By Michael Greger, Special to CNN



Editor’s note: Michael Greger is the director of public health and animal agriculture at The Humane Society of the United States, and author of ‘Bird Flu: A Virus of Our Own Hatching.’ The views expressed are his own.

In 1969, U.S. Surgeon General Dr. William Stewart declared “The war against diseases has been won.” We had penicillin. We had conquered polio and smallpox. Even Nobel laureates were seduced into the heady optimism. To write about infectious disease, one Nobel-winning virologist wrote in a 1962 textbook, “is almost to write of something that has passed into history.” “[T]he most likely forecast about the future of infectious disease,” he pronounced, “is that it will be very dull.” Recent headlines belie the fact that it has become anything but – from the mysterious SARS-like virus discovered in London, to Hantavirus in Yosemite and plague in Colorado to West Nile virus in Texas and the new Heartland virus in Missouri.

We've seen an unprecedented rise in infectious diseases in recent decades, 75 percent of which are “zoonotic,” meaning they come from animals. About 300 new animal-to-human diseases have emerged in the last 60 years.

This summer, the International Livestock Research Institute released a report estimating that zoonotic diseases cause 2.5 billion cases of human illness each year and 2.7 million human deaths worldwide. Most of these illnesses and deaths are caused by diseases spread from farm animals.

Meanwhile, we’ve seen a dramatic spike in pork and poultry production. Tens to hundreds of thousands of caged animals under a single roof allow for zoonotic diseases to emerge, amplify and spread. Of all the emerging threats, the greatest concern is influenza, the only known virus with the potential to infect millions of people within months.

New chicken and pig flu viruses have emerged at an alarming rate in recent decades. The latest swine flu virus, dubbed H3N2v, claimed its first human victim last month in Ohio. Up until the 1990s, only about a dozen human cases of swine flu infection had ever been reported. In the last year alone, in contrast, H3N2v has infected 300 people, sending 15 to the hospital and one to the morgue. The H1N1 virus that emerged from pigs in 2009 infected an estimated 60 million Americans, resulting in 12,000 deaths, according to the Centers for Disease Control and Prevention.

Both H3N2v and the pandemic H1N1 share genetic origins with the “triple reassortant” strain that spread throughout the U.S. pork industry in 1999, a virus that combined genes from bird, pig, and human strains. Our first discovered hybrid strain – a human-pig mutant – was found in August 1998 in an industrial pig operation in Newton Grove, N.C. It may be no coincidence that the new strain was found in a region with the single highest pig population in the nation, or that it was found in a “sow stall” operation, in which thousands of pregnant sows were confined in crates barely larger than their bodies. (The stress of life-long confinement is thought to make animals more susceptible to infection).

Bird flu followed a similar trajectory, from rare cases to a multitude of new chicken flu viruses now causing sporadic human outbreaks around the world. The greatest concern is that with increasing numbers of circulating pig and chicken flu viruses capable of infecting humans, a virus with the human transmissibility of H1N1 could combine with a virus with the human lethality of H5N1, a bird flu virus that has killed 359 of its 608 known human victims. Imagine the implications of 60 million Americans coming down with flu with a 60 percent mortality rate.

While budget strapped public health agencies struggle to detect and prevent emerging strains, and researchers work on unlocking genetic codes, the pork industry specifically has a vital role to play in preventing a human pandemic, and it begins with transparency and better animal welfare. Animal health regulations only require producers to notify authorities of pathogens that pose a risk to the national herd, such as hoof and mouth disease. But those regulations were put in place before we realized that swine flu viruses could pose a risk to the national human population. Yet producers still don't have to share the results of their swine flu testing programs with health agencies. Even if a person is infected on a farm, health authorities are barred from testing pigs without express consent from the owner of the operation. Especially in light of the hundreds of new human cases, the U.S. pork industry can no longer be allowed to simply self-regulate and keep public health authorities in the dark.

For years, the public health community has warned about the risks of intensive livestock confinement. In 2003, the American Public Health Association called for a moratorium on concentrated animal feeding operations. In 2008, the Pew Commission on Industrial Farm Animal Production, which included a former U.S. Secretary of Agriculture, concluded that industrialized animal agriculture posed “unacceptable" risks to public health. A key recommendation was the phasing out of extreme confinement practices such as gestation crates, which “induce high levels of stress in the animals and threaten their health,” the commissioners wrote, “which in turn may threaten human health."

In response, the pork industry appeared more interested in changing the name of swine flu than in changing the practices that are exacerbating it. An editorial in one leading U.S. agribusiness publication responded this way to a United Nations report on the human health risks of industrialized animal agriculture: “FAO [Food and Agriculture Organization of the United Nations] claims to use scientists to generate its reports, but I wonder if those scientists don’t resemble a bearded man living in a cave in Pakistan who wants the U.S. on its knees.”

Rather than shooting the messenger, it would be more prudent to allow the public health community’s concerns to inform agriculture policy, and for test results to be shared to eliminate the most extreme forms of animal confinement.