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).

During a call with U.S. doctors this month, one CDC official noted that there is a seasonality to bird flu: Cases peak in the fall and early winter, possibly due to the migration patterns of wild birds that are primary spreaders of the virus.

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