African Swine Fever Would Spread Rapidly Through U.S. Pork Industry, Study Finds

An outbreak is killing pigs around the world, and would likely spread quickly in the United States.

image of pig on industrial farm staring at camera, african swine fever study

Reported Food Industry

Researchers are warning that, even with control measures quickly put in place, the U.S. pig industry would be impacted significantly by an outbreak of African swine fever, a disease likely to present a mortality rate of up to 100 percent among infected pigs. An outbreak could cost as much as $80 billion as it spreads through the southeastern U.S., the new study in Preventive Veterinary Medicine finds. Worse, because infected animals may be asymptomatic, the disease could quickly spread from farm to farm before it is detected.

The Impacts of African Swine Fever

The illness which the USDA calls a “highly contagious and deadly viral disease affecting both domestic and feral swine of all ages,” can be transmitted in multiple ways. Animals may become infected through the spread of bodily fluids or when they are fed contaminated pork from other pigs, according to the FDA. Ticks can also become vectors for African swine fever.

PigSpread, the research model used in the new study, revealed that farm-to-farm spread would account for 71 percent of transmission, with local and transportation-related spread each contributing 14 percent. “[O]ne very important variable here is vehicular transmission,” says researcher Gustavo Machado, an author of the study. “This dissemination route has never been studied at a large scale, but here it has shown to be pivotal in disease spread.”

The researchers, who found that an outbreak is likely to last more than 140 days — and could lead to the deaths of nearly half a million pigs —caution that even these startling findings are optimistic. The reality could be even worse, agrees veterinarian and animal welfare scientist Walter Sanchez-Suarez.

“We know from other regions, this would be a very challenging situation. It would be very difficult to control,” says Dr. Sanchez-Suarez, who researches animal welfare, public health and sustainable food systems at Mercy For Animals. To him, African swine fever’s hold on China is a prime example.

The disease was first documented in Kenya in 1921, and later spread through Europe in the 1950s. The FDA reports that swine fever has resulted in “significant pig losses” in places including China, nations of Africa and the EU, Mongolia and Vietnam. It was first detected in Asia in 2018, and a 2018-2019 outbreak led to the death or culling of nearly 25 percent of China’s pig population

“In China, it’s been there since 2018 as far as we know, and the situation has been very challenging,” says Sanchez-Suarez. “They haven’t been able to control the disease and eradicate it.”

“It would be really surprising if this outbreak could be controlled as fast as 140 days, as the study described,” he cautions. “In China and the EU, this has been going on for years.” 

As for the likelihood that swine fever will soon infect pigs in the highly industrialized U.S. pork industry, the veterinarian believes it is highly likely.

“We are talking about a swine population in North America that haven’t been exposed to this virus, and that are genetically uniform, so we have a very fertile scenario for the virus to spread,” says Sanchez-Suarez. “The disease is a very problematic disease with a high mortality, and symptoms that imply lots of suffering for these animals.”

Suffering for Pigs

Sanchez-Suarez concurs with the scientists behind the new study that some pigs may be asymptomatic — and also believes that the initial symptoms of swine fever may not be so easy to identify. The disease often starts out with “nonspecific symptoms” common to many illnesses, such as a lack of appetite, listlessness and fever. “Those signs are very general,” he says. “It could take some time for farmers to figure out what’s going on.”

Symptoms of African swine fever, for those animals who do exhibit outward signs of illness, may include hemorrhaging, skin lesions and more. 

Although swine fever would almost certainly prove fatal to infected pigs, the scientists do emphasize that measures to control the disease’s spread between animals and farms — including surveillance, quarantine and the “depopulation” of pigs — could reduce spread by 79 percent. Nevertheless, a significant amount of damage would  be done even withthese efforts.

“The model shows that policies we have in place would have a positive effect on an outbreak overall, but we need to further investigate this scenario to determine what exactly is required to get it under control,” says Machado.

This means that many pigs on crowded factory farms would almost certainly be culled in large numbers, as has been the case with outbreaks of avian flu. Pigs are often culled en masse through the use of what’s known as “ventilation shutdown plus,” in which all of a barn’s fans and vents are shut down, allowing the temperature to rise as heat or carbon dioxide gas are added.

Dr. Sanchez-Suarez believes that this highly controversial culling method would most likely be used, as there are few ways to cull a large number of farmed animals at once. “This is a very brutal way to end the lives of these animals,” he says, “terrible in terms of animal welfare.”

Ventilation shutdown plus is approved by the American Veterinary Medical Association (AVMA), but animal advocates and veterinarians have called it inhumane, allowing pigs to slowly die as they overheat and suffocate. Use of this method increased as the COVID-19 pandemic slowed operations on farms, and in 2020, undercover footage revealed pigs squealing as they took hours to die in an unventilated barn. Still, some pigs survived even this — and were then killed via captive bolt stunning. While the AVMA generally believes this ventilation shutdown plus is humane, it does stipulate that “failure to achieve 100% mortality in depopulation is unacceptable.”  

A Danger to the Food System & Vulnerable Communities

In many countries around the world, African swine fever could significantly impact humans, even though they cannot become ill with the disease themselves. 

The World Organization for Animal Health writes that while African swine fever does not pose a threat to human public health, “it has devastating effects on pig populations and the farming economy.” Pork is “one of the primary sources of animal proteins” globally, the group reports, comprising over 35 percent of the world’s meat consumption. 

“The spread of ASF across the world has devastated family-run pig farms, often the mainstay of people’s livelihoods and a driver of upward mobility. It has also reduced opportunities to access healthcare and education,” the organization writes.

Outbreaks within the U.S. would likely affect other nations as well, as the U.S. produces 11 percent of the world’s pork. The U.S. exported nearly 2.8 million tons of pork in 2022.

“It is not only about pigs, but about how the food system would be disrupted. We saw with eggs, how the prices skyrocketed [due to avian flu outbreaks],” says Sanchez-Suarez. “There could be scarcity of pork, prices would go up. We are entering the realm of food security, and these types of industries are very vulnerable.” 

‘Problems for Which We Don’t Have Solutions’

Currently, there is no vaccine to protect pigs from this disease, although the FDA states that efforts to develop an African swine fever vaccine and other “mitigation strategies” are ongoing. 

According to Mercy For Animals, more must be done to address disease in the U.S. pork industry in general. The organization recently urged the Biden administration to “protect pigs” from disease, and do more to ensure that pigs “downed” by illness do not end up in the nation’s food supply.

To Sanchez-Suarez, these issues all point back to the same problems inherent in the factory farming of animals, which emphasizes profit over both animal welfare and public health, while facilitating the spread of diseases that can quickly spiral out of our control.

“We are playing with fire,” he says. “We are creating problems for which we don’t have solutions.”

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