A serious threat to hog supplies emerged in August for China, the world’s largest pork consumer and home to more than half of the global population of the animals. That could fuel a bounce-back in hog prices, which have dropped by more than 28% year to date.

China’s Ministry of Agriculture and Rural Affairs reported China’s first case of African swine fever, or ASF, on Aug. 3. The virus is highly contagious, and once infected, pigs usually die within two to 10 days. Humans are not susceptible to the disease.

“ASF...