Deforestation And The Next Pandemic

We all know the classic western movie scene: cowboys ride through a herd of cows, moving them across endless open prairie with snow-capped mountains shining in the distance. But those days are long gone. Little easily-available grassland remains across the globe, so those who want to raise cows or other large animals must convert another type of habitat. Since about a third of global land cover is forest, that’s often what stands in the way of more grazing area. We know that deforestation causes severe environmental damage, but there’s another dark side: in the process of clearing forests, humans and domestic animals encounter insects and wildlife which carry previously unknown pathogens. Think SARS-CoV-2, the cause of the current pandemic.

COVID-19, the disease caused by SARS-CoV-2, has been traced to a Huanan “wet market” in Wuhan, China. The SARS-Cov-2 coronavirus likely jumped from animal to human in that context, and though we aren’t yet 100% certain which animal or animals were part of this chain, evidence points towards bats and a scaly mammal called a pangolin. The most illegally traded mammal in the world, pangolins are valued both for their meat and for the purported (and unproven) medicinal properties of their scales. The 2002 SARS coronavirus outbreak took a similar path, moving from horseshoe bats to civets and then to humans.

A disease that moves between animals and humans is called a “zoonosis”. In the case of new, or “novel”, zoonoses, we have no previous immunity, so they can pose a significant health threat. Wet markets offer zoonotic viruses a prime opportunity to jump across species because of the proximity of live animals, including wildlife. To infect a new host, a virus must be able to physically invade the host and find a way into its cellular machinery to replicate itself. According to the U.S. Centers for Disease Control (CDC), an estimated 60% of infectious diseases, among them rabies, Lyme, and  West Nile, originally came from animals. And perhaps more ominously, three-quarters of new or emerging infectious pathogens are zoonotic. 

Mosquitos are one particularly well-known culprit in disease transmission. Clearing tall trees in a forest or jungle opens up the forest floor to sunlight and disrupts streams. This allows the growth of larvae from the pooling of water. Researchers are using a variety of models and surveillance technology to determine whether and how forest clearing translates to changes in malaria incidence. One such study in Borneo found that new malaria infections followed the pattern of tree clearing  for palm oil plantations when humans began to work on the edges of the newly-cleared areas where the mosquitos thrived. Cases of malaria have surged in parts of Africa, Asia, and South America where rainforest has been cleared, typically for agricultural uses. And in years when more land is cleared, there are spikes of leptospirosis and dengue fever as well. 

Then there are bats. It took years of research to uncover their role in the 2002-2003 SARS virus outbreak. And they may also be implicated in Ebola. But we have even more to fear from the Nipah virus, a lesser known disease that also originates in bats. The Nipah virus first emerged in the late 1990’s in Malaysia. It is a neurological disease with no known cure that killed 40% of its victims. Areas where tropical forests were cleared for pig farms became ground zero for the outbreak: both the pigs and the bats ate mangoes in nearby orchards, allowing transmission of Nipah into pigs and then to humans. This serves as a good illustration of how  zoonotic disease arises from activities that bring humans and animals used for food into contact with wildlife. 

We can find another example in smallpox. This pathogen caused some of the earliest plagues. It likely arose from forest clearing in tropical Asia when animal husbandry was first beginning. Land use change brings humans into areas where wildlife live. Deforestation fragments habitats so that the forest becomes interspersed with agricultural lands and human settlements. This “edge effect” promotes interactions between pathogens, vectors such as insects and hosts. Cleared areas thus may become home to domestic species such as feral pigs, goats, rats, mice, dogs and cats which then become potential pathogen reservoirs and vectors of disease spread. Raising farm animals in these fragmented habitats where they mix with wild animals and then bringing them into markets creates an ideal environment for zoonoses.

According to the United Nations Food and Agriculture Organization (FAO), 26% of the earth’s land surface is used to graze animals used for food. A third of the planet’s arable land grows feed crops for animals. Every year, we lose 2-3% of Earth’s forests, the majority in tropical countries. The destruction of a forest usually starts with road construction. These new roads allow logging and mining in the forest interior. Then, commercial or subsistence farmers use the new roads as access points to new land which they clear to grow crops. The nutrient-poor soils can only sustain cropping for a few years. Then, the farmers move on and the ranchers move in, at least for a few more years until the land has no more to offer. Over the past 25 years, trees were cleared from an area the size of India. Because the investment risk is low, even poor-quality land that is not very productive produces cows who can be very profitable. 

Indeed, in South America, researchers estimate that 71% of rainforest clearing has been done to create cow ranches. While most of the newly cleared forest becomes pasture, there is one other often-overlooked outcome from forest clearing in the region. Part of the cleared land came under tillage for soybeans to feed animals. Soy is now the largest single crop grown in South America. Over the past two decades the trade in soy has become one of the biggest international commodity flows in the world. China is using the soy to dramatically expand intensive animal feeding operations. Other Asian countries have followed suit, taking advantage of South America’s land availability.

The COVID-19 pandemic highlights the dangers of mixing humans, domestic animals, and wildlife. Given how pathogens can mutate, forests and jungles can give rise to a potentially limitless number of diseases for which we have no immunity. Our best course of action is to steer clear of these areas. But given that meat consumption is on an upward trajectory and more land is needed to meet this demand, the prudent course of action is not the likely course of action. 

Population increases coupled with rising incomes will drive global per capita meat consumption from 43 kilograms (95 pounds) to around 76 kilograms (166 pounds), by mid-century. This represents a 76% increase over current levels. About one-third of current meat consumption is pork, another third is chicken, 20% is beef and the remainder are sheep, goats, and other animals. The United Nations (UN) estimates that we will double the amount of chicken we eat and increase our beef and pork consumption by 69% and 42%, respectively. And for much of the world’s populations, meat is cheaper today than it has ever been, relative to their income. Indeed, growth in demand is greatest in middle-income nations, while stable to declining in high-income countries. China, in particular, with its rapidly expanding middle class and 1.4 billion citizens, is a prime driver of these trends. 

Yet there is one piece of good news here. Since it’s human behavior that drives the emergence and spread of zoonoses, it’s within our power to change that behavior. If we reduce demand for meat, we lessen the pressure to bring more land into production for pastures and feed crops. That can help to reduce the risks of zoonotic disease transmission. This is where animal advocates can play a role. There are studies showing that the health motive can increase the adoption of a more plant-based diet. Traditionally, that’s meant things like weight management, blood cholesterol, hypertension and so forth. That health motive can now encompass reducing the risks of pandemics from zoonotic disease. We need to get the message out about the link between pandemic risk and meat consumption. Whether it’s Meatless Monday campaigns or vegan awareness, our message is now more important than ever.