UPDATE 2-USDA finds more show pigs with H1N1 flu virus

* Six pigs from Minnesota fair test positive for virus

* Samples from six additional pigs being retested

* USDA assures consumers pork is safe

* Chinese signals it will lift ban on U.S. pork

* Mexican farmers want border shut to U.S. pork imports (Adds details and background, comment from Mexico pork producers group)

WASHINGTON, Oct 29 - Six pigs shown at the Minnesota State Fair last month have been confirmed as having had the pandemic H1N1 flu virus, the U.S. Agriculture Department said on Thursday.

The USDA said it is running confirmatory tests on samples from another six pigs that tested positive for the virus during preliminary tests. Some of those samples were collected at the South Dakota State Fair, the USDA said.

"People cannot get this flu from eating pork or pork products," the USDA said in a memo about the results.

The USDA found the virus in the first U.S. hog on Oct. 19 -- one of the six positives from the Minnesota State Fair.

The virus, which infected as many as 5.7 million Americans between April and July, is commonly called swine flu. ID:nN29365484

The swine samples were taken as part of a research project that documents flu viruses in settings where people and hogs interact. ID:nN19386595

The project, funded by the U.S. Centers for Disease Control and Prevention, tested 57 samples from pigs at the Minnesota fair and 45 samples from the South Dakota fair.

There are no plans to conduct further tests on the samples that were negative for the flu, the USDA said.

The USDA said hog producers need to guard against the spread of the flu in hogs from people who are sick with the virus. Flu viruses, which are airborne, can pass back and forth between people and pigs.

The new strain of H1N1 virus, which has genetics from humans, birds and swine, likely circulated undetected in pigs for at least a decade before jumping to humans, according to an expert at the University of Arizona. ID:nN1527435

The USDA, which is working with manufacturers to speed the development of an H1N1 vaccine for hogs, said it plans to post all future suspected cases of the virus in hogs at www.usda.gov/H1N1flu

The virus has been reported in hogs in Canada, and turkeys in Canada and Chile. ID:nN20444317

VIRUS HAS HELPED DEPRESS US HOG MARKET

Trade bans sparked by the outbreak have weighed on hog markets.

China had banned U.S. pork since May because of the outbreak in humans, but Chinese officials said on Thursday they plan to lift the ban. ID:nN29341577

World trade bodies have said there is no reason to restrict pork trade because of the virus.

Mexican pork producers said they want their government to ban imports of U.S. pork because of the new H1N1 findings. The Mexican government said it could not comment on potential trade actions.

"We are asking that they close the border until this situation in Minnesota is cleared up," said Enrique Dominguez, the head of the Mexican pork producers association, in an interview with Reuters.

Mexico imports 470,000 tonnes of pork from the United States each year and produces about 1.2 million tonnes, Dominguez said.