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.

Notes

[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: http://www.washingtonpost.com/wp-dyn/content/article/2009/04/28/AR2009042804041.html?hpid=topnews&sid=ST2009042900988

[4] The World Health Report 2007, “A safer future: Global public health security in the 21^st century” (2007). Available at: www.who.int/entity/whr/2007/whr07_en.pdf

[5] USDA, “Livestock slaughter 2003 summary.” Available at: http://usda.mannlib.cornell.edu/usda/nass/LiveSlauSu//2000s/2004/LiveSlauSu-05-04-2004.txt; USDA, “Poultry slaughter 2003 annual summary,” (2004). Available at: http://usda.mannlib.cornell.edu/usda/nass/PoulSlauSu//2000s/2004/PoulSlauSu-03-08-2004.txt.

[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: www.msnbc.msn.com/id/30398682/this 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: www.apha.org/advocacy/policy/policysearch/default.htm?id_1243

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The simple answer is that vaccine policy in the United States is riddled with inconsistencies that discriminate against those coming into the country.

On September 30, 1996, Congress amended the Immigration and Nationality Act, or INA, by adding the requirement that all immigrants prove receipt of all vaccinations recommended by the Advisory Committee on Immunization Practices.[3] Thus, vaccines that are only recommended to the U.S. population automatically became mandatory for immigrants. Many of the ACIP-recommended vaccines are actually mandated for children entering public schools, but parents can home-school their children if they prefer not to vaccinate. With the exception of girls in Virginia’s public schools, Gardasil is not required for any female in the United States, public school-educated or not. This left many immigration advocates asking why immigrant girls and women should be required to have a vaccine that’s not required of most U.S. citizens.

Should the government mandate those vaccines targeted against diseases that do not pose immediate public health threats?

A 1990 amendment to the INA authorized for the exclusion of immigrants officials felt have “communicable diseases of public health significance.”[4] It is reasonable to infer that this amendment was intended to protect the U.S. population from exposure to serious infectious diseases carried by immigrants entering the country, and that the later vaccination requirements were intended for the same reason. Yet these requirements don’t apply to all who enter the country. Refugees residing in the U.S. are exempt from the vaccination requirements (unless and until they apply for adjustment of status for permanent residence), as are temporary visitors.[5] If the purpose of the law is indeed to protect the U.S. population against infectious diseases, then it would follow that all visitors entering the country must be vaccinated, since any could be a potential carrier of vaccine-preventable contagious diseases.

Another glitch in this policy, if it is designed to protect against broad threats to public health, is that not all vaccine-preventable diseases are actually contagious. The toxin produced by the bacterium Clostridium tetani causes tetanus, and the tetanus vaccine is very effective at protecting against the development of this lethal disease. It is understandable that the vaccine is recommended by the ACIP, yet by default the vaccine is mandatory for all immigrants. However, tetanus is not spread from person to person. Why is this vaccine mandated for immigrants when it doesn’t confer any protection to the population at large, but only to the individual receiving the vaccine?

While HPV is transmissible from person to person, the cervical cancer that can result from HPV infection does not usually manifest until years or even decades after. HPV does not pose an immediate significant threat to the population, unless we decide to define genital ulcers as significant threats. Pharmaceutical companies are researching other vaccines like Gardasil intended to protect against diseases that manifest years or decades after infection. This is in contrast to traditional vaccines targeted against highly contagious diseases spread via the respiratory route, which do pose immediate threats to the population. Should the government mandate those vaccines targeted against diseases that do not pose immediate public health threats?

One could argue that the immigration vaccine policy is an economic protection because the financial burden for the treatment for tetanus, cancers, and other such diseases might be significant; thus it’s better to prevent them to reduce healthcare costs. One could also argue that the vaccines should be administered to immigrants for their own, individual benefit. But again, there is an inconsistency. If these are in fact the reasons behind the vaccine requirement for immigrants, then logically, the vaccines should be mandatory for U.S citizens, too.

Ultimately, the different rules for immigrants are a question of justice. The policy places a burden on immigrants that is not demanded of U.S. citizens. Vaccines are expensive. Gardasil, administered in three doses, costs about $360 for the series.[6] The high cost is a disadvantage to poorer immigrants. A physician may waive the vaccine requirements if there are medical contraindications, such as an allergy to the vaccine. An immigrant may also opt out of vaccines on the basis of religious or moral objections, but he or she must be opposed to vaccinations in all forms.[7] Immigrants are often desperate to enter the United States, and if there is any perception that opposition to vaccination could be used to deny them entry, it is unlikely they will protest such preconditions.

