Food systems impact three important facets of health: personal health, the health of our planet, and public health (Figure 1). The individual health benefits of a plant-based diet and the catastrophic environmental and biodiversity impact of animal agriculture are well documented(opens in a new tab). But the serious threats to public health posed by the industrial-scale propagation and slaughter of domestic animals for food deserve wider attention — from the genesis of foodborne illnesses and development of antibiotic-resistant bacteria to the creation of reservoirs for human viral pandemics.
Foodborne illness is a major public health problem
The CDC estimates(opens in a new tab) that each year about 48 million people in the U.S. get sick, and 3,000 die, from consuming contaminated food. Contaminated beef, pork and poultry are responsible for 40 percent of all (opens in a new tab). The most common foodborne pathogens (opens in a new tab)are norovirus and four kinds of bacteria: Salmonella, Clostridium perfringens, Campylobacter and Staphylococcus aureus. The pathogens that are most likely to be found in slaughtered livestock and poultry(opens in a new tab) include Salmonella, Campylobacter and Listeria monocytogenes. Salmonella is the organism responsible for the greatest number of hospitalizations and deaths(opens in a new tab) from contaminated food.
Cows in feedlot and bacteria micrograph.
Bacterial contamination of meat and poultry: the rule, not the exception
According to the CDC, poultry products are responsible for more human deaths(opens in a new tab) from foodborne illness than any other food. A 2014 survey(opens in a new tab) of over 300 retail chicken breast samples carried out by Consumer Reports found that 97 percent of the chicken breasts harbored human pathogens, including Salmonella and E. coli. Almost half of the samples contained one or more multiple-antibiotic-resistant bacteria. Even chicken labeled “organic” or “no antibiotics” contained antibiotic-resistant human pathogens. And more than half of the chicken breasts tested were tainted with fecal matter.
It should be no surprise that retail chicken is so highly contaminated, considering the way most chickens are raised and slaughtered. Factory-farmed chickens live in cramped, filthy conditions where the breakdown of their feces leads to high levels of toxic ammonia in the air(opens in a new tab). After essentially living in their feces, chickens are transported for slaughter in wire cages stacked on top of each other, where even more feces and fecal pathogens spread onto their skin and feathers. Inevitably, when the chickens are slaughtered, that fecal matter with its associated gut pathogens (including Salmonella) comes in contact with the chicken meat.
A 2013 Consumer Reports survey(opens in a new tab) of retail pork chops and ground pork found that almost 70 percent of pork samples tested positive for Yersinia enterocolitica, a pathogenic species of bacteria that causes gastroenteritis(opens in a new tab) (gastrointestinal infection), especially in young children. Other common food pathogens, including Listeria monocytogenes, Staphylococcus aureus and Salmonella, were also detected, as was Enterococcus, a marker of fecal contamination. Over 90 percent of the pathogenic bacteria isolated from the pork samples were resistant to one or more antibiotics.
A 2015 Consumer Reports investigation(opens in a new tab) found that 100 percent(300 of 300 samples) of ground beef sold in supermarkets and natural foods stores in the U.S. was contaminated with fecal bacteria. 14 percent of the tested samples contained multiple-antibiotic-resistant “superbugs.” Ground beef is the most commonly identified source of infections by Shiga toxin-producing (opens in a new tab)(including E. coli O157), which causes illness in 200 people every day in the U.S. and can cause severe illness and death. E. coli O157 lives in the guts(opens in a new tab) of apparently healthy ruminant animals, and is readily transferred to their carcasses when they are slaughtered.
Even the outbreaks of foodborne pathogens that are traced to fresh produce, such as lettuce or spinach, commonly originate from farm animal waste, in which fecal pathogens can survive for months. Contamination with bacterial pathogens(opens in a new tab) can come from the application of raw or poorly composted manure to fields, or exposure of crops to contaminated waste via irrigation or accidental flooding. A recent New York Times(opens in a new tab) about overflowing lagoons of pig waste after Hurricane Florence illustrates how animal waste can unintentionally spread. Contamination of produce(opens in a new tab) can occur if trucks aren’t cleaned after transporting animals or animal products, or through contact with animal products in the kitchen.
Pigs transported by truck and pig waste slurry.
The overuse of antibiotics in animal agriculture
The World Health Organization(opens in a new tab) views antimicrobial resistance as a “fundamental threat to human health.” The CDC estimates(opens in a new tab) that every year, more than 400,000 people in the U.S. are sickened with antibiotic-resistant Salmonella or Campylobacter. When bacterial pathogens develop resistance to multiple antibiotics, it becomes increasingly difficult and expensive to effectively treat the diseases they cause in people.
