CHICAGO (Reuters) -The U.S. Department of Agriculture announced on Monday a phased reopening of cattle, bison and equine imports from Mexico following a prolonged closure over the damaging pest New World screwworm.

Ports will reopen in phases as early as July 7, beginning with Douglas, Arizona, which the USDA said is the lowest risk entry point due to its location and the "long history of effective collaboration" between officials in Sonora and USDA's Animal and Plant Health Inspection Service.

The southern U.S. border was closed to imports of the animals on May 11 after screwworm, a species of fly that has been eradicated in the U.S. for decades, had been moving northward in Mexico. Additional ports in New Mexico and Texas may be reopened in coming weeks.

The pest can infest livestock and wildlife and carry maggots that burrow into the skin of living animals, causing serious and often fatal damage.

As part of the country's effort to fight screwworm encroachment, the USDA announced plans on June 18 to open a sterile fly dispersal facility in Texas, and invested $21 million in updating a plant in Mexico to produce sterile flies.

"We have made good progress with our counterparts in Mexico to increase vital pest surveillance efforts and have boosted sterile fly dispersal efforts," USDA Secretary Brooke Rollins said in a release.

"We are continuing our posture of increased vigilance and will not rest until we are sure this devastating pest will not harm American ranchers," she said.

The port in Columbus, New Mexico, may reopen on July 14, followed by Santa Teresa, New Mexico, on July 21, Del Rio, Texas, on August 18 and Laredo, Texas, on September 15, the USDA said. The agency added that it will evaluate conditions after each reopening to ensure that the enhanced control measures are working.