Unlike immigrants, U.S. citizens are allowed to cherry pick what vaccines, if any, they receive. While there is a set of mandatory vaccinations for children entering public school, parents can simply choose home schooling. Many adult vaccines, such as herpes zoster vaccines, are completely optional. If a young U.S. woman opposes the vaccine Gardasil on the grounds that she is not sexually active, she can do so without having to forgo other vaccines. Immigrant females do not have this choice. They must either take all or no vaccinations. This lack of choice leaves them in a precarious and vulnerable situation—in terms of health and cultural discrimination. Immigrants are already vulnerable to stigma due to language barriers, differences in appearance, and cultural practices. Mandatory vaccination of immigrants can compound negative views towards them by implying that they are sexually promiscuous, disease-ridden, and pose significant health risks to Americans.

The immigration vaccine policy should be rooted in sound scientific and public health rationales. As it stands, it is discriminatory and it can compound a sometimes-hostile environment toward immigrants. Moreover, the current inconsistencies of the immigration-related policy could undermine all vaccine-related policies and guidelines. A growing group of U.S. parents are opting out of vaccinating their children because of a lack of trust in the decision-making behind the vaccination guidelines. Misinformation in the media about an unsubstantiated link between vaccines and autism has fueled the anti-vaccine movement, though recent findings and a court ruling last month underscore the fact the opposition rests on little to no evidence.[8] Inconsistencies in vaccine policy for immigrants undermine the entire system. Moreover, continued opposition to vaccination could lead to a resurgence of very serious and immediately threatening diseases that have been largely absent in recent U.S. history, as exemplified by a recent Haemophilus influenzae type B (Hib) meningitis outbreak in Minnesota among five children, three of whose parents had opted not to have them vaccinated.[9] Further discussion of immigrant vaccination policy must involve what constitutes a significant public health threat, what is equitable, and what is reasonable given economic and political constraints. At the very least, however, the policy needs to be fair, effective, and re-evaluated.

Aysha Akhtar, MD, MPH a neurologist and public health specialist and a fellow of the Oxford Centre for Animal Ethics. She can be reached at: aysha.akhtar@oxfordanimalethics.com.

Notes

[1] Markowitz LE, Dunne EF, Saraiya M, Lawson HW, Chesson H, Unger ER, Centers for Disease Control and Prevention, Advisory Committee on Immunization Practices (ACIP), “Quadrivalent Human Papillomavirus Vaccine: Recommendations of the Advisory Committee on Immunization Practices (ACIP),” MMWR Recomm Rep. 2007, 56(RR-2):1-24.

[2] “Merck lobbies for vaccine policy to become law,” Associated Press, January 30, 2007, available  at: http://www.foxnews.com/story/0,2933,248781,00.html (last accessed February 22, 2009).

[3] Mautino KS, “Vaccination requirements for immigrants to the United States,” Journal of Immigrant Health, 1999 (1): 61-63.

[4] Ibid.

[5] Ibid; CDC, “Adjustment of status for U.S permanent residence requirements: technical instructions for vaccination 2008,” available  at: http://www.cdc.gov/Ncidod/dq/civil.htm (last accessed January 12, 2009).

[6] Mary Engle, “Immigrant advocates decry cervical cancer vaccine order,” Los Angeles Times, October 22, 2008, available at: http://articles.latimes.com/2008/oct/22/science/sci-gardasil22 (last accessed January 20, 2009).

[7] U.S. Department of Justice Immigration and Naturalization Service, “Medical examinations, vaccination requirements, waivers of medical grounds of inadmissibility, and Designation of civil surgeons and revocation of such designation” (AD 01-03), October 17, 2002, available at: http://www.immigrationequality.org/uploadedfiles/2002%20HIV%20Immigration%20policy%20memo.pdf (last accessed January 20, 2009).

[8] WebMD, “Vaccine court rejects autism claim,” February 12, 2009, available at: http://www.webmd.com/brain/autism/news/20090212/vaccine-court-rejects-autism-claims (last accessed February 22, 2009).

[9] WebMD, “Hib outbreak kills unvaccinated child,” available at: http://children.webmd.com/vaccines/news/20090123/hib-outbreak-kills-unvaccinated-child (last accessed February 6, 2009).

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