Another global pandemic is spreading—among pigs

2021-10-12

A DISEASE OUTBREAK blossoms in China. Exactly how it emerges, far from the eyes of any surveilling scientist, no one can quite explain. It spreads with incredible speed, killing in wide swaths, freezing transport and trade, and causing vast economic disruption. Hitchhiking on global travel, it circles the world. There is no cure, and no vaccine. Inevitably, it arrives in the Americas, in July 2021.

Yup, 2021. The year is not a typo. This outbreak isn’t Covid; it is a parallel, hidden pandemic, a deadly animal disease called African swine fever that was detected in the Dominican Republic in July. African swine fever poses no risk to humans, but it is incredibly destructive to livestock: Those deaths in China were millions of pigs, at least one-quarter—and possibly one-half—of the entire herd of the world’s largest pork producer.

In the United States, animal health authorities are now on high alert. The US Department of Agriculture has pledged an emergency appropriation of $500 million to ramp up surveillance and keep the disease from crossing borders. African swine fever is so feared internationally that, if it were found in the US, pork exports—worth more than $7 billion a year—would immediately shut down.

“Long-distance transboundary spread of highly contagious and pathogenic diseases is a worse-case scenario,” Michael Ward, an epidemiologist and chair of veterinary public health at the University of Sydney, told WIRED by email. “In agriculture, it’s the analogue of Covid-19.”

As with the Covid pandemic at its start, there is no vaccine—but also as with Covid, there is the glimmer of hope for one, thanks to basic science that has been laying down findings for years without receiving much attention. Two weeks ago, a multinational team led by scientists at the USDA’s Agricultural Research Service announced that they had achieved a vaccine candidate, based on a weakened version of the virus with a key gene deleted, and demonstrated its effectiveness in a field trial, in pigs, in Vietnam.

The vaccine candidate is being developed by a commercial partner, a Vietnamese company called Navetco, on a timeline that isn’t yet clear. It’s the fifth experimental vaccine developed by the USDA team. (The first four are being developed by private companies without further federal involvement.) “As far as we know, we have the most advanced African swine fever vaccine in the process of commercialization,” says Douglas Gladue, a microbiologist who is one of the developers.

To step back a bit: African swine fever is a longtime agricultural foe. Though it devastated China’s pork industry, China isn’t the disease’s place of origin. The story of African swine fever actually does begin in Africa, almost exactly 100 years ago.

A Scottish veterinarian named Robert Eustace Montgomery, who was working for the British colonial government in East Africa, published the first description of it, in September 1921. Montgomery reported outbreaks of a hemorrhagic illness in farm pigs that was so destructive “an owner … must be prepared for a practically total loss,” he wrote.

The new disease, caused by a virus, became a regular companion to farming in East Africa. Wild swine and warthogs harbor it and periodically spread it to livestock; so do certain species of ticks that feed on swine. The symptoms were always the same: Pigs would develop fevers, lose their appetites, develop bleeding under their skin and in their internal organs, and collapse. Whenever an outbreak flared, it either burned through a herd and killed all the pigs or was quenched when farmers slaughtered their pigs to stop it. The first farmers to observe the disease found that nothing could prevent it other than keeping pigs confined instead of letting them roam free, and building fences strong enough to keep wild swine out.

Once the virus was discovered, agriculture experts assumed the main route of transmission was direct contact, a healthy pig being exposed to a sick one’s body fluids and feces. But the disease’s first appearance in Europe showed that proximity wasn’t the only risk. In 1957, crews cleaning an airplane that had traveled from Africa to Lisbon threw out leftover in-flight meals. The food went into the airport’s garbage dump, and a herd of feral pigs invaded it. Among the food was ham sandwiches. The outbreak that erupted after the pigs ate the sandwiches showed for the first time that the virus also could travel in pork, even if it had been cooked or cured.

If that sounds like a formidable pathogen—yes, that’s right. Portugal snuffed out that 1957 outbreak, but the disease kept being transported from East Africa into Europe. Research showed that the virus could remain stable in the environment, outside a pig’s body, and could cling to clothing and farm equipment and contaminate dried feed, which is traded around the world.

That might help explain how it leapfrogged such long distances: It arrived in the Republic of Georgia in 2007 and then moved through the Caucasus and into Asia. It landed in China, the home of 45 percent of all the world’s pigs, in 2018. In one year, according to a paper published in September in Nature Food, it killed or caused the slaughter of more than 43 million pigs, costing China more than $111 billion.

Those numbers—which are much larger than the Chinese central government ever admitted to—were tallied before the Covid-19 pandemic began to chill world trade. But the researchers say the disease continues to simmer in China. They predict that if the country cannot get it under control, a further outbreak could cost more than 1 percent of its annual gross domestic product, almost $200 billion.

