[D66] Industrial Hog Farms Are Breeding the Next Pandemic

[R.O.]

  Industrial Hog Farms Are Breeding the Next Pandemic

By
Tom Philpott
motherjones.com
14 min
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In March of 2009, people in the rural Mexican village of La Gloria 
started coming down with a nasty respiratory infection. The town, 
located in the state of Veracruz, sat 5 miles from an industrial-scale 
hog farm. Within a few weeks, clusters of this rapidly progressing 
pneumonia arose among Mexico City residents. Researchers soon identified 
the bug as a “novel swine flu.” It quickly jumped to the United States 
and spread worldwide, and in June, the World Health Organization 
declared a pandemic, the first time it had done so since the deadly 
avian flu outbreak of 1968.

The 2009 swine flu strain didn’t turn out to be as deadly as originally 
feared. Although indeed novel, it was similar enough to older flu 
strains that about a third of people over 60—the most vulnerable 
population—had preexisting antibodies to the virus, helping them shake 
it off. Even so, it killed more than 284,000 people around the world, 
including at least 12,469 Americans.

We might not be so lucky next time. As the COVID-19 crisis lingers with 
no end in sight, it’s no fun to think about other emerging contagions 
that could be coming our way. But given the gaping holes the coronavirus 
fiasco has exposed in our infectious-disease response systems, it seems 
prudent to squarely face what’s coming down the pike—in hopes we can 
prepare to do better.

The likely source of the next pandemic is all around us: It’s the same 
one that triggered the 2009 scare. Industrial-scale hog and chicken 
farming—innovated in the United States and rapidly spreading 
globally—provides an ideal environment for the evolution and 
transmission of novel pathogens, especially influenza, that can infect 
people. (Cattle generally aren’t susceptible to human-adapted flus.)

“Another influenza pandemic occurring at some stage of the future is 
exceedingly high,” said Richard Webby, professor of infectious diseases 
at Memphis-based St. Jude Children’s Research Hospital and director of 
the World Health Organization’s Collaborating Center for Studies on the 
Ecology of Influenza in Animals. “The chances that it’ll come from some 
sort of farmed animal—my personal opinion is, that’s high as well.”

Gregory Gray, a professor of medicine, global health, and environmental 
health at Duke University and an expert on animal-to-human disease 
transmission, is even more direct. His biggest worry for the next viral 
pandemic? “Influenza A viruses that originate in pigs,” he said. “Hands 
down.”

The 2009 flu scare inspired the US government to ramp up its effort to 
monitor factory-scale farms for new pathogens, Gray added. But its 
surveillance was limited from the start, and in recent years has dwindled.

Pigs have a special capacity to incubate new viruses. Although birds are 
hosts to many kinds of influenza, avian flus don’t bounce easily to 
humans. There have been some exceptions: The 1997 H5N1 outbreak in Hong 
Kong sickened at least 18 people and killed six. But that event, as well 
as smaller outbreaks since, was relatively easy to control, because once 
the pathogen invaded the human immune system, it didn’t show much 
ability to spread person-to-person. Most infections involved people who 
had been in direct contact with birds.

Hogs are different. While pure swine flus don’t jump easily to humans, 
pigs can catch flu viruses that are from birds and humans, and then pass 
them back and forth. When more than one flu virus has infected a single 
host, the viruses have the sinister ability to swap genes, a process 
researchers call “reassortment.” Like DJs creating something new by 
grabbing and combining snippets from old vinyl records, flus use the 
bodies of pigs to make the viral equivalent of a mixtape. If a pig 
catches an avian flu and a human flu at the same time, the two viruses 
can morph into novel strains that contain swine, human, and avian 
genetic material, with the potential ability to infect all three species.

That’s why many epidemiologists call “mixing vessels” for flu strains; 
they provide a host in which avian- and swine-evolved flus can reach 
people. And since human immune systems have little exposure to bird 
flus, it can be quite dangerous for us when genetic traces of these bird 
flus invade our bodies through a strain that was reassorted inside of a 
hog.

So scientists were alarmed earlier this summer when Chinese researchers 
published a paper in the peer-reviewed US journal /PNAS/ reporting 
that**an “avian-like” swine flu strain had become pervasive in the 
nation’s vast hog operations, containing “all the essential hallmarks” 
of a virus that can cause a human pandemic. The team tested 338 workers 
who routinely come into contact hogs and found that 10.4 percent had 
antibodies to the new strain, meaning they had unknowingly contracted 
and recovered from the virus. They also tested 230 people who aren’t 
associated with the hog industry and found antibodies in 4.4 percent of 
them. In other words, the virus is out there, infecting people and 
evolving; likely being swapped back and forth between workers and hogs.

