Swine Flu is Related to Virus Born on U.S. Hog Factories in 1998
April 29, 2009
Crowded conditions on factory farms create breeding grounds for new
viruses. ©iStockphotoBy Michael Greger, M.D.
Factory farming and long-distance live animal transport apparently led to
the emergence of the ancestors of the current swine flu threat.
A preliminary analysis of the H1N1 swine flu virus isolated from human cases
in California and Texas reveals that six of the eight viral gene segments
arose from North American swine flu strains circulating since 1998, when a
new strain was first identified on a factory farm in North Carolina.
*Plaguing People and* *Pigs*
The worst plague in human history was triggered by an H1N1 avian flu virus,
which jumped the species barrier from birds to
humans[1]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>and
went on to kill as many as 50 to 100 million people in the 1918 flu
pandemic.[2]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>We
then passed the virus to pigs, where it has continued to circulate,
becoming one of the most common causes of respiratory disease on North
American pig farms.[3]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
<ebergst...@humanesociety.org> For media interviews with Dr. Michael
Greger, please contact Liz Bergstrom at ebergst...@humanesociety.org or
301-258-1455. ©The HSUS In August 1998, however, a barking cough resounded
throughout a North Carolina pig factory in which all the thousands of
breeding sows fell
ill.[4]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>A
new swine flu virus was discovered on that factory farm, a human-pig
hybrid virus that had picked up three human flu genes. By the end of that
year, the virus acquired two gene segments from bird flu viruses as well,
becoming a never-before-described triple reassortment virus—a hybrid of a
human virus, a pig virus, and a bird virus—that triggered outbreaks in
Texas, Minnesota, and
Iowa.[5]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
Within months, the virus had spread throughout the United States. Blood
samples taken from 4,382 pigs across 23 states found that 20.5% tested
positive for exposure to this triple hybrid swine flu virus by early 1999,
including 100% of herds tested in Illinois and Iowa, and 90% in Kansas and
Oklahoma.[6]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>According
to the current analysis, performed at the Columbia University's
Center for Computational Biology and Bioinformatics, it is from this pool of
viruses that the current swine flu threat derives three-quarters of its
genetic material.[7]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
*Tracing the Origins of Today's Virus*
Since the progenitor of the swine flu virus currently threatening to trigger
a human pandemic has now been identified, it is critical to explore what led
to its original emergence and spread. Scientists postulate that a human flu
virus may have starting circulating in U.S. pig farms as early as 1995, but
"by mutation or simply by *obtaining a critical density*, caused disease in
pigs and began to spread rapidly through swine herds in North America.
[emphasis added]"[8]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>It
is therefore likely no coincidence that the virus emerged in North
Carolina, the home of the nation’s largest pig production operation. North
Carolina has the densest pig population in North America and reportedly
boasts more than twice as many corporate pig mega-factories as any other
state.[9]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
The year of emergence, 1998, was the year North Carolina's pig population
hit ten million, up from two million just six years
earlier.[10]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>Concurrently,
the number of pig farms was decreasing, from 15,000 in 1986 to
3,600 in 2000.[11]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>How
can five times more animals be raised on almost five times fewer
farms?
By crowding about 25 times more pigs into each operation. In the 1980s, more
than 85% of all North Carolina pig farms had fewer than 100 animals.
By the end of the 1990s, operations confining more than 1,000 animals
controlled about 99% of the state's pig
population.[12]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>Given
that the primary route of swine flu transmission is thought to be the
same as human flu—via droplets or aerosols of infected nasal
secretions[13]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>—it's
no wonder experts blame overcrowding for the emergence of new flu virus
mutants.
*Intensive Crowding and Long-Distance Transport*
Starting in the early 1990s, the U.S. pig industry restructured itself after
Tyson's profitable chicken model of massive industrial-sized units. As a
headline in the trade journal National Hog Farmer announced, "Overcrowding
Pigs Pays—If It's Managed
Properly."[14]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>The
majority of U.S. pig farms now confine more than 5,000 animals each. A
veterinary pathologist from the University of Minnesota stated the obvious
in Science: "With a group of 5,000 animals, if a novel virus shows up it
will have more opportunity to replicate and potentially spread than in a
group of 100 pigs on a small
farm."[15]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
Dr. Robert Webster, one of the world's leading experts of flu virus
evolution, blames the emergence of the 1998 virus on the "recently evolving
intensive farming practice in the USA, of raising pigs and poultry in
adjacent sheds with the same staff," a practice he calls
"unsound."[16]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>North
Carolina is also one of the nation's largest poultry producers,
slaughtering nearly three-quarters of a billion
chickens[17]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>and
confining enough hens to produce nearly 3 billion eggs.
[18]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
Once the new viral mutant appeared in 1998, the rapid dissemination across
the country has been blamed on long-distance live animal
transport.[9]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>In
the United States, pigs travel coast to coast. They can be bred in
North
Carolina, fattened in the corn belt of Iowa, and slaughtered in California.
