'Tip of the iceberg':
Is our destruction of nature responsible for Covid-19?
As habitat and biodiversity loss increase globally, the coronavirus outbreak may be just the beginning of mass pandemics
Mayibout 2 is not a healthy place. The 150 or so people who live in the village, which sits on the south bank of the Ivindo River, deep in the great Minkebe Forest in northern Gabon, are used to occasional bouts of diseases such as malaria, dengue, yellow fever and sleeping sickness. Mostly they shrug them off.
But in January 1996, Ebola, a deadly virus then barely known to humans, unexpectedly spilled out of the forest in a wave of small epidemics. The disease killed 21 of 37 villagers who were reported to have been infected, including a number who had carried, skinned, chopped or eaten a chimpanzee from the nearby forest.
I travelled to Mayibout 2 in 2004 to investigate why deadly diseases new to humans were emerging from biodiversity “hotspots” such as tropical rainforests and bushmeat markets in African and Asian cities.
It took a day by canoe and then many hours along degraded forest logging roads, passing Baka villages and a small goldmine, to reach the village. There, I found traumatised people still fearful that the deadly virus, which kills up to 90% of the people it infects, would return.
Villagers told me how children had gone into the forest with dogs that had killed the chimp. They said that everyone who cooked or ate it got a terrible fever within a few hours. Some died immediately, while others were taken down the river to hospital. A few, like Nesto Bematsick, recovered. “We used to love the forest, now we fear it,” he told me. Many of Bematsick’s family members died.
Only a decade or two ago it was widely thought that tropical forests and intact natural environments teeming with exotic wildlife threatened humans by harbouring the viruses and pathogens that lead to new diseases in humans such as Ebola, HIV and dengue.
But a number of researchers today think that it is actually humanity’s destruction of biodiversity that creates the conditions for new viruses and diseases such as Covid-19, the viral disease that emerged in China in December 2019, to arise – with profound health and economic impacts in rich and poor countries alike. In fact, a new discipline, planetary health, is emerging that focuses on the increasingly visible connections between the wellbeing of humans, other living things and entire ecosystems.
Is it possible, then, that it was human activity, such as road building, mining, hunting and logging, that triggered the Ebola epidemics in Mayibout 2 and elsewhere in the 1990s and that is unleashing new terrors today?
“We invade tropical forests and other wild landscapes, which harbour so many species of animals and plants – and within those creatures, so many unknown viruses,” David Quammen, author of Spillover: Animal Infections and the Next Pandemic, recently wrote in the New York Times. “We cut the trees; we kill the animals or cage them and send them to markets. We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.”
Research suggests that outbreaks of animal-borne and other infectious diseases such as Ebola, Sars, bird flu and now Covid-19, caused by a novel coronavirus, are on the rise. Pathogens are crossing from animals to humans, and many are able to spread quickly to new places. The US Centers for Disease Control and Prevention (CDC) estimates that three-quarters of new or emerging diseases that infect humans originate in animals. Some, like rabies and plague, crossed from animals centuries ago. Others, such as Marburg, which is thought to be transmitted by bats, are still rare. A few, like Covid-19, which emerged last year in Wuhan, China, and Mers, which is linked to camels in the Middle East, are new to humans and spreading globally. Other diseases that have crossed into humans include Lassa fever, which was first identified in 1969 in Nigeria; Nipah from Malaysia; and Sars from China, which killed more than 700 people and travelled to 30 countries in 2002–03. Some, like Zika and West Nile virus, which emerged in Africa, have mutated and become established on other continents.
Kate Jones, chair of ecology and biodiversity at UCL, calls emerging animal-borne infectious diseases an “increasing and very significant threat to global health, security and economies”.
In 2008, Jones and a team of researchers identified 335 diseases that emerged between 1960 and 2004, at least 60% of which came from animals.
Increasingly, says Jones, these zoonotic diseases are linked to environmental change and human behaviour. The disruption of pristine forests driven by logging, mining, road building through remote places, rapid urbanisation and population growth is bringing people into closer contact with animal species they may never have been near before, she says. The resulting transmission of disease from wildlife to humans, she says, is now “a hidden cost of human economic development. There are just so many more of us, in every environment. We are going into largely undisturbed places and being exposed more and more. We are creating habitats where viruses are transmitted more easily, and then we are surprised that we have new ones.”
Jones studies how changes in land use contribute to the risk. “We are researching how species in degraded habitats are likely to carry more viruses which can infect humans,” she says. “Simpler systems get an amplification effect. Destroy landscapes, and the species you are left with are the ones humans get the diseases from.”
“There are countless pathogens out there continuing to evolve which at some point could pose a threat to humans,” says Eric Fevre, chair of veterinary infectious diseases at the University of Liverpool’s Institute of Infection and Global Health. “The risk [of pathogens jumping from animals to humans] has always been there.”
The difference between now and a few decades ago, Fevre says, is that diseases are likely to spring up in both urban and natural environments. “We have created densely packed populations where alongside us are bats and rodents and birds, pets and other living things. That creates intense interaction and opportunities for things to move from species to species,” he says.
Tip of the iceberg
“Pathogens do not respect species boundaries,” says disease ecologist Thomas Gillespie, an associate professor in Emory University’s department of environmental sciences, who studies how shrinking natural habitats and changing behaviour add to the risk of diseases spilling over from animals to humans.
“I am not at all surprised about the coronavirus outbreak,” he says. “The majority of pathogens are still to be discovered. We are at the very tip of the iceberg.”
Humans, says Gillespie, are creating the conditions for the spread of diseases by reducing the natural barriers between host animals – in which the virus is naturally circulating – and themselves. “We fully expect the arrival of pandemic influenza; we can expect large-scale human mortalities; we can expect other pathogens with other impacts. A disease like Ebola is not easily spread. But something with a mortality rate of Ebola spread by something like measles would be catastrophic,” Gillespie says.
Wildlife everywhere is being put under more stress, he says. “Major landscape changes are causing animals to lose habitats, which means species become crowded together and also come into greater contact with humans. Species that survive change are now moving and mixing with different animals and with humans.”
Gillespie sees this in the US, where suburbs fragment forests and raise the risk of humans contracting Lyme disease. “Altering the ecosystem affects the complex cycle of the Lyme pathogen. People living close by are more likely to get bitten by a tick carrying Lyme bacteria,” he says.
(To be contd)