Livestock farming has undergone a significant transformation in the past few decades. Most meat and dairy products now are produced on large farms with sin-gle species buildings or open-air pens. Breeding programs have focused on production, getting more food produced in less time and for less cost per unit. Since 1960 milk production has more than doubled, meat production has more than tripled, and egg production has more than quadrupled. It now takes far less time to raise fully grown animals. In 1920, for instance, a chicken took approximately 16 weeks to reach a little over 2 pounds. Now they can reach 5 pounds in 7 weeks!
These new technologies have allowed farmers to continually reduce per unit costs, which means bigger profits on less land and capital, which results in further incentive to increase farm size.
“Factory farms”, those that use these confinement approaches and scale up, are often criticized for the smell and water pollution caused by the resulting vol-ume of manure; the unhealthy, grain-heavy diets ruminants consume there; and the stressful, crowded conditions in which the animals live.
Johns Hopkins researchers Ellen Silbergeld, Jay Graham, and Lance Price write: “Concentrated animal feeding operations (CAFOs) are comparable to poorly run hospitals, where everyone is given antibiotics, patients lie in unchanged beds, hygiene is nonexistent, infections and re-infections are rife, waste is thrown out the window, and visitors enter and leave at will.”
By concentrating large numbers of animals together, factory farms are powerful incubators for disease. The stress of life under factory farm conditions weakens an animal’s immune system; ammonia from accumulated waste burns the lungs and makes them more susceptible to infection; the lack of sunlight and fresh air — as well as the identical genetics of industrial farm animal populations — facilitates the spread of pathogens.
These virulent diseases can then spread to the wider community via many routes — not just in food, but also in water, the air, and the bodies of farmers, farm workers, and their families. Once those microbes become widespread in the environment, it’s very difficult to get rid of them. In addition, evidence is emerging of surprisingly high rates of mutation in those disease organisms found in our farm animals.
What are some of the major features of factory farms that make them incubators for disease?
One of the most pressing public health issues associated with factory farms stems from the amount of manure they produce. Large farms can produce more waste than some U.S. cities—a feeding operation with 800,000 pigs can produce over 1.6 million tons of waste a year. That amount is one and a half times more than the annual sanitary waste produced by the city of Philadelphia, Pennsylvania.
It is estimated that livestock animals in the U.S. each year produce as much as 1.2–1.4 billion tons of waste – which is several times more manure than is produced by all the people in the U.S. And remember, though sewage treatment plants are required for human waste, no such treatment facility exists for livestock waste.
While manure is valuable to the farming industry, in large quantities it becomes problematic. Many farms no longer grow their own feed, so they cannot use the manure they produce for fertility. Concentrated operations, especially, must find a way to manage the large quantities of manure produced by their animals. Ground application of untreated manure is one of the most common disposal methods due to its low cost. It has limitations, however, such as the inability to apply manure while the ground is frozen. There are also limits as to how many nutrients from manure a land area can handle.
When manure is applied too frequently or in too large a quantity to an area, nutrients overwhelm the absorptive capacity of the soil, and either run off or are leached into the groundwater. Storage units can break or become faulty, and rainwater can cause holding lagoons to overflow. While confinement op-erations are required to have permits that limit the levels of manure discharge, handling large amounts of manure inevitably causes accidental releases that impact humans.
Manure also contains a variety of potential contaminants. It can contain plant nutrients such as nitrogen and phosphorus, pathogens, growth hormones, antibiotics, animal blood, silage leachate from corn feed, copper sulfate used in footbaths for cows, and chemicals used as additives to minimize the offen-sive smell or other aspects of the manure.
Emissions from degrading manure and livestock digestive processes also produce air pollutants that often affect ambient air quality in communities sur-rounding CAFOs. Greenhouse gases, which contribute to global climate change, are also emitted by confinement operations.
AntibioticsIn the 1950s, American scientists found that adding antibiotics to animal feed increases the growth rate of livestock. Research on this was published and the practice expanded until, in 2001, the Union of Concerned Scientists found that nearly 90% of the total use of antimicrobials in the United States was for non-therapeutic purposes in agricultural production.
Antibiotic-resistant microbes, as well as the antibiotics themselves, are now widely present as environmental contaminants, with unknown consequences for everything from soil microorganisms to people. The U.S. Geological Survey found antimicrobial residues in 48 percent of 139 streams tested nation-wide from 1999 to 2000. Other studies have detected resistant bacteria in the air up to 30 meters upwind and 150 meters downwind of industrial hog facili-ties.
