KANSAS CITY, Mo. – Shares in major poultry processors retreated on news that highly pathogenic H5N2 avian influenza was confirmed in Missouri and Arkansas.

Shares in Tyson Foods Inc., which is based in Springdale, Ark., dropped $2.23 to $37.55. Investor.com reported that Tyson, the world's second-largest meat and poultry processor, closed as the worst performer on the S&P 500 on March 11.

“No flocks grown for Tyson Foods have been diagnosed with avian influenza,” Worth Sparkman, manager of public relations, told meatpoultry.com. “There are always biosecurity measures in place on poultry farms and we've been even more diligent since AI has been in the US this winter.”

Meanwhile, shares in Greeley, Colo.-based Pilgrim's Pride Corp. declined 4 percent to $25.36. Pilgrim's is a unit of JBS SA. Sanderson Farms, Inc., Laurel, Miss., registered a 5.7 percent drop to $77.85 after slipping more than 1.75 percent in after-hours trading.

As part of an announcement of a site for the company's new poultry processing complex, Joe F. Sanderson, chairman and CEO, noted that none of the company's flocks have been affected by the virus.

“Avian influenza has not been identified in any of the states in which we have operations and live inventory,” Sanderson said. “However, we have taken this opportunity to remind all of our contract poultry producers and our employees that the Company requires strict adherence to its biosecurity program, and have reminded them of the program’s specific requirements and procedures. Consistent with standard industry practice, all of our flocks are tested for avian influenza before they are processed.”

The Arkansas Livestock and Poultry Commission reported that H5N2 avian flu was confirmed at a commercial turkey farm in Boone County, Ark. Samples were taken from the birds and sent to the state veterinary diagnostic lab for tests. The samples tested positive for H5N2 and were then sent to the National Veterinary Services Lab (NVSL) of the US Department of Agriculture. NVSL confirmed the presence of H5N2.

The Missouri Department of Agriculture confirmed the presence of H5N2 at two turkey facilities. State agriculture officials quarantined both farms and culled more than 40,000 turkeys.