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Human activities fuel diseases?
About ten years ago, the British government first reported a link between the cattle disease bovine spongiform encephalopathy (BSE) and its human equivalent Creutzfeldt-Jakob disease (CJD); five years ago, the cull began of millions of sheep and cows suspected to have foot and mouth disease; and three years ago, severe acute respiratory syndrome (Sars) threatened global health. Now poultry farmers around the world are on full alert as country after country reports the virulent H5N1 avian influenza virus in wild birds, which could cross over to humans.
As dead swans are found with H5N1, and Europe locks up its poultry, a consensus is emerging among scientists, ecologists and human health experts that this strain of avian flu, as well as diseases such as monkeypox, HIV/Aids, West Nile virus, Ebola, Sars, BSE and Lyme disease are emerging and crossing more easily to humans because of environmental changes taking place and the intensification of farming. Diseases are then spread rapidly around the world with the globalisation of trade and aviation.
Diseases have spread from wildlife to humans throughout history but we now interact with animals in a very different way, says Danielle Nierenberg, a researcher with the US Worldwatch Institute. “In the last 40 years the world has gone through a livestock revolution, not unlike what happened to crops with the green revolution,” she says.
Since 1961, she explains, worldwide livestock has increased 38 per cent, to about 4.3 billion today. The global poultry population has quadrupled in that time, to 17.8 billion birds, and the number of pigs has roughly trebled to 2 billion. As the numbers of animals bred for food have vastly grown in a very short period, humankind’s relationship with them has changed.
“Raising animals has morphed into an industrial endeavour that bears little relation to landscape or natural tendencies of the animals. Wherever (industrial farming) is introduced it creates ecological and public health disasters,” she says.
Others argue that intensive confinement of animals promotes emerging viruses, stokes the development of antibiotic-resistant strains of bacteria and can transform animals into disease “factories”.
According to Hans-Gerhard Wagner, an officer of the UN Food and Agriculture Organisation based in Thailand, the “intensive industrial farming of livestock is now an opportunity for emerging diseases”.
Susceptible to disease
Caroline Lucas, Green MEP for south-east England, says intensive farming now plays a major role in the spread of diseases. “There is a reduction in the diversity of breeds in order to have the fastest growth, and animals are becoming more susceptible to diseases because of the way they are bred and kept. The search for profits leads to animals and then humans becoming more vulnerable. Our current policies are encouraging farming that overlooks basic husbandry.”
Ecologist Vandana Shiva says: “Food hazards have increased with industrialisation of food production and processing. On a global scale, new diseases are emerging and more virulent forms of old diseases are growing as globalisation spreads factory farming and industrial processing and agriculture. Disease epidemics and food hazards are the outcome of food production methods based on hazardous inputs and processes.”
Peter Daszak, director of the Consortium for Conservation Medicine, which strives to understand the link between human alterations to the environment, wildlife disease, public health and conservation, says emerging diseases such as the H5N1 strain of avian flu are causing a crisis of public health.
Daszak, who helped connect Asian bats in China with Sars, says diseases such as Sars, Ebola, BSE, CJD, HIV/Aids and H5N1 bird flu are entirely driven by environmental change, which is almost always caused by humans. Because humans share so many pathogens with animals, humans’ impact in driving wildlife diseases, in turn, threatens public health.
A consensus is emerging among scientists that this strain of avian flu, as well as diseases such as monkeypox, HIV/Aids, West Nile virus, Ebola, Sars, BSE and Lyme disease are emerging and crossing more easily to humans because of environmental changes
The Sars virus, which killed at least 700 people, emerged from the trade in wildlife for food and was spread by air travel. It is similar situation with bird flu, Daszak says.
“All these diseases are driven by human activities, like roadbuilding, agricultural changes, population movements, people moving to cities. Environmental change, linked to demography and the unprecedented speed at which environmental change is taking place, are responsible.
“The global poultry industry is clearly linked to avian influenza. It would not have happened without it. There has been an explosion in the global poultry industry. There has always been a close link between people and poultry,” he says.
