Is there a link to nature’s destruction?
Only a decade or two ago it was widely thought that intact natural environments were the source of the pathogens that led to new diseases in humans such as Covid-19, the disease caused by a coronavirus that crossed over from wildlife to humans in China in December last year.
But a number of researchers now think it is actually humanity’s destruction of biodiversity which creates the conditions for new diseases. The discipline known as planetary health is emerging, focusing on links between people’s well-being and other living organisms and entire ecosystems.
Is it human activity, such as road building, mining, hunting and logging, that triggered past epidemics and is unleashing new terrors today?
Research suggests that outbreaks of infectious diseases such as Ebola, Sars, bird flu and Covid-19 are on the rise. Pathogens cross to humans from other animals and many can spread quickly to new sites.
The US Centers for Disease Control and Prevention estimates that three-quarters of “new or
‘Pathogens don’t respect the species boundaries. I am not surprised about Covid-19’ Thomas Gillespie Scientist
emerging” human diseases originate in nonhuman animals.
Kate Jones, a scientist and chair of ecology and biodiversity at University College London, says emerging animal-borne infectious diseases are an “increasing and very significant threat to global health, security and economies”.
In 2008 Jones and a team of researchers identified 335 diseases that had emerged between 1960 and 2004; at least 60% of those had come from other animals.
Increasingly, says Jones, these diseases are linked to environmental change and human behaviour. The disruption of pristine forests, for instance, is bringing people into closer contact with wild species they may never have been near before. The transmission of disease from wildlife to humans is a hidden cost of economic development.
Eric Fevre, chair of veterinary infectious diseases at the University of Liverpool, says: “There are just so many more of us, in every environment. We are going into largely undisturbed places. The risk [of pathogens jumping from other animals to people] has always been there.” The difference now though is that diseases are likely to spring up in both urban and natural environments. “We have created densely packed populations where alongside us are bat, rodents birds, pets, other living things. That creates intense interaction and opportunities for things to move from species to species.”
Thomas Gillespie, an associate professor in the environmental sciences department at Emory University, Atlanta, says: “Pathogens do not respect species boundaries. I am not at all surprised about the coronavirus outbreak. The majority of pathogens are still to be discovered. We are at the very tip of the iceberg.”
Humans, says Gillespie, create the conditions for the spread of diseases by reducing the natural barriers between virus host animals and themselves. “Major landscape changes are causing animals to lose habitats, which means species become crowded together and also come into greater contact with [us].”
Yet, according to Richard Ostfeld, senior scientist at the Cary Institute of Ecosystem Studies, in California, human health research seldom considers surrounding natural ecosystems.
"There's misapprehension among scientists and the public that natural ecosystems are the source of threats to ourselves. It’s a mistake. Nature poses threats, it is true, but it’s human activities that do the real damage. The health risks in a natural environment can be made much worse when we interfere with it.”
Felicia Keesing, professor of biology at Bard College, New York, studies environmental changes’ influence on exposure to infectious
diseases. “When we erode biodiversity we see a proliferation of the species most likely to transmit new diseases to us, but there’s also good evidence that those same species are the best hosts for existing diseases.”
Disease ecologists say pathogens also migrate to people from animals at markets selling fresh meat around the world. The market thought by the Chinese government to be the starting point of the Covid-19 pandemic was known to sell many wild creatures. “Wet markets make a perfect storm for cross-species transmission of pathogens,” says Gillespie.
But some scientists think bans on sales of live animals in urban areas or such markets are not the answer. Delia Grace, a senior epidemiologist with the International Livestock Research Institute, in Kenya, says: “These markets are essential sources of food for hundreds of millions of poor people.” Bans can force traders underground, where people may pay less attention to hygiene.
Change, according to Jones, should come from both rich and poor societies. Demand from the “global north” for resources leads to the ecological disruption that drives disease, she says. “We must think about global biosecurity, find the weak points and bolster the provision of healthcare in developing countries.”
Brian Bird, a research virologist at the One Health Institute, University of California Davis, says: “[The risks] were always present and have been there for generations. It is our interactions with that risk which must be changed. We are in an era now of chronic emergency. Diseases are more likely to travel farther and faster than before, which means we must be faster in our responses. It needs investments, change in human behaviour. We must listen to people at community level.”
Getting across the message about pathogens and disease to hunters, loggers, market traders and consumers, is key, Bird adds.
Fevre advocates rethinking urban infrastructure, and Bird stresses that the bottom line is to be prepared. “We can’t predict where the next pandemic will come from so we need mitigation plans to take into account the worst possible scenarios. The only certain thing is that the next one will certainly come.”
Timber stacked in Mindourou, Cameroon, with FSC sustainable certification. Transmission of animal-borne germs to people can follow forest clearance
▲ A wild bat for sale in Indonesia at one of the world’s many meat markets
▲ A lizard for sale at a market in the Democratic Republic of the Congo