Dr. Michael Greger is the director of public health and animal agriculture for The Humane Society of the United States , as well as the author of Bird Flu: A Virus of Our Own Hatching. Here's what he has to say about swine flu (H1N1) and the role of factory farms in it's evolution and spread.
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.
This genetic fingerprint, first released by Columbia University’s Center for Computation Biology and the Institute for Advanced Study in Princeton, has now been reportedly confirmed by researchers at the University of Edinburgh
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 and went on to kill as many as 50 to 100 million people in the 1918 flu pandemic. 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.
In August 1998, however, a barking cough resounded throughout a North Carolina pig factory in which all the thousands of breeding sows fell ill. 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.
Within months, the virus had spread throughout the United States. Blood samples taken from 4,382 pigs across 23 states found that 20.5 percent tested positive for exposure to this triple hybrid swine flu virus by early 1999, including 100 percent of herds tested in Illinois and Iowa, and 90 percent in Kansas and Oklahoma. 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.
Tracing the Origins of Today's H1N1 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]" 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.
The year of emergence, 1998, was the year North Carolina's pig population hit ten million, up from two million just six years earlier. Concurrently, the number of pig farms was decreasing, from 15,000 in 1986 to 3,600 in 2000. 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. 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 — it's no wonder experts blame overcrowding for the emergence of new flu virus mutants.
Factory Farms: 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." 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."