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Flu Farms?

Decreasing Factory Farming Could Help Avert the Next Epidemic

pigs in a holding pen SOURCE: AP/Alexandre Meneghini Controlling infections once they reach the human population is crucial, but the origin of many pathogens may lie in factory farming operations, where potent diseases develop.

As the number of confirmed cases of swine flu around the globe increases, we grow closer and closer to having a pandemic on our hands. In preparation against that possibility, governments are emphasizing prevention of further human-to-human transmission and treatment for those who are ill. Talk about greater distribution of filter masks, vaccine production, and limitations on international travel abounds. Surprisingly, however, there is very little discussion about how swine flu got started in the first place.

The primary reservoir for influenza viruses is aquatic birds, but humans are not readily directly infected by the strains from those animals.[1] Pigs, however, are highly susceptible to both avian and human influenza A viruses. They are commonly referred to as “mixing vessels” in which avian and human viruses commingle. In pigs, viruses swap genes, and new influenza strains emerge with the potential to infect humans. Pigs may have been the intermediate hosts responsible for the birth of the last two flu pandemics in 1957 and 1968 and the current swine influenza A, called H1N1, is a triple hybrid avian/pig/human virus.[2]

In order to better avert the threat of epidemics like the one currently spreading around the globe, public health efforts must address the conditions that allow pigs to become breeding grounds for infectious disease. More focus needs to be placed on preventing pathogens from getting into the human population in the first place, and that means starting at the farm. The source of the current epidemic has not yet been identified, but the first confirmed case of swine flu occurred in La Gloria, Mexico, a town surrounded by industrial pig farms, partly owned by Smithfields Foods.[3] We should note of course that the Centers for Disease Control and Prevention have made it clear that consumers cannot get swine flu from eating pork or pork products. But even if these particular farms are not confirmed as the primary source, based on research into the previous outbreaks of swine flu, it makes sense to consider factory farms as very likely potential sites for the development of these pathogens.

For centuries, the evolution of the flu virus has remained relatively stable. However, in recent years the influenza virus has undergone an “evolutionary surge,” with new variants emerging rapidly. But this is not limited to influenza. According to the World Health Organization, we are seeing more new infectious diseases and epidemics than ever before, and they are appearing at an alarming rate.[4] What could be causing such a surge in new infections? Increased human travel is certainly a factor, but perhaps the most significant variable is the change in animal agricultural practices that have occurred in the last few decades.

Global demand for meat has increased substantially in recent years. In the U.S. alone, approximately 1 million land animals are slaughtered for food every hour.[5] By 2020, world meat production is expected to double.[6] As a result of the rise in animal product demand, traditional farming practices have been mostly replaced in developed countries by immense intensive animal operations, and developing countries are rapidly catching up.

Increasingly, thousands of animals are confined in these operations, often crowded into sheds. The percentage of operations in North America with 5,000 or more animals expanded from 18 percent in 1993 to 53 percent in 2002.[7] The crowding leads to stressful and profoundly unhygienic conditions. Animals continuously inhale and recirculate aerosolized fecal matter, methane, and ammonia. The wastes and fumes emanating from these intensive operations are so concentrated that nearby human communities commonly have substantial increases in respiratory illnesses such as asthma.[8] The combination of reduced immunity due to prolonged stress in the pigs and the high-density confinement render these operations perfect breeding grounds for new pathogens. Under these conditions, new strains of swine flu are rapidly generated and transmitted from one pig to another by the respiratory route.

In 1988, 2,400 pigs in a North Carolina operation were sickened by a strain of swine flu not seen before.[9] Since that time numerous new flu viruses have emerged and have swept across pig operations throughout North America. WHO and other organizations cite intensive pig farming and other animal factory operations as a significant contributing factor to zoonotic pathogens.[10] Because of the high infectious disease rates in these operations, farm animals are given a constant influx of antibiotics; half of all U.S. antibiotics are given to farm animals.[11] This inundation of medicine helps select for drug-resistant bacteria, which in turn could be transmitted to humans. In addition, vaccination for farm animals is now common. It is routine to vaccinate pigs against swine flu, but rather then ameliorating the problem, vaccinations may actually exacerbate the problem by selecting for new, vaccine-resistant viruses.[12] Vaccinating farm animals may not be an effective preventive measure.

Our high demand for animal products has trapped us in a never-ending cycle. To meet the demand economically, animals are placed into high-density confinement, which sickens them; they are given antibiotics and vaccines to prevent this, which in turn produces more virulent or drug-resistant pathogens. So how do we stop this?

