John Goihl, a hog nutritionist in Shakopee, Minnesota, knows a farmer in his state who lost 7,500 piglets just after they were born. In Sampson County, North Carolina, 12,000 of Henry Moore's piglets died in three weeks. Some 30,000 piglets perished at John Prestage's Oklahoma operation in the fall of 2013.

The killer stalking U.S. hog farms is known as PEDv, a malady that in less than a year has wiped out more than 10 percent of the nation's pig population and helped send retail pork prices to record highs. The highly contagious Porcine Epidemic Diarrhea virus is puzzling scientists searching for its origins and its cure and leaving farmers devastated in ways that go beyond financial losses.

"It's a real morale killer in a barn. People have to shovel pigs out instead of nursing them along," Goihl said.

Since June 2013 as many as 7 million pigs have died in the United States due to the virus, said Steve Meyer, president of Iowa-based Paragon Economics and consultant to the National Pork Board said. United States Department of Agriculture data showed the nation's hog herd at about 63 million as of March 1, 2014.

PEDv was first diagnosed in Ohio last May and has spread within a year to 30 states with no reliable cure in sight. U.S. packing plants may produce almost 2 percent less pork in 2014, according to Ken Mathews, USDA agricultural economist.