CHICAGO (REUTERS) - A swine virus deadly to piglets has been discovered on two hog farms in North Carolina, an official in the No. 2 hog-producing United State (US) state said on Tuesday.

Porcine Epidemic Diarrhea virus (PEDv) was found at a sow farm, where piglets are born, and at a finishing farm where hogs are fattened up for slaughter, said Dr Tom Ray, director of Livestock Health Programs for the North Carolina Department of Agriculture and Consumer Services.

State and federal veterinarian diagnostic lab researchers confirmed the positive tests last week, Mr Ray told Reuters.

Presence of the virus in North Carolina has US investigators concerned about its reach and the difficulty of containing or eliminating it. The vulnerability of baby piglets makes the virus especially troubling for North Carolina, with its heavy concentration of massive sow farms.

Iowa, the largest US producer of swine, has twice as many hogs as North Carolina. But the number of piglets born in North Carolina nearly equaled that of Iowa last year, thanks to these farms that churn out millions of baby pigs annually, said independent livestock market analyst Bob Brown in Edmond, Oklahoma.

While the virus has not tended to kill older pigs, mortality among pigs four weeks old or younger has commonly been at least 50 per cent, and as high at 100 per cent, say veterinarians and scientists studying the US outbreak.

"There's tremendous concern anytime you have a disease that's contagious like this. You have your life, livelihood and family tied up into your operation and anything that is going to threaten that security is of great concern," Mr Ray said.

The virus does not pose any health risk to humans or other animals, and federal officials said meat from PEDv-infected pigs is safe to eat.

Experts do not know how the virus arrived in the US or how many US animals have died in the PEDv outbreak.

Farmers and hog processors have bolstered biosecurity measures in a bid to stop the spread of the virus.

North Carolina is a production hub for Smithfield Foods Inc , whose Murphy-Brown LLC unit has 250 company-owned farms and roughly 1,200 contract producer farms in North Carolina, Pennsylvania, South Carolina and Virginia.

Smithfield's also has pork processing plants in the state, including the world's largest pork-processing plant in Tar Heel, North Carolina.

None of Smithfield's sow farms has tested positive for PEDv, said company spokesman Keira Lombardo. But the company has rolled out "a comprehensive series of procedures" to try to keep the virus out of its operations, "including ensuring that biosecurity procedures are fully compliant and are being effectively monitored, adjusting feed delivery procedures and monitoring industry incidences of PEDv, especially in close proximity to our sow farms."

As of June 22, the virus had spread to 14 states, and at least 265 cases have tested positive, according to data compiled by the US Department of Agriculture.

Independent livestock market analyst Bob Brown in Edmond, Oklahoma, said the number of confirmed PEDv cases is relatively small in a country with more than 68,000 US hog operations.

The genetic structure of the strain of the virus found at US hog farms and slaughterhouses is 99.4 per cent similar to the PEDv that hit China's herds last year, researchers say.

After it was first diagnosed in China in 2010, PEDv overran southern China and killed more than 1 million piglets, according to the Centers for Disease Control and Prevention's Emerging Infectious Diseases Journal.