The answer, according to many governments, is to control the spread of infection once it spreads to the human population with physical barriers, vaccination, and medication. This is certainly necessary, but it is not the whole solution. Because new influenza strains are popping up continuously, it is difficult to anticipate the next serious strain that warrants a vaccine. There can be a long lag time between an outbreak and the availability of an appropriate vaccine. Vaccines also might not confer total protection to all citizens, and although generally safe, might, on rare occasions, have unintended consequences, as was the case with the swine flu outbreak at Fort Dix, New Jersey in 1976, in which the influenza vaccine was associated with increased cases of Guillain-Barré disease, a neurological illness of acute paralysis.[13] Moreover, antivirals and antibiotics are becoming ineffective because of the development of new, resistant strains. The current swine flu is resistant to two out of four potential antiviral medicines.[14]

The high-density intensive animal operations need to go. Not only are they hotbeds for pathogens, but they are also environmentally unsustainable and cruel to the animals involved. The American Public Health Association, recognizing the adverse public health consequences of these intensive farms, has called for a moratorium.[15] That’s a great step in the right direction, but it is not enough. To reduce the supply, the demand for animal products must decrease.

With one exception thus far, the current swine flu cases outside of Mexico appear to be relatively mild in severity and the outbreaks may fizzle out. Even if it does, however, genes between different flu strains are being swapped and re-assorted in pig farms across the world. The next major pandemic is just a matter of time. If we learn anything from the current outbreaks, it is that we can’t afford to wait for the next one. We need to address the root of the problem: the intensive farm animal operations and our own appetites.

Aysha Akhtar MD, MPH is a fellow for the Oxford Center for Animal Ethics and a neurologist and public health specialist at the Food and Drug Administration.

The opinions expressed here are those of the author and do not represent the official position of the U.S. Food and Drug Administration or the U.S. government.


[1] Webby RJ, Rossow K, Erickson G, Sims Y, Webster R, “Multiple lineages of antigenically and genetically diverse influenza A virus co-circulate in the United States swine population,” Virus Research (2004) 103: 67-73.

[2] Wuetrich B., “Chasing the fickle swine flu,” Science (2003) 299:1502-1505.

[3] The Washington Post, “Little boy at the center of a viral storm,” April 29, 2009. Available at:

[4] The World Health Report 2007, “A safer future: Global public health security in the 21st century” (2007). Available at:

[5] USDA, “Livestock slaughter 2003 summary.” Available at:; USDA, “Poultry slaughter 2003 annual summary,” (2004). Available at:

[6] Pearson J, Salman MD, BenJabara K, et al. “Global risks of infectious animal diseases,” Council for Agricultural Science and Technology, Issue Paper No. 28. (2005).

[7] Wuetrich, “Chasing the fickle swine flu.”

[8] Mirabelli MC, Wing S, Marshall SW, Wilcosky TC, “Asthma symptoms among adolescents who attend public schools that are located near confined swine feeding operations,” Pediatrics (2006) 118:e66 –75; Wing S, Wolf S., “Intensive livestock operations, health and quality of life among Eastern North Carolina residents,” Environ Health Perspect. (2000) 108:233–8; Merchant JA, Naleway AL, Svendsen ER, et al., “Asthma and farm exposures in a cohort of rural Iowa children,” Environ Health Perspect. (2005) 113:350–6.

[9] Wuetrich, “Chasing the fickle swine flu.”

[10] Wuetrich, “Chasing the fickle swine flu”; Washington Post, “Little boy at the center of a viral storm”; Pearson J, Salman MD, BenJabara K, et al., “Global risks of infectious animal diseases.”

[11] “Antimicrobial resistance: issues and options,” In: Harrison PF, Lederberg J, eds., “Forum on emerging infections,” Institute of Medicine, (Washington DC: National Academy Press, 1998); “Putting meat on the table: industrial farm animal production in America,” The Pew Charitable Trusts and Johns Hopkins Bloomberg School of Public Health, a report of the Pew Commission on industrial farm animal production (2008).

[12] Wuetrich, “Chasing the fickle swine flu.”

[13] Sencer DJ, Millar JD, “Reflections on the 1976 swine flu vaccination program,” Emerging Infectious Diseases (2006) 12: 29-33.

[14] Associated Press, “Global race is to contain swine flu outbreak,” April 27, 2009. Available at: strain of A/H1N1 swine flu

[15] American Public Health Association, “Precautionary moratorium on new concentrated animal feed operations,” APHA policy statement number 20037 (2003). Available at:


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