The strain recently identified in China, known as G4 EA H1N1, is related 
to the H1N1 flu that caused the global pandemic in 2009. The 2009 strain 
contained genes from avian, swine, and human flus—a classic “triple 
reassortment.” It has also taken on avian genes through reassortment 
that makes it novel to our immune systems—meaning it could be very hard 
to fight.

The new flu hasn’t caused major problems yet; it hasn’t proven either 
highly contagious or particularly virulent. But that could change as it 
circulates among the workers and animals in China’s hog industry. The 
fact that it’s out in the world, the paper warns, “greatly enhances the 
opportunity for virus adaptation in humans and raises concerns for the 
possible generation of pandemic viruses.” The WHO’s Webby put it like 
this: “It’s a numbers game. These viruses throw out mutations every time 
they replicate, so the more chances the virus gets, the more 
interactions with humans, the more chance that one day the stars will 
align in the right order, the virus will get the right mutation, and 
take off.”

Changes in our eating habits and farming practices have dramatically 
ramped up pigs’ propensity to gin up new pathogens. Humans domesticated 
them at least 9,000 years ago, and we’ve probably been swapping flus 
with them ever since. But for almost that entire history, hog farming 
was essentially a backyard activity, with relatively few animals per 
operation, and broad genetic diversity in the population. The numbers 
game Webby describes exists when hogs are kept on a small scale, 
outdoors, with the herds largely isolated from each other. But what’s 
happening now is different.

Starting in the 1980s, US pork packers began to change their model, 
inspired by what the poultry industry had done decades before. Instead 
of buying hogs from small producers, meatpacking companies moved to a 
vertically integrated model, pushing to source their pigs from large, 
confined operations working under production contracts.

The shift turned the industry upside down. According to US Census of 
Agriculture figures, in 1982, 330,000 farms raised 55.4 million hogs. By 
2017, just 66,000 farms were churning out more than 72 million pigs. In 
other words, 80 percent of US hog farms exited the business over that 
period even as total output jumped 21 percent—and so the average number 
of hogs per farm spiked from 168 to 2,000, a 12-fold increase. And that 
figure understates the scale of modern hog production. The 2017 Ag 
Census show that three-quarters of US hogs are raised on the 3,600 
largest operations, each averaging more than 14,000 animals.

Today, an industrial-scale hog “barn” is an enclosed facility holding as 
many as 4,440 pigs. A typical operation consists of several of these 
buildings clumped together, each with ventilation systems that has the 
potential to suck up airborne flu pathogens from each barn and pass them 
to the barn next door.

China’s pork sector, the globe’s largest, is rapidly mimicking the US 
model, though it’s at an earlier stage of the trajectory. Between 1975 
and 2013, growth in China’s pork consumption rose by a factor of eight. 
(Though this growth has flattened in recent years.) Giant factory 
facilities took the place of the micro-scale operations that had 
sustained the region for centuries. In 2000, 74 percent of Chinese pork 
production came from backyard farms. By 2015, household sources were 
providing just 27 percent of the nation’s domestic pork. The 
contribution from commercial farms with at least 1,000 hogs, meanwhile, 
tripled over that decade.

What could possibly go wrong? Rob Wallace, an evolutionary biologist 
with the Agroecology and Rural Economics Research Corps and author of 
/Big Farms Make Big Flu/, argues that the industrial animal farming 
model delivers a perfect habitat for flus to proliferate, evolve, 
mutate, and adapt—to essentially hack the numbers game for creating 
pandemic strains. Factory-scale farms provide a huge playground for 
human and avian flus to “trade multiple combinations of genetic 
segments,” he said. They’re “an explosive evolutionary accelerant.”

For most of the 20th century, the flus circulating among US pigs didn’t 
evolve much genetically, meaning our immune systems had plenty of time 
to adapt the ability to fight them off. It wasn’t until the 1990s—when 
the consolidation of US hog production was reaching a crescendo—that pig 
flus began to reassort wildly with human and avian flus and create new 
strains that can jump to people. In a prescient paper he co-authored 
with other researchers, published five years before the 2009 outbreak, 
the WHO’s Webby sounded the alarm. “The influenza reservoir in the 
United States swine population has thus gone from a stable single viral 
lineage” to a “dynamic viral reservoir containing multiple viral 
lineages,” making the US swine population an “increasingly important 
reservoir of viruses with human pandemic potential,” they wrote.

