Starting Monday, the United States will begin gradually reopening cattle imports from Mexico after a two-month suspension due to concerns over the spread of the screwworm, a dangerous livestock parasite.
The worms are parasitic larvae of the Cochliomyia hominivorax fly. Female flies lay their eggs in wounds or mucous membranes of warm-blooded animals, including humans, and those larvae then burrow into the animal. The larvae use tiny hooks in their mouths to eat the flesh of their victim and if that infestation is left untreated, an adult cow can die from it in just a few weeks.
The US Department of Agriculture (USDA) halted animal imports from Mexico on May 11 after detecting the presence of the screwworm, a fly species capable of infesting livestock by burrowing maggots into tissue and eating its flesh. Though previously eradicated in the US for decades, the screwworm has been moving northward in Mexico.
Concerns were raised about the flies in 2024 after an outbreak was discovered in southern Mexico. Imports were restricted in November, then lifted in February before the screwworm made "unacceptable northward advancement" and the ban was implemented in May. Rollins said at the time "The protection of our animals and safety of our nation's food supply is a national security issue of the utmost importance."
The USDA announced that the first port to resume operations will be in Douglas, Arizona. The agency said this location poses the lowest risk due to its geographic position and its “long history of effective collaboration” with officials in Sonora, Mexico.
To support containment efforts, the USDA announced last month it would open a new sterile fly dispersal facility in Texas and invest $21 million to update a similar plant in Mexico. That facility will distribute sterile flies that are grown in Panama. No sterile fly factory exists right now in the United States.
USDA Secretary Brooke Rollins confirmed the phased plan in a public statement, highlighting efforts by the Trump administration to contain the pest.
“At USDA we are focused on fighting the New World Screwworm’s advancement in Mexico. We have made good progress with our counterparts in Mexico to increase vital pest surveillance efforts and have boosted sterile fly dispersal efforts. These quick actions by the Trump Administration have improved the conditions to allow the phased reopening of select ports on the Southern Border to livestock trade,” Rollins said. “We are continuing our posture of increased vigilance and will not rest until we are sure this devastating pest will not harm American ranchers.”
After Douglas, Arizona, additional ports will reopen on a set schedule: Columbus, New Mexico, on July 14; Santa Teresa, New Mexico, on July 21; Del Rio, Texas, on August 18; and Laredo, Texas, on September 15. The USDA said it will monitor conditions after each reopening to ensure its control measures are effective.
According to Reuters, Mexico has been trying to convince the USDA to accelerate these re-openings, also confirming it will ban the movement of livestock without proof of inspection and treatment.
