(Updates with stock prices for poultry companies, background on bird flu)
CHICAGO, March 11 (Reuters) - The U.S. Department of Agriculture on Wednesday confirmed the discovery of highly pathogenic avian influenza in a commercial turkey flock in Arkansas, the third-largest U.S. turkey producer and home to Tyson Foods Inc, the nation's biggest chicken company.
Shares of Tyson and other poultry companies, including Pilgrim's Pride Corp and Sanderson Farms Inc, tumbled on concerns the discovery will further limit U.S. trade with Asia and Latin America.
Countries like Taiwan, Singapore and Nicaragua have already restricted poultry exports from states that have suffered bird flu outbreaks, including Minnesota, Missouri, California and Oregon.
Tyson's stock price was down 4.9 percent at $37.85 at 12:30 p.m. CDT (1730 GMT) after hitting a five-month low of $37.35. Pilgrim's Pride shares sank 7.3 percent, and Sanderson Farms shares lost 5.4 percent.
The infected flock of 40,020 turkeys in Boone County, Arkansas, is located within the Mississippi flyway, a migratory route along which the same strain of H5N2 bird flu was previously identified in Minnesota and Missouri.
Arkansas officials quarantined the affected premises and birds on the property will be culled to prevent the spread of the disease, according to USDA. Birds from the flock will not enter the food system.
Confirmation of the outbreak came after the USDA said on Tuesday said there was a suspected case of bird flu in Arkansas. (Reporting by Tom Polansek; Editing by Marguerita Choy)