Routine blood tests conducted Friday on hens at Tyson Foods Inc., the world’s largest meat processor, led to the discovery of antibodies to the H7N3 strain of the bird flu. Therefore, on Tuesday the company decided to kill 15,000 hens believed to have been exposed to the virus.

“Even though the affected birds do not currently have the virus, the flock is being depopulated today as a precautionary measure and will not enter the human food chain. While the birds' exposure to this strain of avian influenza poses no risk to human health, USDA's policy is to eradicate all H5 and H7 subtypes,” the company, based in Springdale, Arkansas, said in a statement.

Jon Fitch, director of the state’s Livestock and Poultry Commission, sustained the same thing saying, “there is absolutely no human health threat. But we take this seriously,” the USA Today quoted him.

However, a 2004 outbreak of H7N3 at a poultry plant in British Columbia, Canada, infected two workers, the Centers for Disease Control and Prevention warns.

The deadly H5N1 strain of bird flu has spread to humans overseas who have been in close contact with infected chickens. According to the World Health Organization, there have been 382 human cases worldwide since 2003, 241 of them fatal. Indonesia is the hardest hit regions of all, with 108 of the deaths and is seen by health experts as a potential hotspot for a pandemic. Scientists have long warned that the H5N1 strain of bird flu virus could mutate into a form that spreads easily among humans, leading to a pandemic that would kill millions.

While the virus discovered at Tyson Foods is harmless to humans, shares of U.S. chicken companies dropped as investors worried foreign buyers may ban U.S. chicken. The U.S. exports about 16 percent of its chicken and a loss of key overseas markets could create a glut of chicken here.

Following the discovery, the U.S. Agriculture Department has already suspended shipments of chicken from Arkansas to Russia, the most important overseas market for U.S. chicken.

Moreover, stock in Tyson fell by 8 percent in trading Tuesday, down $1.47 to 16.98 per share.