New World screwworm detected less than 70 miles from the US-Mexico border

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A case of New World screwworm (NWS) has been confirmed in Mexico less than 70 miles from the border with the US, according to an announcement by the US Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS).¹ The case marks the northernmost detection of NWS amid the current outbreak, increasing concerns for the American cattle and livestock industry.

Mexico’s National Service of Agro-Alimentary Health, Safety, and Quality (SENASICA) detected the flesh-eating parasite on September 21 in Sabinas Hidalgo, Nuevo León. The city of Sabinas Hidalgo sits along a major highway from Monterrey, Nuevo León, to Laredo, Texas—one of the busiest trade routes in the world. On average, more than 18,500 trucks cross through the Laredo port every day, including more than 15,000 crossings through the World Trade Bridge.²

In its announcement, the USDA called the most recent detection the “most threatening to the American cattle and livestock industry.”¹

US Secretary of Agriculture Brooke L. Rollins said the USDA is moving ahead with a 5-pronged plan to protect the US border from NWS. The plan includes investing in new eradication technologies, building sterile fly production and dispersal facilities in Texas,³ increasing surveillance and detection efforts, increasing public awareness and education campaigns, and coordinating with Mexico and international partners to contain the parasite.

“USDA urges residents on the southern border to check their pets and livestock for signs of NWS,” the agency wrote in its announcement, encouraging pet caregivers and handlers to look for NWS signs in open wounds, body openings, genitalia, or the navel.¹

Related: US Department of Health and Human Services authorizes emergency use of animal drugs for New World screwworm⁴

“Look for draining or enlarging wounds and signs of discomfort. Also look for screwworm larvae (maggots) and eggs in or around body openings, such as the nose, ears, and genitalia or the navel of newborn animals. If you suspect your animal is infected with screwworm, contact your state animal health official or USDA area veterinarian immediately,” the USDA continued.¹

Before the most recent detection, the last northernmost case was confirmed in an 8-month-old cow on July 9, 2025, in Veracruz, which is located approximately 370 miles farther south. According to SENASICA, the affected animal had been recently moved to a certified feedlot in Nuevo León from a region in southern Mexico with active NWS cases.

As of now, US ports are closed to imports of cattle, bison, and horses from Mexico.

According to the USDA, the agency in collaboration with Mexico has been monitoring nearly 8000 traps throughout Texas, Arizona, and New Mexico, with more than 13,000 screening samples being submitted to date and no NWS flies detected.

“USDA is analyzing all new information related to the recent case in Nuevo León and will pursue all options to release sterile flies in this region as necessary,” the agency wrote.¹

References

1. Mexico Confirms Case of New World Screwworm in Nuevo Leon. US Department of Agriculture Animal and Plant Health Inspection Service. News release. September 21, 2025. Accessed September 22, 2025.
2. Economic Outlook Report. Laredo Chamber of Commerce. May 2024. Accessed September 22, 2025. https://laredochamber.com/wp-content/uploads/2024/10/202405-Vision.pdf?utm_source=chatgpt.com
3. Bautista-Alejandre A. Clinic center: USDA announces sterile fly facility at Texas base for screwworm eradication, and more. dvm360. July 9, 2025. Accessed September 22, 2025. https://www.dvm360.com/view/clinic-center-usda-announces-sterile-fly-facility-at-texas-base-for-screwworm-eradication-and-more
4. Bautista-Alejandre A. US Department of Health and Human Services authorizes emergency use of animal drugs for New World screwworm. dvm360. August 19, 2025. Accessed September 22, 2025. https://www.dvm360.com/view/us-department-of-health-and-human-services-authorizes-emergency-use-of-animal-drugs-for-new-world-screwworm