BISMARCK, N.D. — Three pigs exhibited at the North Dakota State Fair in Minot last month have tested positive for a strain of swine flu but it does not appear that the illness has spread to people.

Results from the National Veterinary Services Laboratory show the pigs tested positive for the H3N2 influenza virus, according to the state Agriculture Department. Officials said influenza can spread from pigs to people, but there is no evidence that any people have become ill due to exposure to the State Fair pigs.

However, state officials said anyone who experiences symptoms such as fever, cough, sore throat, headache and body aches after contact with animals should contact a doctor.

State animal health officials inspect all livestock displayed at the State Fair, which was held July 18-26. The pigs appeared healthy when they arrived at the fair and became sick later. Their owners removed them after they were tested, at the recommendation of veterinarians. State officials did not disclose who owned the pigs, where they came from or what happened to them.

It's the first time a flu virus has been confirmed in pigs at a North Dakota fair, according to the state Agriculture Department.

"Fairs and exhibits are an excellent way to showcase livestock and expose the public to animal agriculture production," state Agriculture Commissioner Doug Goehring said in a statement. "When appropriate precautions are taken, there is minimal risk of spreading disease to the public."

The H3N2 virus was first identified in U.S. pigs in 2010. A surveillance program run by the U.S. Department of Agriculture's Animal and Plant Health Inspection Service found 73 positive tests in fiscal 2011 and 138 in fiscal 2012. It was identified in people in 2011, with 12 human cases in the U.S. that year, 309 cases in 2012 and 19 in 2013, according to the U.S. Centers for Disease Control and Prevention.

Most infections were associated with prolonged exposure to pigs at agricultural fairs, and there has been no sustained spread of the virus, according to the CDC.

"It's possible that sporadic infections and even localized outbreaks among people with this virus will continue to occur," the CDC said in a statement.

Vaccines are available to help prevent influenza in pigs, State Veterinarian Susan Keller said.

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