Mexican President Reacts to US Southern Border Shutting Down Following Screwworm Threat

Mexican President Claudia Sheinbaum criticized the United States’ decision to shut down the U.S.–Mexico border following the detection of a new incidence of New World screwworm (NWS) flesh-eating pests.

“From our point of view, it is a totally exaggerated decision to close the border again,” Sheinbaum said during a Thursday morning press conference.

U.S. Agriculture Secretary Brooke Rollins announced the closure of livestock trade through southern ports of entry on Wednesday, with the shutdown “effective immediately,” according to a July 9 statement from the Department of Agriculture (USDA).

The decision to close the ports was taken after Mexico reported a new case of NWS on July 8 in the Ixhuatlan de Madero region in the state of Veracruz, roughly 370 miles south of the U.S.–Mexico border.

“This new northward detection comes approximately two months after northern detections were reported in Oaxaca and Veracruz, less than 700 miles away from the U.S. border, which triggered the closure of our ports to Mexican cattle, bison, and horses on May 11, 2025,” said the statement.

On June 30, the USDA announced a phased reopening of the five closed ports between July 7 and Sept. 15. However, the latest report of NWS closer to the U.S. border “severely compromises the outlined port reopening schedule of five ports,” the USDA said.

The United States has said it would be vigilant, and after a new NWS case was detected, the USDA paused the port reopening to quarantine the pest, Rollins said.

“We must see additional progress combating NWS in Veracruz and other nearby Mexican states in order to reopen livestock ports along the Southern border,” she said.

Rollins credited “aggressive monitoring” by USDA staff for ensuring America was able to take decisive action against NWS.

NWS is a “devastating pest that causes serious and often deadly damage to livestock, wildlife, pets, and in rare cases, humans,” according to the USDA.

NWS females lay eggs on wounds or orifices of warm-blooded animals. The larvae that hatch from these eggs burrow deep into the wound, feeding off the flesh. The wound keeps growing as more maggots hatch and feed, eventually becoming severe enough to kill the host animal.

A single female NWS fly is capable of laying up to 3,000 eggs during its lifespan. As such, a large infestation of these flesh-eating parasites poses a significant risk to farmers raising animals such as sheep and cows.

In its July 9 statement, the USDA said it will “continue to have personnel perform site visits throughout Mexico to ensure the Mexican government has adequate protocols and surveillance in place to combat this pest effectively and efficiently.”

The United States plans to counter the NWS threat by using sterile male NWS flies. When such male flies are released en masse into an NWS swarm, they eventually mate with the wild females, who end up laying unfertilized eggs, thus bringing down the population.

At present, the United States can procure 100 million flies per week from a sterile fly production facility in Panama. The USDA has invested $21 million in another production facility in Mexico that can provide up to 100 million files per week when operational.

Last month, Rollins launched an $8.5 million sterile NWS fly dispersal site at Moore Air Base in South Texas.

Reuters contributed to this report.