In addition to capitalizing on the sheer number of potential hosts 
breathing in each other’s exhalations and excretions in a modern hog 
facility, viruses also take advantage of the pigs’ genetic similarity. 
With a genetically diverse drove, some pigs will have a mutation in 
their immune systems that blocks infection, limiting the pathogen’s 
range. But “if you’ve got a couple thousand genetically similar hogs 
packed in a barn, then it’s all food for flu,” Wallace said. As the 
industry breeds hogs to deliver consistent, uniform pork products, the 
genetic diversity of hog populations erodes, and what Wallace calls an 
“important firewall” to developing pandemic flu strains crumbles.

The workers who tend these pigs are prime targets for moving the virus 
into surrounding communities. And global trade ensures that the flu can 
travel the world. “The United States and Canada, the largest exporters 
of hog, are also the largest exporters of swine flu,” Wallace said. 
After the North American Free Trade Agreement of 1994, Mexico began to 
dramatically scale up its own hog sector, leaning heavily on hogs 
imported from the United States and Europe. That flow of hogs and their 
attendant flus is the likely source of the 2009 triple-assorted pandemic 
strain, a 2016 analysis by US, Mexican, and European researchers shows. 
Wallace also points to a 2015 /Nature/ study by a global team led by US 
National Institutes of Health researchers with a chart showing how flu 
bugs circulating on US farms disperse globally:

The US pork industry, for its part, asserts that the workers who tend 
hogs are unlikely to swap viruses with them, because hog farmers follow 
stringent biosecurity measures. “Modern US pig barns are designed 
specifically for pig health and safety,” Jason Menke, director of 
marketing communications for the National Pork Board, wrote in an email. 
Farmers wear special boots and clothing that stay in the barn. Many 
farms require caretakers to shower in special facilities attached to the 
barn, which “minimizes the chance that the pigs will be exposed to a 
pathogen that will make them ill.” Workers are also “encouraged” to wear 
personal-protective gear like masks to “protect themselves from both 
illness and injury working on the farm,” Menke wrote. He added that 
“sick leave policies encourage workers to stay home when ill to prevent 
unnecessarily exposure to other workers on site or to the pigs, since 
pigs can be infected with human influenza strains.”

But no biosecurity system is perfect, Wallace counters. In a 2015 paper 
looking at flu strains circulating on US pig farms, the National 
Institutes of Health and US Department of Agriculture researchers found 
that, despite the industry’s biosecurity efforts after the 2009 H1N1 
pandemic, industry workers “continuously” kept reinfecting the US hog 
herd with their flus. That meant hogs, mixing vessels for human and bird 
flus, got a steady infusions of human-adapted flus, free to re-assort 
and create novel strains that can infect people.

Wallace thinks that factory-scale livestock farming inherently generates 
viral pandemic threat, and should thus be dismantled—a view that gained 
political traction late last year when Sen. Cory Booker (D-N.J.) floated 
a bill that would do just that. Booker’s proposal, which has since 
gained support from Sen. Elizabeth Warren (D-Mass.) and Rep. Ro Khanna 
(D-Calif.), remains unlikely to pass; the meat industry remains a 
powerful lobbying force in Washington. But as Ezra Klein recently 
reported in /Vox/, an “odd-bedfellows coalition” of animal-rights 
activists, economic populists, and small-scale farmers is rallying 
around it.

Mainstream university-based flu researchers are far more cautious about 
challenging the industry so directly. While Duke’s Gray insisted that 
the next pandemic might come from hogs, he does not advocate for banning 
industrial hog farming. “We have some of the safest and lowest-cost pork 
production in the world, and that’s wonderful,” he said. “And we are 
exporting that technology to many places around the**world and they’re 
all shifting to large-scale farming—it’s the way to go to keep the hogs 
safe and produce low cost meat.”

He adds, however, that the pork industry and the US Department of 
Agriculture—which regulates the safety of meat production—aren’t doing 
enough to monitor the viral pathogens that can flourish on large hog 
operations. Through surveillance, researchers can see what’s out there 
and kick-start the development of human vaccines when novel strains emerge.