The rise of multiple-antibiotic-resistant bacteria can be attributed to antibiotic overuse in people and in farm animals. In poultry, antibiotics are used to both treat and prevent diseases(opens in a new tab). For example, the high levels of ammonia in chicken houses damage eye and lung tissue and lead to infection, especially with E.coli, requiring antibiotic treatment(opens in a new tab). Antibiotics are also given to prevent two diseases(opens in a new tab) that are common in chickens: coccidiosis (a protozoal disease) and necrotic enteritis (caused by the bacteria Clostridium). Historically, antibiotics have also been given to chickens (along with arsenic, until 2015) to promote rapid growth(opens in a new tab).
In cattle, antibiotics are routinely given throughout a cow’s life to treat illness, prevent illness and promote growth(opens in a new tab). The period when calves are separated from their mothers is a time of great stress. The strain of early separation, sometimes along with variable weather conditions, can make calves vulnerable to pneumonia. Antibiotics are often given at this stage both to prevent pneumonia and to help sick cattle recover. Prophylactic antibiotics are also commonly fed to calves as they approach their final weight before slaughter. At that stage in their abbreviated lives, due to the high percentage of grain in their diet, calves are prone to develop abscesses (pockets of infection) in their livers. Low levels of antibiotics in feed are also often used just to promote growth, and various antibiotics are used as needed to treat conditions such as pink eye and infected wounds.
About half of the antibiotics used in animal agriculture(opens in a new tab) are the same as those used in human medicine. In cattle, for example, these include ampicillin, amoxicillin, penicillin, erythromycin, tetracycline and sulfa drugs(opens in a new tab).
Bacteria are not the only animal-transmitted pathogens of concern
Pigs are a source of many parasitic protozoa and worms that can infect and cause disease in humans(opens in a new tab). One parasite of significant health concern is Toxoplasma gondii, which causes the disease toxoplasmosis. According to the CDC, this parasite is the second leading cause of death (opens in a new tab)from foodborne illness in the U.S. Pregnant women and immunocompromised individuals are particularly vulnerable. In the U.S., an estimated 500–5,000 cases of congenital toxoplasmosis(opens in a new tab) occur each year, transmitted from infected mother to fetus. While many people think of toxoplasmosis as a disease contracted only from cat litter, undercooked or raw meats, including pork and lamb, are a significant source of infection(opens in a new tab).
Chicken CAFO and influenza micrograph.
Viral transmission from animals to humans
The loss of millions of domestic pigs in Asia in the past year due to the African swine fever virus vividly illustrates how rapidly disease can spread(opens in a new tab) in domestic animal populations. While the African swine fever virus does not infect humans, the same is not true of the influenza viruses that infect animals. According to the CDC(opens in a new tab), “Flu viruses are constantly changing and animal flu viruses can change such that they may gain ability to infect people easily and spread among people, causing a pandemic.” The 2009 swine flu pandemic is one such example. The H1N1 swine influenza virus(opens in a new tab) spread to 74 countries and killed over 200,000 people worldwide in one year. H1N1 was a new variant virus that contained genes from swine, avian and human flu viruses. Pigs can be infected by influenza viruses from birds, humans and pigs; in fact, seasonal human flu viruses are commonly transmitted to pigs. Pigs provide an environment rife for genetic recombination among different strains of influenza, and are a breeding ground for new potentially deadly strains of flu.
Avian influenza H5N1, one of the most deadly viruses known to infect humans, occurs mainly in poultry and wild birds, but human infections have been reported throughout the world(opens in a new tab). The first human outbreaks occurred in 1997, and since then, avian influenza H5N1 has infected over 700 people with a mortality rate of close to 60 percent(opens in a new tab). Another avian influenza virus, H7N9, has infected over 1500 people with a mortality rate of 40 percent(opens in a new tab). According to the World Health Organization(opens in a new tab): “Ongoing circulation of some avian influenza viruses in poultry, such as A(H5) and A(H7) viruses, are of public health concern as these viruses cause severe disease in humans and the viruses have the potential to mutate to increase transmissibility among humans.” The CDC takes the threat of a human pandemic from avian influenza so seriously that it is stockpiling the Asian influenza H5N1 vaccine(opens in a new tab).
The positive public health impact of choosing plant-based
Raising animals for food is responsible for millions of cases of food poisoning each year in the U.S., contributes to the rise of multiple-antibiotic-resistant human pathogens, and serves as a breeding ground and incubator for the next deadly human influenza pandemic. Every time you choose the Impossible Burger instead of a burger made from a cow, or Impossible Sausage Made from Plants instead of a sausage patty made from a pig, you’re making a good choice not only for your own health and the health of our planet, but for global public health.
Questions, comments or thoughts? We welcome constructive conversation. Reach out to us at [email protected](opens in a new tab).