This widespread misuse of antibiotics as feed additives in industrial livestock operations has led, of course, to reduced efficacy of antibiotics in human medicine – a trend that is worrying many medical professionals. The World Health Organization, American Public Health Association, American Medical Association, American Academy of Pediatrics and numerous other public health organizations have called for greater regulation of antibiotic use in livestock.
Biosecurity is broadly defined as any practice or system that prevents the spread of infectious agents from infected to susceptible animals. As poultry and swine production has changed from small-scale methods to industrial-scale operations, there is substantial evidence of pathogen movement between and among these industrial facilities, release to the external environment, and exposure to farm workers, which challenges the assumption that modern poultry production is more biosecure and biocontained as compared with backyard or small holder operations in preventing introduction and release of patho-gens.
Because of the economics of factory farming today, the design and operational requirements of large-scale poultry and swine houses in and of themselves result in compromises of biosecurity. The confinement of thousands of animals requires controls to reduce heat and regulate humidity. Poultry and swine houses are ventilated with high-volume fans that result in considerable bidirectional movement of particles, dust, and biomaterials between the animal house and the external environment. In addition, one study found that as many as 30,000 flies may enter a broiler facility during a single flock rotation in the summer months, suggesting that the impact of insect vectors may also be significant.
Workers in CAFOs and members of nearby communities are also at potential risk of exposure to pathogens. Studies of airborne concentrations of bacteri-al pathogens at CAFOs have found that bacteria were recovered inside and downwind of the facilities at concentrations that could cause a potential human health hazard.
As the human population increases, and mega cities grow, there is greater risk that infectious diseases will evolve, emerge, or spread readily among the populace. The concentration of animals may augment the risk of zoonoses, diseases transmissible from animals to humans. All segments of livestock production might potentially contribute to zoonotic disease, including transportation of livestock, manure handling practices, veterinary medicine, meat processing and animal rendering. Ideally, everyone involved in each of these components of the industry should be cognizant of the infectious disease risks to animals and humans alike, and take precautions. In reality, the economics of factory farming do not currently repay strong efforts to protect workers, neighbors, or the environment.
Many diseases, including the ones listed below whose outbreaks have been widespread on our factory farms, are transferred between livestock and hu-mans. According to some scholars such transfers, combined with other factors, explain major forces in human history. In his 1997 Pulitzer Prize winning book “Guns, Germs, and Steel”, for instance, Jared Diamond introduces the themes he will explore in the following chapters to explain why European peoples have emerged as the dominant group in current history thusly:
“…diverse epidemic diseases of humans evolved in areas with many wild plant and animal species suitable for domestication, partly because the re-sulting crops and livestock helped feed dense societies in which epidemics could maintain themselves, and partly because the diseases evolved from germs of the domestic animals themselves…the availability of domestic plants and animals ultimately explains why empires, literacy, and steel weap-ons developed earliest in Eurasia and later, or not at all, on other continents. The military uses of horses and camels, and the killing power of ani-mal-derived germs, complete the list of major links between food production and conquest that we shall be exploring.”
This bacterial disease is the most common cause of foodborne diarrheal illness (accompanied by nausea, fever and abdominal pain) in the United States, causing an estimated 2 million cases each year. Most don’t require medical treatment, but a small number (approximately 50 per year) end in death. Chicken and turkey are the usual sources: Studies have shown that most conventional chicken is contaminated when it leaves the processing plant. Re-peated studies have concluded that as much as 80 percent of retail supermarket chicken in the United States is contaminated with Campylobacter.
Animal feedstuffs are not thought to be significant source of Campylobacter infection. Instead, it is the environment of the intensive broiler house that is believed to represent the most significant reservoir of infection. Campylobacter strains with identical DNA fingerprints to those colonizing broilers have been measured in air up to 30 meters downwind of broiler facilities housing colonized flocks. Poultry are not the only potential source of Campylobacter, however. In Holland, 85 per cent of pigs sampled were found to be infected with Campylobacter.
This is another bacteria causing frequent and sometimes serious foodborne illness, with an estimated 1.4 million U.S. cases each year, including 18,000 hospi-talizations and 600 deaths. Salmonella can contaminate beef, poultry, eggs and even vegetables. Antibiotic-resistant Salmonella is on the rise: One strain, known as DT104, is resistant to five major antibiotics used in humans.
Before the industrialization of egg production, Salmonella only sickened a few hundred Americans every year and Salmonella Enteritidis was not found in eggs at all. There was a time when our grandparents could drink eggnog and children could eat raw cookie dough without fear of joining the thousands of Americans hospitalized with Salmonella infections every year. By the beginning of the 21st century, however, Salmonella Enteritidis-contaminated eggs were sickening an estimated 182,000 Americans annually.
