A new strain of influenza passing from pigs to humans has at least one infectious disease expert calling on state officials to close the swine exhibits at the Minnesota State Fair, which begins on Thursday.

Michael Osterholm, of the University of Minnesota, said that the number of pig-to-human infections has been "unprecedented" this year. And because viruses can change when they cross species, it could set the stage for a major public health threat if people mingle with sick pigs.

"If anything, we're tempting fate," he said Monday.

The state Department of Health confirmed on Monday that the new strain of flu has surfaced in Minnesota, infecting a Twin Cities preschooler and possibly an older sibling.

At this point, the flu is relatively mild and does not appear to pose a public health threat, said Richard Danila, the deputy state epidemiologist. But he said that he plans to talk with federal officials at the U.S. Centers for Disease Control and Prevention (CDC) on Tuesday about "whether or not swine should be banned from the State Fair."

As of Monday, the flu had spread to more than 200 people in eight states, mostly children who had been exposed to pigs at state and county fairs. So far, this flu strain, H3N2v, has shown little ability to spread from person to person, Danila said.

About 1,000 pigs are scheduled to arrive at the Minnesota State Fairgrounds in the next few days to participate in 4-H, Future Farmers of America and open-class competitions in the Swine Barn.

Jerry Hammer, the fair's general manager, said he hadn't heard about Osterholm's call to cancel the swine exhibits at the fair.

"Boy, nobody has gone that far," Hammer said. "Unless we hear something from the Health Department, I don't know if anything else would change on our end."

He said his staff has been meeting regularly with the health department, as well as the Board of Animal Health. "Until the animals get here, it's not too late. But we need a whole lot more information."

Minnesota 4H officials declined to comment, referring questions to the state Health Department.

For now, precautions

Dr. Joni Scheftel, the state public health veterinarian, said Monday it was premature to close the swine exhibits at the State Fair. "We're just trying to get the word out about how people can minimize their risks," she said.

Even before the new cases were reported, state health officials had been urging precautions for fairgoers and swine exhibitors. Among the recommendations: Avoid eating in the swine barn, and wash hands after visiting those exhibits.

On Monday, the CDC recommended that anyone who's sick, or particularly vulnerable to the flu, avoid the swine exhibit. That includes young children, the elderly, pregnant women and people with severe chronic conditions.

Fair officials say their veterinarians will be closely monitoring pigs for signs of illness.

But Osterholm, a former Minnesota state epidemiologist, said the precautions may do little if any good at preventing the spread of the virus.

"As the pigs are being affected, so are the people having contact," he said. "None of us have ever seen this kind of dynamic transmission from humans to animals," he said. He also said there's evidence that healthy-looking pigs can carry the virus.

"If ever we should be avoiding the human-animal interface, this is it," he said.

The two Minnesota children developed flu symptoms two days after visiting a live animal market in Dakota County on Aug. 10, the Health Department said in a news release.

Tests confirmed the virus only in the younger child, but the older child is considered a "probable case," the department said. Both children are said to be recovering.

Michael Schommer, a spokesman for the state Agriculture Department, said that his agency is "following the situation closely," and is advising live-animal markets to take precautions as well "to limit potential exposure."

He said his department would defer to the Health Department on any decision to close the State Fair swine exhibits.

"People should understand this is a virus that can be contracted from live animals but it is not a virus that is spread through the consumption of pork," said Schommer.

Hammer, of the State Fair, noted that during the 2009 H1N1 flu pandemic, a number of 4H members fell ill during the fair.

"Those kids went home early and we did a thorough scrub-down and disinfected where they were at and had no more problems with it," Hammer said.

However, said Osterholm, it's impossible to predict what might happen.

"Each one of these fairs offers an opportunity for this virus to undergo more changes that could lead to a serious public health problem on a global basis."

maura.lerner@startribune.com • 612-673-7384 curt.brown@startribune.com• 612-673-4767