The U.S. Department of Agriculture has identified the first infection of a virulent strain of avian flu in poultry in Kansas, confirming the virus has spread into a migratory bird route that runs through the center of the country. The discovery of the H5N2 flu strain in a backyard chicken and duck flock in a county just outside Kansas City, Kan., is certain to lead to expanded restrictions on U.S. poultry exports from top trading partners like Mexico and Canada.