[20]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>While
this may reduce short-term costs for the pork industry, the highly
contagious nature of diseases like influenza (perhaps made further
infectious by the stresses of transport) needs to be considered when
calculating the true cost of long-distance live animal transport.
*"A Recipe for Disaster"*
The remaining two gene segments of the H1N1 swine flu virus now spreading in
human populations around the world appear to come from a swine flu viral
lineage circulating in Eurasia, where similar conditions may be to blame.
"Influenza [in pigs] is closely correlated with pig density," said a
European Commission-funded researcher studying the situation in
Europe.[21]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>As
such, Europe's rapidly intensifying pig industry has been described in
*Science* as "a recipe for
disaster."[22]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>Some
researchers have speculated that the next pandemic could arise out of
"Europe's crowded pig
barns."[23]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>In
Europe in 1993, a bird flu virus had adapted to pigs, acquiring a few
human flu virus genes and infected two young Dutch children, displaying
evidence of limited human-to-human
transmission.[24]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
The European Commission's agricultural directorate warns that the
"concentration of production is giving rise to an increasing risk of disease
epidemics."[25]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>Concern
over epidemic disease is so great that Danish laws have capped the
number of pigs per farm and put a ceiling on the total number of pigs
allowed to be raised in the
country.[26]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>No
such limit exists in the United States.
*Warnings Unheeded*
The public health community has been warning about the risks posed by
factory farms for years. More than five years ago, in 2003, the American
Public Health Association, the largest and oldest association of public
health professionals in the world, called for a moratorium on factory
farming.[27]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>In
2005, the United Nations urged that "[g]overnments, local authorities
and
international agencies need to take a greatly increased role in combating
the role of factory-farming," which, they said, combined with live animal
markets, "provide ideal conditions for the [influenza] virus to spread and
mutate into a more dangerous
form."[28]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
Last April, the Pew Commission on Industrial Farm Animal Production released
its final report. The prestigious, independent panel chaired by a former
Kansas Governor and including a former U.S. Secretary of Agriculture, former
Assistant Surgeon General, and the Dean of the University of Iowa College of
Public Health, concluded that industrialized animal agriculture posed
"unacceptable" public health risks: "Due to the large numbers of animals
housed in close quarters in typical [industrial farm animal production]
facilities there are many opportunities for animals to be infected by
several strains of pathogens, leading to increased chance for a strain to
emerge that can infect and spread in
humans."[29]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
Specific to the veal crate-like metal stalls that confine breeding pigs like
those on the North Carolina factory from which the first hybrid swine flu
virus was discovered in North America, the Pew Commission asserted that
"[p]ractices that restrict natural motion, such as sow gestation crates,
induce high levels of stress in the animals and threaten their health, which
in turn may threaten human
health."[30]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>Unfortunately
we don't tend to "shore up the levees" until after the
disaster, but now that we know swine flu viruses can evolve to efficiently
transmit human-to-human we need to follow the Pew Commission's
recommendations to abolish extreme confinement practices like gestation
crates as they're already doing in Europe, and to follow the advice of the
American Public Health Association to declare a moratorium on factory farms.
*A "Reservoir of Viruses" in the U.S.*
With massive concentrations of farm animals within whom to mutate, these new
swine flu viruses in North America seem to be on an evolutionary fast track,
jumping and reassorting between species at an unprecedented
rate.[31]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>This
reassorting, Webster's team concludes, makes the 65 million strong
U.S.
pig population an "increasingly important reservoir of viruses with human
pandemic potential."[32]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>"We
used to think that the only important source of genetic change in
swine
influenza was in Southeast Asia," said Christopher Olsen, a molecular
virologist at the University of Wisconsin, Madison. Now, "we need to look in
our own backyard for where the next pandemic may
appear."[33]<https://wadmin3.getactive.com/preview%21www.hsus.org/farm/news/ournew...>
*Dr. Michael Greger is director of public health and animal agriculture for
The Humane Society of the United States.*
------------------------------
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[31]<https://wadmin3.getactive.com/preview%21www.hsus.org/admin/item/actio...>Wuethrich
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http://birdflubook.org/resources/WUETHRICH1502.pdf.
[32]<https://wadmin3.getactive.com/preview%21www.hsus.org/admin/item/actio...>Webby
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[33]<https://wadmin3.getactive.com/preview%21www.hsus.org/admin/item/actio...>Wuethrich
B. 2003. Chasing the fickle swine flu. Science 299:1502-5.
http://BirdFluBook.org/resources/WUETHRICH1502.pdf.
--
Michael Greger, M.D.
Director, Public Health and Animal Agriculture
The Humane Society of the United States
2100 L St., N.W.
Washington, DC 20037
direct line: (202) 676-2361
fax: (202) 676-2372
http://www.birdflubook.org
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