Once an emerging disease such as H5N1 avian flu breaks out, he says, globalisation in the form of greatly increased world trade and the growth of the aviation industry can spread it fast. “We are certain to see more and more of these diseases emerging with very high impacts on health and the economy.”
Keeping forests and other ecosystems intact could be the best protection humankind has against new diseases. Intrusions into the world’s areas of high biodiversity disturbs biological “reservoirs” and exposes people to new forms of infectious disease, says Diversitas, a group of scientists exploring biodiversity.
By diluting the pool of virus targets and hosts, biodiversity reduces their impact on humans and provides a form of global health insurance. “Biodiversity not only stores the promise of new medical treatments and cures, it buffers humans from organisms that cause disease,” says Anne Larigauderie, director of Diversitas.
Recently she urged doctors and ecologists to share knowledge more. “The medical community should invest more in understanding the environmental origins of viruses, and what can become diseases. Viruses are always there, in the forests or the fields. As the environment is disturbed, people have become closer to them and they become diseases.
“The best security against (diseases like H5N1 bird flu) is conservation, and awareness by governments and the medical community that these diseases are not medical problems to begin with. Nature keeps them in check. Once they are in humans then it is almost too late.”
“As the human population continues to grow, our needs for space and resources result in further encroachment into a diminishing natural world,” says Andrew Cunningham — a reader in wildlife epidemiology at the Institute of Zoology — in the British Medical Journal.
“Through emerging infectious diseases, the medical, veterinary, and wildlife conservation professions share a common agenda. The problem is not small, and tackling it will not be easy, but recognising a common problem is a start.” — Dawn/The Guardian News Service
See how easy it is to drift into speculating about the worst possible eventuality? Avian flu does not yet pose any direct threat to humans, but the worst-case scenario is that it might mutate and trigger a flu pandemic that would put millions of human lives at risk.
An enthusiasm for ignoring the whole range of probabilities to fix on the worst possible outcome haunts the popular consciousness, and has been flummoxing social scientists for more than a decade. In Europe, it has been filed by portentous European sociologists under the heading of “risk society”. In America, after 9/11, they call it “the dread factor”.
But according to the American sociologist Lee Clarke, author of Worst Cases: Terror and Catastrophe in the Popular Imagination, the dread factor is less irrational than we might think. Ushering us through a catalogue of near misses and outrageously unlikely accidents, Clarke contends that disasters are more normal than we think, and that worst cases abound.
He distinguishes worst-case thinking from the conventional approach of probabilistic thinking. The wisdom of worst-case thinking, he says, is why we’re urged to wear seatbelts and not to smoke. To ignore worst cases, he argues, would also be elitist, as it ignores lay opinions about how to calculate risk. Worst-case scenarios, he argues, can motivate us to action, protect us from hubris and teach us a little humility.
Clarke’s argument is intriguing, but flawed. A decision-making rule that evaluates every course of action in terms of its worst possible outcome is already known to game theorists as the maximin principle, and it is common ground that it leads to perverse results.
Imagine that I am simultaneously offered two jobs, one tedious and badly paid in London and another glamorous and lucrative in New York.
The New York job means that I will have to fly there, and there is a small possibility that my plane might crash. Weighing up my options with the help of the maximin rule, I should prefer the London job, as the worst possible outcome of accepting the post in New York is that I wind up in an economy class watery grave.
The trouble with the maximin principle is that it means my decisions turn on a worst-case scenario irrespective of the likelihood that such a scenario will ever come to pass. Worst-case scenario is that when I next take a walk I will be run over by a double-decker bus. Worst-case scenario is that on a long-haul flight I will find myself sitting next to Richard Branson.
Worst-case scenarios need to be taken into account, as Clarke says, but they are not in themselves a reliable guide to action and should always be balanced against the likelihood that they will come to pass. Before you stock up on antiviral medicine, shoot the cat and head for the hills, remember to take a deep breath and weigh up the odds. — James Harkin/The Guardian
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