Impact of animal agriculture on the planet & benefits of a plant-based diet:
1. Brown, Pat, The Mission that Motivates Us(opens in a new tab), Medium.com. January 23, 2018
2. Clark, M., Springmann, M., Hill, J. and Tilman, D. Multiple health and environmental impacts of food.(opens in a new tab) Proc Natl Acad Sci USA. 2019 Nov 12; 116(46):23357.
3. Springmann, M., et al. Health and nutritional aspects of sustainable diet strategies and their association with environmental impacts: a global modelling analysis with country-level detail(opens in a new tab) Lancet Plant Health. 2018 Oct; 2(10):e452.
4. Springmann, M., Godfrey, H., Rayner, M. and Scarborough, P. Analysis and valuation of the health and climate change cobenefits of dietary change(opens in a new tab). Proc Natl Acad Sci USA. 2016 April 12; 113(15):4146.
5. Satija, A. and Hu, F. Plant-based diets and cardiovascular health(opens in a new tab). Trends Cardiovasc Med. 2018 Oct; 28(7): 437.
6. Machovina, B., Feeley, K. and Ripple, W. Biodiversity conservation: the key is reducing meat consumption(opens in a new tab) Science of the Total Environment 2015; 536:419.
Animal agriculture and foodborne illness:
7. PEW Charitable Trust Report. Emerging Pathogens in Meat and Poultry(opens in a new tab) 2016.
8. Centers for Disease Control and Prevention. Estimates of Foodborne Illness in the United States(opens in a new tab).
9. Painter, J., et al., Attribution of Foodborne Illnesses, Hospitalizations, and Deaths to Food Commodities by using Outbreak Data, United States, 1998–2008(opens in a new tab). Emerg Infect Dis. 2013 Mar; 19(3): 407.
10. Food and Drug Administration. Bad Bug Book (Second Edition(opens in a new tab). 2012.
11. Heiman, K., et.al., Escherichia coli O157 Outbreaks in the United States, 2003–2012(opens in a new tab). Emerg Infect Dis. 2015 Aug; 21(8): 1293.
12. Cooley, M., et.al., Incidence and Tracking of Escherichia coli O157:H7 in a Major Produce Production Region in California(opens in a new tab). PLoS ONE 2(11): e1159.
13. Centers for Disease Control and Prevention. How Food Gets Contaminated — The Food Production Chain(opens in a new tab).
14. Centers for Disease Control and Prevention. CDC and Food Safety(opens in a new tab).
15. Centers for Disease Control and Prevention. Preventing Congenital Toxoplasmosis(opens in a new tab). MMWR 2000 Mar; 49(RR02):57.
17. Aziz, T. and Barnes, H., Harmful Effects of Ammonia on Birds(opens in a new tab), Poultry World, October 2010.
18. Rock, A. How safe is your ground beef?(opens in a new tab) Consumer Reports, December 2015.
19. Pork chops and ground pork contaminated with bacteria: We found antibiotic-resistant bacteria and traces of a veterinary drug(opens in a new tab). Consumer Reports, January 2013.
20. Pierre-Louis, K., Lagoons of pig waste are overflowing after Florence. Yes. That’s as nasty as it sounds(opens in a new tab). The New York Times, September 18, 2018.
21. United States Department of Agriculture. FSIS(opens in a new tab), August 26, 1999.
Antibiotic overuse and the rise of resistant bacteria:
22. United Nations Press Release: High Level Meeting on Antimicrobial Resistance(opens in a new tab). September 21, 2016.
23. Twilley, N., Graber, C and Gastropod. How the Chicken Industry Got Hooked on Antibiotics(opens in a new tab). The Atlantic, August 16, 2017.
24. National Chicken Council. Questions and Answers about Antibiotics in Chicken Production(opens in a new tab), February 8, 2019.
25. Beef 2 Live. Antibiotics in Cattle(opens in a new tab). South Dakota University, January 26, 2020.
26. Virginia Cooperative Extension, Table 1. Injectable Antibiotics Approved for Use in Beef Cattle(opens in a new tab).
27. Food and Agriculture Organization of the United Nations, One year on, close to 5 million pigs lost to Asia’s swine fever outbreak(opens in a new tab). August 9, 2019.
28. Centers for Disease Control and Prevention. Highly Pathogenic Asian Avian Influenza A(H5N1) Virus(opens in a new tab).
29. Centers for Disease Control and Prevention. What People Who Raise Pigs Need to Know About Influenza (Flu)(opens in a new tab).
30. World Health Organization. Influenza (Avian and other zoonotic(opens in a new tab). November 13, 2018.
31. Kain, T. and Fowler, R. Preparing intensive care for the next pandemic influenza(opens in a new tab). Critical Care. 2019; 23:337.