The US Department of Agriculture has issued an ultimatum to Mexico to take immediate action to combat a rapidly spreading livestock parasite or face a sweeping shutdown of live animal imports into the United States within two days.

Herding cattle in in Mexico. Image: Shutterstock.

In a letter sent Saturday and published to social media, US Agriculture Secretary Brooke Rollins warned her Mexican counterpart that unless Mexico moves decisively to eliminate bureaucratic barriers and intensify eradication efforts against the New World screwworm, the US will restrict imports of cattle, bison, and equine animals from Mexico beginning Wednesday, April 30.

Mexico is the largest supplier of imported cattle to the US, sending over 1.1 million head in 2020.

But the trade diminished dramatically in November last year when the US halted Mexican cattle and bison imports after a detection of New World screwworm in southern Mexico.

The ban was lifted in early February after Mexico implemented a new pre-clearance inspection and treatment protocol.

However, in her letter on Saturday, Secretary Rollins said the outbreak in Southern Mexico continues to expand, which she blames on Mexican aviation authorities placing restrictions on USDA flights and inhibiting control efforts.

She has put the Mexican government on notice to “act immediately”.

“Without resolution by April 30, @USDA will close American ports of entry to cattle, bison, and equine from Mexico to protect U.S. agriculture,” she wrote on Twitter/X:

As the New World Screwworm outbreak is escalating, Mexico must eliminate restrictions on USDA aircraft and waive customs duties on eradication equipment. These barriers critically impair our joint response.

Without resolution by April 30, @USDA will close American ports of entry… pic.twitter.com/SPeR5l3D7s

— Secretary Brooke Rollins (@SecRollins) April 26, 2025

The National Cattlemen’s Beef Association (NCBA) emphasised its strongdsupport for Secretary Rollins’ actions, saying the US has spent millions of dollars to eradicate New World screwworm from its borders in the 1960s but unfortunately are now facing the dangerous threat again.

“Screwworm is very destructive and could cost American producers millions of dollars a year if it reaches us,” NCBA President and Nebraska cattleman Buck Wehrbein said.

Mexican authorities had “failed to uphold their end of the agreement” by disrupting planes carrying these sterile male files, refusing pilots permission to land, and instituting customs duties on flight components, sterile flies, and sterile insect technique equipment.

“We have received multiple reports that critical flights carrying these sterile flies have been denied permission to land, faced bogus paperwork issues, and been charged high customs fees,” NCBA Senior Vice President of Government Affairs Ethan Lane said.

“As a result, we have lost significant time and investment that has allowed these dangerous pests to spread unchecked into southern Mexico.

“In light of those reports, NCBA met with the Mexican Embassy earlier this week to deliver the message that the Mexican government needs to be a partner on eradicating screwworms to protect both animal and human health. It’s time for Mexican authorities to act and we appreciate Secretary Rollins standing with American and Mexican cattle producers who want to see this pest stopped dead in its tracks.”

Mexican standoff

Despite the ultimatum, Mexico’s Secretary of Agriculture and Rural Development, Julio Berdegué, stated on social media on Sunday that Mexico will not “subordinate” itself to the United States’ warnings concerning the screwworm plague.

“As our president, Claudia Sheinbaum, has said, we act with a cool head; we collaborate, cooperate, but we never subordinate ourselves,” he said in a Twitter/X post.

At the same time he expressed confidence in reaching a favourable agreement.

He contestado puntualmente la carta de la secretaria de Agricultura de Estados Unidos Brooke Rollins, sobre el tema del gusano barrenador del ganado. Como ha dicho nuestra Presidenta @Claudiashein, actuamos con la cabeza fría, colaboramos, cooperamos, pero nunca nos subordinamos

— Julio Berdegué (@JulioBerdegue) April 27, 2025

Google translation:
I have promptly responded to the letter from U.S. Secretary of Agriculture Brooke Rollins regarding the cattle screwworm. As our President @Claudiashein has said, we act with a cool head, we collaborate, we cooperate, but we never submit.

A devastating pest

New World Screwworm. Image: Centre for Disease Control and Prevention.

The New World screwworm is a devastating pest, with larvae that burrow into the flesh of living animals, causing severe infections and sometimes death. Humans can also be infected.

The USDA has set a hard deadline of April 30 for Mexico to meet three key demands:

• Immediate operational aviation clearance for eradication flights
• Full waivers on all customs duties for emergency eradication materials
• Appointment of a senior-level liaison to expedite solutions

Secretary Rollins has also floated the idea of an emergency U.S.-Mexico summit of government leaders and technical experts to restore collaboration.

“Time is of the essence,” she warned in Saturday’s letter.

“Every delay in granting full operational authority and eliminating customs barriers undermines our collective ability to carry out this emergency response.

“We cannot afford to continue operating at partial strength.

“The situation requires immediate attention and decisive coordination at the highest levels of your Government.

“I must inform you that if these issues are not resolved by Wednesday, April 30, USDA will restrict the importation of animal commodities, which consist of live cattle, bison and equine originating from or transiting Mexico to protect the interests of the agriculture industry in the United States.”