At first blush, the dangers looming due to climate change are typified by very large phenomena: bushfires, floods, hurricanes, rising oceans, that sort of thing.
To American scientist, physician and biodefence expert Laura Kahn, however, one of the biggest dangers facing humanity is not gargantuan, but invisible to the naked eye.
“The great challenge we face in the 21st century is figuring out how to sustainably feed ourselves, in a warming planet, without unleashing many more deadly zoonotic diseases upon ourselves,” she says.
Zoonotic diseases are those that jump from one species to another. They have always been part of human history – the plague, for instance, is caused by a zoonotic bacterium that leaps from fleas, and measles was originally a cattle virus called rinderpest – but urbanisation and population growth appear to be providing ever more frequent opportunities for bugs to cross over the species barrier.
A landmark 2005 study found that of all known human pathogens, 60% were zoonotic. The total was even higher – 75% — in the case of emerging infectious diseases.
In recent years, zoonotic diseases have spurred several worldwide public health emergencies, and cost a great number of lives. Examples include Ebola, SARS, MERS, West Nile and Zika. Terrible though their tolls have been, they are tiny compared to two of the commonest zoonoses around: influenza (which, depending on the strain, jumps from birds or swine) and HIV/AIDS, which crossed over from chimpanzees.
Some years ago, exploring possible alternative strategies to better manage the threat posed by zoonotic diseases, Kahn co-founded the One Health Initiative – a collaboration between physicians, veterinarians and other health professionals. Member organisations include the American Medical Association, the Centres for Disease Control and Prevention, the US department of Agriculture and the American Nurses Association.
“One Health recognises the close linkages between human, animal, and environmental health,” she explains.
“We’ve built up silos over the past century and focus primarily on humans. We must recognise that we don’t live in a vacuum. We are part of a dynamic, microbial world.”
The One Health approach, with its insistence that human wellbeing is indivisible from that of other species and the wider environment, may sound simply well-meaning and aspirational, but Kahn sees it as a bulwark against not merely unplanned epidemics, but also against the distinctly more anthropogenic threat of bio-warfare.
“Most of the agents of bioterrorism are zoonotic diseases as well,” she says. “There’s an overlap between emerging diseases and bioterrorism — the zoonotic connection.”
To this end, for six years up to 2009, she organised a series of seminars on biodefence, sponsored by the Carnegie Corporation and held at Princeton University.
From this experience, she wrote a book, Who’s In Charge?, examining leadership responses during “epidemics, bioterror attacks and other public health crises”.
And while the risk of a devastating biological warfare attack – whether by state actors or terrorists – is always present, Kahn is just as worried that the next pandemic might arise from the pure, simple and ugly fact that out species is rapidly filling up the world with its own microbe-filled manure.
“We need to understand how our microbial world works, and how our microbial bodies work,” she says.
“We also need to figure out what to do with all of our wastes. Humans and our domestic animals now make up around 98% of the mammalian zoomass on the planet.
“Much of human and animal manure gets spread onto agricultural fields as fertiliser. It leaches into the soil and waterways, causing soil and water contamination from heavy microbial overloading. This contributes to food-borne and waterborne illnesses. So, everything is connected.”
One way to tackle this problem, she says, is to take the One Health approach and make it both global and mandatory.
“The One Health concept must be integrated into the United Nation’s Sustainable Development Goals,” she says. “And One Health must be integrated into public health. Public health solely focuses on humans. We need to expand it and include the animals and environment, too.”
For Cosmos readers in the UK, Kahn is set to expand on these ideas when she gives a talk at the Centre for the Study of Existential Risk at Cambridge University later this month.
For those who can’t make it, she’s happy to sum up her theme.