How is it that Salmonella infection of farm animals is so common, and how is it spread? One way in which Salmonella infection can be introduced and spread is via contaminated feed. But another is specifically tied to conditions in factory farms.
According to scientists at the Central Veterinary Laboratory in the United Kingdom: `Bacterial infections can be spread by the airborne route in farm animals, par-ticularly when reared intensively. For example, poor ventilation in poultry houses can cause high concentrations of ammonia to develop and irritate the respiratory tract, predisposing to infection.”
Salmonella-contaminated battery cage operations in the United States confine an average of more than 100,000 hens in a single shed. As one might expect, such environments can also be significantly contaminated. The massive volume of contaminated airborne fecal dust in such a facility rapidly accelerates the spread of infection. A survey of litter and dust samples from commercial turkeys, for example, found Salmonella at 86 per cent of flocks.
In the largest study of its kind (analyzing more than 30,000 samples taken from more than 5,000 operations across two dozen countries) cage-free barns had about 40% lower odds of harboring the egg-related strain of Salmonella.
Listeria, yet another bacterial infection, can cause miscarriages, still births, and serious illnesses in newborns. It is particularly a modern problem as Listeria has been found to be able to survive microwave cooking.
Between 1987 and 1989, 26 babies in the UK died from listeriosis. In response, in 1989 the UK Government issued a warning to vulnerable groups, such as preg-nant women, to avoid high- risk foods, such as soft cheeses and meat pates. Listeria continues to be associated with farm animals, and a wide range of food prod-ucts derived from these animals. In particular, Listeria seems to be a significant contaminant of slaughterhouses. One Dutch study found Listeria in 100 per cent of environmental samples taken from the conveyor in a slaughterhouse.
In the US, multistate outbreaks have occurred in each of the last six years, including a four-state, 3-death one associated with dairy products in the southwest in 2015, a two-state, 1 death event again associated with dairy products in 2014, and a well-known 2011 Colorado-sourced outbreak involving cantaloupes which in-fected 147 and killed 33 consumers.
Enterococci are a widespread group of intestinal bacteria that can cause serious infections in other parts of the body. Antibiotic resistance is a major concern with Enterococcus faecium, the strain most commonly associated with illness in people. Accumulating evidence now indicates that the use of the glycopeptide avoparcin as a livestock growth promoter has created in food animals a major reservoir of Enterococci which contain high levels of the gene cluster vanA which encodes for resistance to the antibiotic vancomycin.
A 2011 study shows that house flies and German cockroaches in the confined swine production environment likely serve as vectors and/or reservoirs of antibiotic resistant and potentially virulent enterococci and consequently may play an important role in animal and public health.
Streptococcus is a family of bacteria responsible for many animal and human infections. Many species of Streptococcus can be isolated from normal swine. There is no single, consistent predictor of possible pathogenicity, although environmental or other predisposing factors may influence it. Outbreaks of streptococcal infec-tion in swine occurred many years before the organism, S. suis, was identified in 1987 as a new pathogenic species. Outbreaks of S. suis infection now are re-ported frequently.
Streptococcus suis survives in dust and feces in the usual swine environment. It is present in the feces and nasal secretions of carriers. Transmission may be through ingestion, inhalation or nose-to-nose contact. Flies and rodents may play a role in mechanical spread.
In 2005 the world’s largest and deadliest outbreak of the pathogen Strep. Suis emerged, causing meningitis and deafness in people handling infected pork prod-ucts. Experts blamed the emergence on factory farming practices. Pig factories in Malaysia birthed the Nipah virus, one of the deadliest of human pathogens, a contagious respiratory disease causing relapsing brain infections and killing 40% of people infected. Its emergence was likewise blamed squarely on factory farm-ing.
The bacterium Escherichia coli is a normal inhabitant of the gastrointestinal tract of humans and livestock. It colonizes the newborn’s colon within hours of birth, and serves important intestinal physiological functions for the rest of the host’s life.
The content of one’s food, however, can seriously change what goes on in one’s intestines. Traditionally, cattle subsisted on a grass-based diet. But over the last couple of generations government corn subsidies and consumer demand for more fatty, marbled beef has motivated farmers to switch over to grain-based feed for their cattle. As a result, cows’ digestives systems became more acidic in order to tolerate the grain.
In The Omnivore’s Dilemma Michael Pollan explains what happened next:
“Most of the microbes that reside in the gut of a cow and find their way into our food get killed off by the strong acids in our stomachs, since they evolved to live in the neutral pH environment of the rumen. But the rumen of a corn-fed feedlot steer is nearly as acidic as our own stomachs, and in this new, man-made environment new acid resistant strains of E. coli, of which O157:H7 is one, have evolved.”
