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. 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 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 . The most common foodborne pathogens 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 include Salmonella, Campylobacter and Listeria monocytogenes. Salmonella is the organism responsible for the greatest number of hospitalizations and deaths 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 from foodborne illness than any other food. A 2014 survey 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. 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 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 (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 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 (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 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 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 about overflowing lagoons of pig waste after Hurricane Florence illustrates how animal waste can unintentionally spread. Contamination of produce 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 views antimicrobial resistance as a “fundamental threat to human health.” The CDC estimates 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. 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. Antibiotics are also given to prevent two diseases 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.
In cattle, antibiotics are routinely given throughout a cow’s life to treat illness, prevent illness and promote growth. 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 are the same as those used in human medicine. In cattle, for example, these include ampicillin, amoxicillin, penicillin, erythromycin, tetracycline and sulfa drugs.
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. 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 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 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.
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 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, “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 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. 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. Another avian influenza virus, H7N9, has infected over 1500 people with a mortality rate of 40 percent. According to the World Health Organization: “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.
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.
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Impact of animal agriculture on the planet & benefits of a plant-based diet:
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Animal agriculture and foodborne illness:
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8. Centers for Disease Control and Prevention. Estimates of Foodborne Illness in the United States.
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Antibiotic overuse and the rise of resistant bacteria:
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