African swine fever is decimating the world’s largest hog herd in China, and that holds risk and opportunity for U.S. pork producers.

Affected animals have now been reported in every province in China, and the disease has spread to neighboring Mongolia, Vietnam and Cambodia.

At least 129 outbreaks have been reported since African swine fever was first identified in August, according to China’s National Bureau of Statistics. It estimates that 1 million exposed animals have been exterminated and that the interruption in production has reduced the country’s overall hog population by 40 million.

But experts say infection numbers and the number of culled pigs have been immensely underreported.

“It’s so much more than 1 million pigs, but no one knows for sure,” said Dermot Hayes, an economist at Iowa State University who runs a small center that studies Chinese agriculture. China penalizes the “provinces that report the disease, so reporting is not a good measurement.”

The virus, which is not communicable to humans, can be spread by live or dead pigs, domestic or wild, and via pork products. Symptoms in animals include high fever, weakness, skin lesions, diarrhea, vomiting and difficulty breathing. Death can occur within a week of infection.

There is no treatment or vaccine, and the only way to stop the disease is to cull all affected or exposed swine herds. If that occurs, there will not be enough surplus pork in the world to make up for the anticipated shortfall in Chinese production.

The financial services firm Rabobank has projected a 30 percent decline in Chinese pork production for 2019.

Some analysts say this could lead to a 40 percent increase in the price of pork belly and a surge in demand for other animal proteins, including chicken.

U.S. hog prices have been struggling, so the specter of a Chinese shortfall could be a boon to American producers.

China is the largest producer of pork, with herds six times as large as U.S. populations, and the largest consumer of pork. The Chinese consumed about 56 billion pounds of pork last year, which accounts for more than half the global total.

Even with Chinese tariffs on American pork imports at 62 percent, the U.S. Department of Agriculture estimates the largest demand for U.S. pork in 2019 will come from China. It anticipates that Chinese pork imports will rise 41 percent for the year.

In March, China bought 23,800 metric tons of pork, its biggest purchase in nearly two years.

African swine fever has not been reported in North America, but many in the U.S. pork industry worry what an outbreak could do.

The National Pork Producers Council canceled the 2019 World Pork Expo, held each June in Des Moines, out of “an abundance of caution” amid African swine fever’s spread.

Jaydee Hanson, policy director for the Center for Food Safety, called for additional safeguards to keep pig meat from China out of pig feed.

“The U.S. Department of Agriculture needs to make sure this virus doesn’t come into the U.S. We are a major pork producer — ‘decimation’ would be too small a word,” he said.

Michael Nepveux, an economist with the American Farm Bureau Federation, said it was not an inevitability that the disease will reach U.S. swine populations. China has had foot-and-mouth disease for 15 or 20 years, he said, which so far has not affected the United States. Still, he noted that African swine fever is a hardy virus, one that can remain alive in pelletized animal feed.

“Tainted products could be smuggled in by airline travelers, or it could be in feed ingredients. We do import organic, non-GMO soy animal feed from China and India, and it is potentially a risk,” he said.

Human behavior is also responsible for the spread of the disease, Hayes said, describing how scientists believe the virus got to Belgium.

“A trucker left Ukraine and headed to a port in Belgium. He threw a pork sandwich out the window and a pig ate it. Pigs are omnivores; they scavenge. Mistakes can happen,” he said.

He argued that there is a financial incentive in China for hog farmers to rush infected animals to market rather than cull them, which increases the risk of infected animals being processed at plants that make meat and bone meal that ends up in pet food.

Pet food would be a possible mechanism for the virus to reach the North American hog, Hayes said.

“It would be a strange scenario, someone feeding garbage containing leftover pet food to backyard pigs in the U.S.,” he said.

In March, the USDA announced enhanced biosecurity measures to prevent the disease from spreading to the United States. The agency also expanded its Beagle Brigade, which patrols U.S. ports of entry, to 179 teams across key air and sea ports, where the dogs and their handlers screen new arrivals and check for illegal pork and pork products.

Inspections of garbage-feeding facilities were sped up to ensure material was cooked at a temperature that kills the virus. The USDA also announced research on reliable testing procedures to screen for the virus in grains, feeds, additives and oral fluid samples.

“I don’t believe the Chinese have it under control at this point, and the virus can last for months in refrigerated pork products,” Hayes said. “Our risk increases as more and more of the population around the rest of the globe has some swine fever. ”

Correction: An earlier version of this report erroneously attributed information and quotations to Dave Pyburn, vice president of science and technology for the National Pork Board. This material has now been correctly attributed to Dermot Hayes, an economist at Iowa State University. An earlier headline gave an imprecise impression of the origins of African swine fever. This has been corrected.