And now the disease is in the Americas, on the doorstep of the US. African swine fever has been in this hemisphere once before, with terrible consequences. In 1983, it appeared in Haiti, possibly due to an accidental importation from Brazil. To shut that outbreak down, the US and the Organization of American States forced the slaughter of all the swine in Haiti, taking away a crucial underpinning of its fragile rural economy and extirpating its treasured, locally adapted Creole pig. That 1983 slaughter demonstrated that African swine fever isn’t just a profound animal disease; it also is an agent of severe economic damage. It cripples farms and also undermines rural economies.

This time, the disease has been found in multiple locations in the Dominican Republic and was identified in Haiti in September. If it comes to the US, its arrival and the measures needed to control it would threaten feed sales, equipment leases, truck transport, slaughterhouses, and the social fabric of small towns.

“The US is the largest pork exporter in the world,” says Andres Perez, a veterinary epidemiologist and director of the Center for Animal Health and Food Safety at the University of Minnesota. “If African swine fever were to enter the US, there would be an extreme impact on the economy of a number of states. That is why it should be a concern for the public.”

If the disease were detected in the US, the USDA would oversee comprehensive animal slaughter—delicately called “depopulation”—at the farm where it was found, ones nearby, and also farms that had any contact with the first farm via movement of people, trucks, rented-equipment operators, or field reps. At the same time, the agency would order a “national movement standstill” of all swine in the US (and even swine semen being shipped somewhere) for at least 72 hours. Depending on the location, the agency might also send out teams to hunt feral hogs that might be involved.

Because those measures would be so dire, the USDA already is imposing the preventions it is legally allowed. The US had previously forbidden importation of pork from Haiti and the Dominican Republic because of concerns over other animal diseases. Now it is also blocking importation of any pigs, tissue, or semen, and pork or pork byproducts, from the US territories of Puerto Rico and the US Virgin Islands, which are close to Haiti. (The disease has not been detected in either territory.) That’s in addition to putting strict new controls on rescue animals—dogs, for instance—being brought into the country from places where African swine fever is extant, a loophole that had infuriated North Carolina hog producers two years ago when Chinese strays were adopted into their state.

The challenge, says Raymond Robert Rowland, head of the department of pathobiology at the University of Illinois College of Veterinary Medicine, is that African swine fever—known to veterinarians as ASF—is a disease spread by movement. And as Covid demonstrated, the world is more linked by international movement than it has ever been. So a person who walks through a farm, stockyard, or abattoir where African swine fever is present could pick up the virus on their shoes or clothing and carry it with them as they fly across the world.

That might be the pathway African swine fever followed to reach the Caribbean this time—but, Rowland points out, the transfer may have occurred in other ways. “Where do people come from to vacation in the Caribbean?” he asks. “Name a country in the world: Eastern Europe, China, Africa, all areas that have ASF. You can easily think of a scenario where someone brings in a contaminated product, discards it into compost or garbage, and feral pigs come along and pick it up.”

There are more sinister avenues by which the disease could be imported, through criminality instead of carelessness. In 2019, port authorities seized more than 1 million pounds of pork products that were being smuggled into the US, in 50 shipping containers packed with laundry detergent, in order to bypass agricultural controls. The products came from China, and they were shipped out just as African swine fever was hitting its peak there. That may have been the largest pork interdiction at US borders, but it’s far from the only one: Pork is the single most-seized food item at airports and land crossing, according to an analysis of customs data that Bon Appetit conducted in 2014.

Pork that gets nabbed at the border (random examples: ham sandwiches in 2016, sausages in 2018, bologna in 2019 and this year) is incinerated. But pork that isn’t detected, and gets discarded in the US—to evade detection, or maybe just because it’s gone bad—could spark a chain of infection here. Analysts are convinced the vast expansion of African swine fever in China was triggered by feeding pigs swill, an industry term for a mix of discarded human food, cooked and raw food-waste garbage, used cooking oil, and abattoir leftovers such as guts and bones. That same practice, known in this country as “garbage feeding,” is legal in 27 states.

All of which makes it clear how vital achieving a vaccine against the disease will be. Dozens of approaches have been tried over the years, but the research announced by the USDA in September appears the closest to making that hope into reality. (The four other candidates from the same research team are being developed by companies that have not disclosed what progress they have made.) This version was developed by deleting a gene in the virus that had not previously been characterized but turned out to code for how virulent the disease is. With that gene deleted, the virus was attenuated—or weakened—and was administered as a vaccine. It created immunity in all members of the small group of pigs that received it.

Many steps lie ahead, but as the Covid pandemic demonstrated, public health emergencies can force pharmaceutical innovation. It would be good for the pigs of the world—and for biosecurity and the food supply—if this animal health emergency could do the same.

wired.com, 12 October 2021
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