The US Department of Agriculture has suspended the transport of live cattle, horses and bison through ports of entry along the border with Mexico for at least two weeks. It’s part of an effort to curb the spread of New World screwworm, a flesh-burrowing larva that can be fatal to animals and devastate cattle herds.
The parasite was detected in Mexican farms as far north as Oaxaca and Veracruz, roughly 700 miles from the US border.
“The protection of our animals and safety of our nation’s food supply is a national security issue of the utmost importance,” Secretary of Agriculture Brooke L. Rollins said in a statement Sunday. “This is not about politics or punishment of Mexico, rather it is about food and animal safety.”
Mexican Agriculture Secretary Julio Berdegué said on X that he had spoken with Rollins, who informed him of the decision.
“We don’t agree with this measure, but we’re confident we’ll reach an agreement sooner rather than later,” Berdegué said.
Mexican President Claudia Sheinbaum also expressed discontent over the US’s decision, describing it as “unfair” amid tariffs imposed on other goods.
“We do not agree with this measure,” Sheinbaum said Monday. “The Mexican government has been working on all fronts from the very first moment we were alerted to the screwworm.”
The US had shut down the border for live animal trade from Mexico in November after screwworms were detected in the southern part of the country, then lifted the ban in February when measures were put in place to evaluate animals before they entered the US.
The new import suspension will be reviewed on a “month-by-month” basis until there is demonstrated containment, USDA said.
“Secretary Berdegué and I have worked closely on the NWS response; however, it is my duty to take all steps within my control to protect the livestock industry in the United States from this devastating pest,” Rollins said.
Screwworm flies lay eggs in the open wounds or orifices of warm-blooded animals. These fly larvae, the screwworms or maggots, burrow into the flesh of the animal, which can cause serious damage, leading to infections and death in some instances.
Although it primarily affects livestock, it can infest people, according to the US Centers for Disease Control and Prevention. Infestations are painful, and the larvae may be visible in a wound. In April, Mexico’s Health Ministry confirmed the country’s first human case of screwworm in a 77-year-old woman in the southern state of Chiapas. She received antibiotic treatment for the infection and remained in stable condition.
Screwworm was declared eradicated in the US in 1966, but an outbreak in 1972 resulted in tens of thousands of cases in livestock across multiple Southern states. Texas alone found 90,000 cases, after reporting 444 the previous year. Since 1982, only a handful of cases have been documented, most notably in 2016 in the Florida Keys, when screwworm infected a deer population.
Over the past two years, screwworm has spread north from countries such as Panama, Costa Rica, Nicaragua, El Salvador, Guatemala, Belize and now Mexico, the USDA said.
“The United States and Mexico continue efforts to interdict and eradicate NWS in Mexico and work in good faith,” the USDA said. “However, despite these efforts and the economic impact on both countries due to this action, there has been unacceptable northward advancement of NWS and additional action must be taken to slow the northern progression of this deadly parasitic fly.”
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