leukemia. An estimated 50,000 to 70,000 plant species are harvested for traditional or modern medicine, while around 50 percent of modern drugs have been developed from natural products that are threatened by biodiversity loss.
Wide arrays of wildlife welcome wellness
Wildlife, too, needs to be protected if we want to safeguard ourselves. Authors of a 2013 paper published in the science journal Nature found that greater biodiversity in large-scale ecosystems, such as forests or grasslands, may also provide a better defense against diseases, including those that affect humans.
The paper’s authors discovered that the richer the assortment of amphibian species in a pond, the more protection that community of frogs, salamanders and toads has against a parasitic infection that can cause severe deformities, including the growth of extra legs. The results showed that ponds with half a dozen amphibian species had a 78 percent reduction in parasite transmission compared to ponds with just one amphibian species. The researchers concluded that the entire set of species in a community affects susceptibility to disease. Greater biodiversity definitely reduces the number of amphibian infections and the number of deformed frogs.
Removing a species through culling can also have health consequences for us. When you eliminate some but not all of the animals, you increase the level of a virus within a population because those individuals are still circulating it. This is known as the dilution effect, which hypothesizes that a higher rate of species richness creates a buffer against zoonotic pathogens.
Culling isn’t the only dangerous practice we humans have perpetrated on wildlife. Wild markets and the illegal wildlife trade pose some of the clearest threats to animal and human health. Taking disparate animals out of their various native environments and penning them together puts them in contact with other species—and other diseases—that they likely would have never encountered naturally in the wild. Wild animal markets that sell a variety of exotic species in one place are the perfect breeding ground for rare, zoonotic diseases. This exchange of wildlife and wildlife parts is also devastating to nature because it decimates species populations, such as elephants and rhinos, which are critical to the health of their respective ecosystems.
Wildlife biodiversity can restrain pathogens before they ever leave the wild. But under current conditions, more than 1 million species are at risk of extinction due to human activities.
Climate change causes catastrophes
What’s more, human-caused climate change plays a part in exacerbating pandemics. Along with natural habitat and wildlife loss, shifting climate zones increases our vulnerability to a range of health threats. As the world warms, wildlife is forced to migrate to new places, where they interact with other species they haven’t previously encountered, increasing the risk of new diseases emerging.
We know that in the late 1990s in Malaysia, the outbreak of Nipah virus was a result of forest fires and drought which had caused fruit bats, the natural carriers of the virus, to move from the forests to pig farms. Infected pigs then infected pig farmers, who infected others, spreading the disease.
Climate change has caused human displacement, which alters and accelerates the transmission patterns of infectious diseases such dengue fever, malaria and the Zika virus. Movements of large groups of people to new locations, often under poor conditions, increases their vulnerability to such biological threats.
Climate change is also responsible for massive fires across the planet. Earlier this year, more than half of the Australian population was exposed to health harm for weeks when life-threatening bushfires created a blanket of smoke pollution. More than 400 people died as a result. Air pollution particles act as transport for pathogens, contributing to the spread of infectious diseases and viruses across large distances.
Conservationist Carson calls the coming of COVID-19
It’s not like we didn’t know that a disease like COVID-19 was coming. In 2015, I wrote an article titled Linking Climate Change to Personal Health: Game Changer?, in which I discussed framing global warming as a public health issue, rather than as an environmental or national security problem in order to get people to more easily and quickly connect with the crisis. In 2017, Smithsonian Magazine ran an article titled Can Saving Animals Prevent the Next Deadly Pandemic? And in 2018, disease ecologist Dr. Peter Daszak, a contributor to the World Health Organization Register of Priority Diseases, coined the term Disease X. This described a then-unknown pathogen predicted to originate in animals and cause a “serious international epidemic.” COVID-19 is Disease X.
We’ve been lucky. The past 20 years of disease outbreaks could be viewed as a series of near-miss catastrophes. But we’ve also been unfortunate, because that may have led to complacency rather than the increased vigilance that’s necessary to control outbreaks. Perhaps the seriousness of our current situation will make us finally understand that the biodiversity crisis, the climate change crisis and the COVID-19 crisis are deeply connected. The state of the environment affects the transmission of infectious diseases, and that means we must adopt a holistic view of public health that includes the health of the natural environment.
We need to reimagine our relationship with nature. For a long time, nature was resilient and robust, so we assumed we could do anything we wanted to it and it would bounce back. Due to population growth and overexploitation, however, we’ve reached a point where what we do to nature now can permanently impact it. There’s a consistent pattern: when biodiversity decreases and wild spaces vanish, pathogens rage, putting humans, other animals—both wild and domestic—and plants at risk.
The collision course with nature that we’re on has to stop, for as pioneering, 20th-century conservationist Rachel Carson argued, a war against nature is inevitably a war against ourselves.
Here’s to finding your true places and natural habitats,