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.

The reemergence of the New World screwworm, which poses significant health risks for livestock, has prompted the Department of Agriculture to halt cattle shipments from Mexico to the United States. The move marks at least the second time this year that cattle imports from Mexico have been suspended over the parasitic fly.

The U.S. closes its southern border due to New World screwworm fly, a flesh-eating parasite that has decimated cattle ranches in the past.