Originally published on September 22, 2025 on RealAgriculture by RealAgriculture Livestock Team.
Mexico has confirmed a new case of new world screwworm less than 70 miles (113 km) from the U.S. border near Sabinas Hidalgo, located in the state of Nuevo León.
New world screwworm (NWS) is a livestock pest that feeds on live tissue of livestock and even humans. It causes large, festering wounds, and can cause infection, sepsis and death. The pest was eradicated from the U.S. in 1966, using a combination of detection, treatment, and sterile male fly releases, that pushed the range of the pest south into South America.
This latest detection is the northernmost of the current NWS outbreak that began November 2024, and the one most threatening to the American cattle and livestock industry. Sabinas Hidalgo is located near the major highway from Monterrey, Nuevo Leon, to Laredo, Texas, which is one of the most heavily trafficked commercial thoroughfares in the world, says the U.S. Department of Agriculture. The last detection was July 9 in Veracruz, about 590 km further south.
Preliminary reports Mexican authorities indicate that the affected animal, an 8-month-old calf, had been moved to a certified feedlot in Nuevo León from a region in southern Mexico with known active NWS cases. USDA says it is analyzing all new information related to this case at Nuevo León and will “pursue all options to release sterile flies in this region as necessary.”
The U.S. had previously closed the U.S-Mexico border to cattle, horse and other animal movement to mitigate the risk of bringing new world screwworm into the country. Plans to re-open cattle movement in stages were cancelled May 11 with a posted detection in Mexico.
Since July, USDA alongside Mexico, has been monitoring nearly 8,000 traps across Texas, Arizona, and New Mexico. To date, more than 13,000 screening samples have been submitted, with no NWS flies detected.
In a press release Sunday, U.S. ag secretary Brooke Rollins calls the protection of the U.S. from new world screwworm a national security priority and that the administration is continuing with its 5-pronged approach to controlling the pest.
The ag secretary also took aim at Mexico, saying, “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. 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.”
The potential link to animal movement underscores the non-negotiable need for Mexico to fully implement and comply with the U.S.–Mexico Joint Action Plan for NWS in Mexico, the USDA says.
As of Sept. 22, U.S. ports remain closed to imports of cattle, bison, and horses from Mexico.
USDA says it plans to release a “significant plan” to help rebuild the American cattle supply.