Back in 2010, in response to the previous year’s pandemic, the Animal 
and Plant Health Inspection Service (APHIS), a division of the US 
Department of Agriculture, launched a program to monitor and analyze 
flus circulating in the hog population. It’s an important but limited 
effort, Gray said. It relies on hog producers and veterinarians to swab 
animals showing flu symptoms (coughing, sneezing, runny nose, etc.) and 
send them in to USDA-affiliated labs. Gray characterized the program as 
“very spotty” because of its focus on “passive” testing, which relies on 
farmers to volunteer samples from sick animals.

Active testing, on the other hand, would randomly select samples from 
both visibly sick and asymptomatic animals. “There are influenza viruses 
that infect both humans and pigs [but] do not necessarily cause signs of 
infection in both,” he said. Similar to how people can be infected with 
COVID-19 and spread it without showing symptoms, pig flu often hides in 
animals that appear healthy. “Hence, I have long argued that passive 
surveillance among only sick pigs has the potential to miss novel 
emerging swine influenza viruses that may harm humans.”

The US hog industry is “really good” at detecting and preventing the 
spread of diseases that make pigs sick and lower production, Gray says. 
But viruses that don’t directly harm hogs—including those that might do 
worse damage to humans—”are tolerated, permitted to spread and to mutate.”

Worse still, Gray adds, as the 2009 flu pandemic recedes into the past, 
funding for the APHIS surveillance program—and the participation of hog 
farmers—has dwindled. In the agency’s most recent report on the program, 
released in July 2020, total samples received from farmers peaked in 
2015 at 35,792 and had fallen to 3,098 in 2019. An APHIS spokesperson 
attributed the drop to changes made in 2016 to shift costs from the USDA 
budget on to hog farmers.

Meanwhile, influenzas aren’t the only viruses that circulate on hog 
farms. Coronaviruses do, too—like the porcine epidemic diarrhea virus, 
which killed 10 percent of US hogs in 2013-14. (PEDV does not infect 
humans). As for SARS-CoV-2, the coronavirus causing the current COVID-19 
pandemic, a study released in June by Chinese researchers found that 
pigs are at least theoretically susceptible: They have lung and kidney 
cells that can be invaded by this particular pathogen. But laboratory 
attempts to infect pigs with it have so far not succeeded. “Given that 
the COVID-19 pandemic is still progressing and SARS-CoV-2 strains are 
constantly evolving,” they wrote, “we need to keep monitoring and 
evaluating the possibility of pigs to become intermediate hosts” of the 
pathogen.

Gray finds the prospect of hog-adapted SARS-CoV-2 daunting. As they do 
for flu, pigs could emerge as what disease researchers call a 
“reservoir” for the pathogen—a large host population that keeps the 
pathogen circulating, giving it more opportunity to infect people. “My 
chief concern is that the current SARS-CoV-2 virus adapts to commercial 
hogs, becomes amplified in them, and cause*s* widespread infections, 
increasing the risk of the virus moving from the pigs to infect humans 
who have not been previously infected,” he said. He expressed an even 
darker possibility: The “remote chance” that if it does manage to enter 
the pig population, it could mutate into something different, yet 
another “novel coronavirus” that would require a whole new scramble for 
a vaccine.

“Honestly, I don’t know if we’re much better off post-2009 than we were 
pre-2009,” the WHO’s Webby said. Governments devoted resources to 
preventing the next big flu outbreak for a few years, but interest faded 
as the event receded into the past, he said. With COVID-19, “we’re 
really seeing for the first time in most people’s living memory the 
impacts these pandemics can have on society. So I’m hoping a silver 
lining from this will be more sustained resources into preparedness.”*
*

Another possibility would be to rethink how we produce meat. The 
coronavirus pandemic has sparked calls to ban “wet markets”—the informal 
food markets that often include live wild animals, the possible point at 
which SARS-CoV-2 jumped from bats to people. As Wallace points out, 
globally, the biomass of the animals we eat—their sheer physical 
weight—is now “far greater” than their wild counterparts. “Planet Earth 
is basically Planet Farm,” he said. “When you populate the globe with 
cities of hogs and poultry, you’re going to generate novel pathogens” 
that confound human immunology, he added. Maybe the fear of another 
pandemic will finally force us to ramp down the scale of our livestock 
operations and adapt to diets that depend on way less meat.

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