Dairy cattle in Nevada have been infected with a new type of bird flu that’s different from the version that has spread in herds since last year. U.S. Agriculture Department officials announced the finding Wednesday. It indicates that distinct strains of the H5N1 bird fluvirus have spilled over from wild birds into cattle at least twice. Experts said it raises news questions about wider spread and the difficulty of controlling infections in animals and the people who work closely with them. The new virus version found in cattle has been linked to severe infections in the U.S. and Canada.