Health officials are making a renewed call for vigilance against bird flu, but some experts are puzzling over why reports of new human cases have stopped.

The first major global review of bird flu in cats reveals an emerging threat of a potential human pandemic. Spring is here, birds are on the move, and a new threat is spreading alongside them: bird flu (H5N1).

Bird flu has killed over 166 million birds worldwide and is now spreading to other animals, including cows, and more concerningly, cats.