The virus, called H3N2v, creates flu symptoms in people who have come in contact with infected pigs. It is much less contagious than its sister virus H1N1, commonly referred to as swine flu, because it does not pass from person to person. It can only be contracted by touching swine.
Of the 16 most recent H3N2v cases, none of which required hospitalization, almost all were children exhibiting pigs at county fairs, said Dr. Russ Daly, SDSU Extension veterinarian and state health veterinarian.
While there have been no reported cases of the virus in South Dakota, it is probably here and would cause signs in pigs just like any swine influenza virus, he said.
In addition to flu from pigs, other animal diseases can be passed on to humans, including some species of ringworm.
The chances of contracting an illness from animals at the fair is very small, said Dr. Jim Bain, a veterinarian from Frederick who has been examining fair animals for 39 years.
Bain, who was named 2011 state veterinarian of the year, screens animals for illness before they can enter the fair barns.
He and other veterinarians conduct animal health exams within 10 days before the start of the fair. Any animal with an illness is not allowed to register. Health papers are completed for all animals.
On Friday, Bain visited 17 farms in Brown County to examine animals.
Once the fair begins, he or another veterinarian will conduct a quick inspection of each animal to make sure it is still well and that the health papers are in order.
The exams are to protect the owners of livestock and to protect the public, he said.
"I would not worry about petting the animals at the fair," he said. "They have been examined, and they are very clean. The owners wash them continually."
Daniel Sharp , a 4-H member from Bath who will be showing a Brown Swiss dairy heifer at the Brown County Fair, said he washes and grooms his animal frequently. He works with his heifer daily, putting her through a mock show so she will earn high marks at the fair. He knows when she is feeling well or not, he said.
His heifer as well as other animals that he and his brother Travis Sharp will show at the fair were examined by a veterinarian on Friday and are in good shape, said Gretchen Sharp , the boys' mother and a 4-H leader.
Daly said that the inspection system "takes out a huge chunk of worry," but there is still a possibility that an animal might get sick after the fair has begun.
"That is what we have in Indiana at some of their fairs," he said.
The 4-H members showing animals should be aware of their animals' health before and during the fair. An animal that begins to eat less, is tired or feverish should be brought to the attention of an adviser or fair official, he said.
"We are always monitoring the health of the animals throughout the show," Gretchen Sharp said. "If they get sick, we take them home right away."
Public health officials say fairgoers should wash their hands with soap and water or use hand sanitizer after petting animals.
Daly said petting animals, even pigs, is permissible.
"I would hate to make a blanket statement that people shouldn't pet the pigs because of the possibility of H3N2v," he said. "Petting animals is what fairs are for. Parents should just keep track of what their kids are doing and make sure they wash their hands before leaving the barn or before eating."
Becca Wolff , 4-H youth adviser in Brown County, said entries are up for livestock exhibits this year. There are 475 entries in the categories of beef, swine, dairy cow, dairy goat, meat goat, poultry, rabbits, dogs and cats.
Livestock will be checked in on Wednesday and the shows will run Thursday through Saturday.
She said she encourages people to come out to the barns and see the animals.
"I think the livestock is the foundation of the fair," she said. "It was what the fair was built on. It is a chance for people in town to experience animals and a chance for producers to show their quality livestock."