Mexico detects screwworm near U.S. border, heightening threat to American livestock

MEXICO – The U.S. Department of Agriculture (USDA) confirmed on September 21 that Mexico has detected a new case of New World screwworm (NWS) in Sabinas Hidalgo, Nuevo León, less than 70 miles from the U.S.-Mexico border. 

The finding represents the northernmost detection of the pest during the current outbreak and poses the most direct threat yet to America’s cattle and livestock industry.

Sabinas Hidalgo lies on a major trade route connecting Monterrey, Nuevo León, to Laredo, Texas, one of the busiest commercial corridors in the world. The location underscores the risk of cross-border spread.

“Protecting the United States from NWS is non-negotiable and a top priority of the Trump Administration,” said U.S. Secretary of Agriculture Brooke Rollins. 

“This is a national security priority. We have given Mexico every opportunity and every resource necessary to counter NWS since announcing the NWS Bold Plan in June 2025. Nevertheless, American ranchers and families should know that we will not rely on Mexico to defend our industry, our food supply or our way of life.”

Threat intensifies as case moves north

The infected animal, an eight-month-old cow, had recently been transported to a certified feedlot in Nuevo León from southern Mexico, where active cases are ongoing. This link to animal movement highlights the need for strict adherence to the U.S.-Mexico Joint Action Plan to contain the pest.

The previous northernmost detection was reported in Veracruz on July 9, about 370 miles further south. U.S. ports remain closed to imports of cattle, bison, and horses from Mexico as a precautionary measure.

Since July, USDA and Mexican authorities have maintained nearly 8,000 surveillance traps across Texas, Arizona, and New Mexico. 

More than 13,000 samples have been screened with no NWS flies detected so far on U.S. soil. USDA is now evaluating options to disperse sterile flies in northern Mexico to halt the pest’s advance.

USDA’s five-pronged plan

Under Rollins’ leadership, USDA has rolled out a sweeping five-pronged plan to counter the threat. The strategy includes major investments in technology, expanded sterile fly production, enhanced surveillance, border protections, and intensive coordination with Mexican authorities.

Key measures include the construction of a sterile fly dispersal facility at Moore Air Force Base in Edinburg, Texas, and plans for a production facility capable of releasing 300 million sterile flies weekly. 

Meanwhile, USDA continues to distribute 100 million sterile flies per week in Mexico and is helping expand production at a facility in Metapa.

The agency is also spearheading the US$100 million NWS Grand Challenge to develop breakthrough tools such as advanced traps, genetic engineering methods, and new sterilisation technologies.

Uniting federal partners

USDA is leading an unprecedented interagency response, with support from the Centers for Disease Control and Prevention, the Food and Drug Administration, the Department of the Interior, the Department of Homeland Security, and others. 

Together, these agencies are working under the U.S. One Health Coordination Unit for NWS to strengthen surveillance, expedite emergency approvals, and train personnel along the southern border.

Screwworm maggots burrow into wounds of livestock, wildlife, and even humans, feeding on living tissue. USDA is urging livestock owners in southern states to inspect animals for suspicious wounds closely and to report possible cases immediately.

While human cases are rare, health officials advise anyone with unusual skin lesions to seek medical attention without delay.

As Rollins emphasised, “We are firmly executing our five-pronged plan and will take decisive action to protect our borders, even in the absence of cooperation. Furthermore, we will pursue aggressive measures against anyone who harms American livestock.”

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