Bird flu: intensive farming link
John VIDAL
BIRD FLU: Animal farming and man's intrusion into the environment are
major factors in the spread of new diseases.
INDIA: An Indian man carrying chickens walks on the outskirts of New
Delhi February 19. India reported its first suspected human death
from bird flu on Sunday, a day after announcing its first infections
of the H5N1 flu virus in poultry. REUTERS
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Ten years ago next month, the United Kingdom's Government first
reported a link between the cattle disease bovine spongiform
encephalopathy (BSE) and its human equivalent Creutzfeldt-Jakob disease
(CJD); five years ago this week, 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 it is feared could cross 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 U.S. 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 (Member of the European Parliament) 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.
Mr. 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.
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, Mr. 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.
High impact on health
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 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.
This week 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."
- Guardian Newspapers Limited 2006 (The Hindu) |