The flesh-eating livestock pest New World screwworm has advanced closer to the U.S. border with Mexico, the U.S. Department of Agriculture said, prompting Washington to block imports of Mexican cattle just days after it allowed them to resume at a port of entry in Arizona.

Animal health worker Eduardo Lugo treats the wounds of a cow as Chihuahua ranchers intensify surveillance for the screwworm after the U.S. suspended cattle imports following the detection of the parasite in southern Mexico,