U.S. authorities have started active preparations in response to the rising threat of an outbreak of African swine fever, the deadly disease that has decimated the Chinese pig population and is spreading across Asia.

The Agriculture Department’s Animal and Plant Health Inspection Service led several functional exercises and drills late last month, working off a scenario of an outbreak of the virus in Mississippi that traveled across state lines before it was discovered. Fourteen states participated in the drill.

“We got everyone involved in terms of state troopers, diagnostic labs, private veterinarians and state officials, trying to figure out where the virus was,” said Dave Pyburn, the senior vice president of science and technology for the National Pork Board. “As far as controlling it here, the closer we can get to that index case [the first identified case in an outbreak], the better we can control it.”

Experts say the most likely vector for the disease arriving in North America is tainted animal feed.

According to the World Organization of Animal Health, the disease has spread to more than 50 countries. As many as half of China’s pigs, an estimated 300 million, have died of the virus or been exterminated since the disease took hold 13 months ago. In the past months it has advanced to Vietnam, Laos and South Korea. At the beginning of September, the Philippines confirmed African swine fever in at least seven villages near Manila, requiring 7,000 pigs to be euthanized. And at the end of September, East Timor reported more than 100 cases to the World Organization for Animal Health.

With these developments, the American pork industry has begun mobilizing. Experts say the risk of a domestic outbreak of African swine fever is increasing.

“It’s a higher probability, that’s for sure,” Pyburn said. What are the odds? I don’t have a precise number I can give. But take a look at what this virus is doing around the globe today. And then look at the way goods and people travel. This would have a devastating effect on our industry. It’s the nastiest disease we have on the planet.”

A domestic outbreak could have consequences well beyond the pork industry (which Pyburn said could run into billions of dollars). Widespread loss of pigs could devastate the corn and soy industries, which are primary feed sources, and industries such as beef could be affected by a loss in consumer confidence.

Infected pigs go off their feed, Pyburn said. They don’t want to move and suffer a high fever. By Day 5 there is a hemorrhagic disease in the pigs, bleeding throughout the body and in the organs. By the end of the second week, 85 to 95 percent of the pigs die. There is no vaccine or treatment. The virus can live for weeks on infected slaughtered meat or cold cuts, on tainted feed, and on animal feed additives.

While causing high mortality in domesticated and wild pigs, the disease does not infect humans. The only member of the Asfarviridae family, the virus needs to get inside of cells to replicate. According to Pyburn, it requires receptors on host cells and pigs are the only ones with the proper receptors.

But because there is no vaccine or cure, preventing an outbreak is of paramount importance.

There is insufficient American organic soy, so hog farmers wishing to feed their animals organic soy often import it from China. And there are feed ingredients — B vitamins and trace minerals — that are manufactured only in China. The virus can survive for up to a month on these products, so they must be quarantined and heated to kill the virus.

“If it was me, I would ban the importation of soy products from African-swine-fever-infected states,” said Scott Dee, director of research for Pipestone Veterinary Services, who has been studying viral movement in animal feed under a Foundation for Food and Agriculture Research grant. Canada requires a permit for soy products and has a 30-day quarantine period. Dee said a lot of U.S. companies are adopting a similar approach.

But this isn’t the only risk for an outbreak. Dee said the virus could also be carried by human travelers via the illegal smuggling of meat or other infected food. In many parts of the world, wet markets spread the virus, the kinds of markets where live animals might be at one end of the street, with butchered products for sale at the other. And the practice of feeding pigs “swill” or leftover people food introduces opportunities for tainted meat to be fed to live animals.

The USDA has outlawed raw swill, as a way of preventing an outbreak of African swine fever, requiring that swill be boiled for 30 minutes and cooled before being fed to pigs, said Timothy Kurt, the scientific program director for Foundation for Food and Agriculture Research.

But it is difficult for the government to monitor compliance, and because these practices are time-consuming and expensive, experts say some operators could take shortcuts.