African swine fever, for which no treatment or vaccine exists, has spread to every Chinese province and region, and has also jumped the border into Cambodia, Mongolia and Vietnam. Analysts at the Dutch bank Rabobank, which lends heavily to the global agriculture industry , have predicted that China will produce 150 million to 200 million fewer pigs this year because of deaths from infection or culling. That would be a hefty chunk of the 700 million pigs slaughtered in China in 2018.

The Chinese economy, already slowing, is starting to feel the effects. Higher pork prices helped push inflation to a five-month high in March. The nation’s stock of live pigs has fallen by a fifth from a year ago. The government, anticipating shortfalls, has bought frozen pork to build up its strategic reserve. Hog futures in the United States have rallied as traders bet that China will buy more American meat.

China has introduced new hygiene requirements, imposed quarantines and restricted the transporting of swine. But such measures will be of limited use if the authorities have an incomplete picture of the problem — or if they have more a complete picture that they do not make public.

“There’s no way to control something that you don’t acknowledge exists,” said Christine McCracken, a Rabobank analyst. In places where infections were not reported or acknowledged, farmers and pork producers might not be taking adequate safety precautions , she said. They may even be selling and processing infected animals. African swine fever can linger for weeks or months in uncooked and frozen pork.

“It only takes one infected piece of meat entering the chain to muck it all up again,” Ms. McCracken said.

The government has threatened to punish farms that do not immediately report outbreaks. Across China, though, dead pigs have been found heaped in rivers and ditches, suggesting that farmers disposed of them without notifying the authorities .