KANSAS CITY (Reuters) - Humans have it. Pigs don't. At least not yet, and U.S. pork producers are doing everything they can to make sure that the new H1N1 virus, known around the world as the "swine flu," stays out of their herds.

"That is the biggest concern, that your herd could somehow contract this illness from an infected person," said Kansas hog farmer Ron Suther, who is banning visitors from his sow barns and requiring maintenance workers, delivery men and other strangers to report on recent travels and any illness before they step foot on his property.

"If a person is sick, we don't want you coming anywhere on the farm," Suther said.

"There is no evidence of this new strain being in our pig populations in the United States. And our concern very much is we don't want a sick human to come into our barns and transmit this new virus to our pigs," said National Pork Producers chief veterinarian Jennifer Greiner.

"If humans give it to pigs, we don't have things like Tamiflu for pigs. We don't have antivirals. We have no treatment other than to give them aspirin," said Greiner.

The World Health Organization on Thursday officially declared it would stop calling the new strain of flu "swine flu," because no pigs in any country have been determined to have the illness and the origination of the strain has not been determined.

The never-before-seen H1N1 flu virus has elements of swine, avian and human varieties.

PIGS BEHIND SECURITY FENCES

Still, U.S. hog farmers said flu fears have hit them hard in the wallet as hog prices plummeted this week in response. Many countries reacted to the outbreak earlier this week by banning pork or meat from U.S. states that have human cases of the flu. And Egypt ordered the slaughter of all pigs in the country as a precaution.

U.S. hog producers have already been struggling financially for more than a year due to poor prices and high feed costs. If the new flu strain does hit their herds, it could spur further price declines, and could potentially spread broadly through herds.

To try to protect against such a scenario, industry groups and veterinarians this week warned farmers to step up their biosafety protocols, keeping pigs in barns behind security fences with access by any outsiders extremely limited.

Purdue University veterinarian Sandy Amass said farmers should keep an eye on pigs for "coughing, runny nose, fever and a reduction in feed intake," and to have the animals tested immediately if they exhibit such flu symptoms.

"Pigs get flu just like people get flu," Amass said. "We're want to do everything possible so the pigs don't get infected."

For Carroll, Iowa, producer Craig Rowles that means if any of his workers feel sick, they are ordered to take time off work -- paid -- to keep them away from the pigs.

"It's a real issue," Rowles said. "If the pigs get it, there isn't much we can do. Water, aspirin, and bed rest, that's all we've got."