This strain has received close attention because, in 1983, it was found that it is no longer killed off in humans’ acidic stomachs and can lead to haemolytic uraemic syndrome (HUS), a form of kidney failure. This is fatal in 10 per cent of cases, and those who recover may have serious long-term impairment of kidney function. Even if HUS does not develop, E. coli 0157:H7 commonly results in severe abdominal cramps, bloody diarrhea, and in some cases vomiting. The infectious dose appears to be very small – ingestion of less than 100 bacteria can produce illness. No specific treatment exists, and the effectiveness of antibiotics remains unclear.
The toxic strains are linked to conditions in beef feedlots, with ground beef is the most common contaminated E. coli 0157 food source for people. A US Na-tional Animal Health Monitoring System study found E. coli 0157 in fecal samples from 63 per cent of cattle feedlots. Slaughterhouses with large numbers of animals and contaminated with gastro-intestinal contents and manure dispersed during slaughter can be expected to offer a route for E. coli to enter the human food chain.
E. coli 0157 has also been found in sheep. Colisepticemia in poultry, caused by E. coli, has also increased with the development of intensive boiler production. In addition, E. coli bacteria cause colibacillosis in chickens, now one of the most significant and widespread infectious diseases in the poultry industry. Studies have shown infection risk to be directly linked to overcrowding on factory chicken farms and among caged egg-laying hens, the most significant risk factor for flock in-fection is hen density per cage.
Methicillin-resistant Staphylococcus aureus (MRSA) is another bacteria that, thanks in part to factory farming, has become a public health problem. Alarming rates of MRSA detection in live farm animals and retail meat in Europe led to increased scrutiny of the use of antibiotics in agriculture, and finally the European Union banned the use of medically important antibiotics as farm animal growth promoters in 2006. But no such comprehensive step has yet taken place in the United States.
Studies of individuals living in proximity to concentrated animal feeding operations support the idea that non-livestock strains may be spreading within areas proximal to farms. Two independent studies carried out in Iowa and Pennsylvania that examined the relationship between animal farms and MRSA found an in-creased risk of MRSA colonization or infection in those living close to such farms or in areas where their manure was spread on fields.
Bovine spongiform encephalopathy (BSE), commonly known as mad cow disease, is a fatal disease in cattle that causes a spongy degeneration of the brain and spinal cord. The disease may be most easily transmitted to human beings by eating food contaminated with the brain, spinal cord or digestive tract of infected carcasses. The infectious agent, however, although most highly concentrated in nervous tissue, can be found in virtually all tissues throughout the body, including blood. In humans, it is known as new variant Creutzfeldt-Jakob disease.
BSE has a long incubation period, about 2.5 to 8 years, usually affecting adult cattle at a peak age onset of four to five years, all breeds being equally suscepti-ble. BSE is caused by a misfolded protein—a prion.
The first case in the United States was announced in 2003 in the state of Washington. In January, 2004 new safeguards against mad cow disease were an-nounced by the Food and Drug Administration, including banning chicken waste from cattle feed and barring restaurant meat scraps from being used in animal feed. Apparently they were acceptable practices until then. Later cases were found in Texas in 2005, Alabama in 2006 and in California in 2012.
Avian and Swine Influenza
Avian flu (H5N1) and Swine flu (H1N1) are highly pathogenic viruses circulating among their respective named hosts, but also able to infect humans.
Pigs are nature’s notorious “mixing bowls” for inter-species infections and many swine flu viruses have long contained human influenza genetic compo-nents. When, in the late 1990’s – industrialized swine production really took off in North America – scientists were alarmed to find that avian influenza ge-netic material was also mixed into the continent’s viral soup.
The Pew Commission on Industrial Farm Animal Production issued a lengthy report on factory farming that included research on emerging forms of avi-an-swine-human influenza viruses. The molecular forensics of rapidly mutating animal pathogens makes epidemiological investigations all the more challeng-ing, it said. “Populations exposed to infectious agents arising in CAFOs are even more difficult to define as some agents – such as a novel avian influenza virus – may be highly transmissible in or well beyond a community setting.”
But the Commission warned:
“The continual cycling of swine influenza viruses and other animal pathogens in large herds or flocks provides increased opportunity for the generation of novel viruses through mutation or recombinant events that could result in more efficient human-to-human transmission of these viruses. In addition, ag-ricultural workers serve as a bridging population between their communities and the animals in large confinement facilities. This bridging increases the risk of novel virus generation in that human viruses may enter the herds or flocks and adapt to the animals.”