Ag News

Screwworm spread prompts ban of Mexican livestock imports

On May 11, the USDA announced it is suspending the import of live cattle, horse, and bison through U.S. ports of entry along the southern border due to the continued and rapid northward spread of New World Screwworm (NWS) in Mexico, effective immediately. NWS has been recently detected in remote farms with minimal cattle movement as far north as Oaxaca and Veracruz, about 700 miles away from the U.S. border.

The United States and Mexico continue efforts to prevent the further spread of and eradicate NWS in Mexico. 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.

This import suspension will persist on a month-by-month basis, until a significant window of containment is achieved. USDA will continue constant collaboration with Mexico, including a review of latest data and metrics in two weeks. Any livestock currently in holding for entry into the United States will be processed normally; this includes an Animal and Plant Health Inspection Service (APHIS) port Veterinary Medical Officer inspection exam and treatment to ensure they are not carrying NWS.

“The protection of our animals and safety of our nation’s food supply is a national security issue of the utmost importance,” said Agriculture Secretary Brooke Rollins. “Once we see increased surveillance and eradication efforts, and the positive results of those actions, we remain committed to opening the border for livestock trade. This is not about politics or punishment of Mexico, rather it is about food and animal safety.”

Effective eradication requires a three-pronged approach: robust active field surveillance with education and outreach to ensure prevention, treatment, and early detection; controlled animal movement to limit spread; and sustained sterile insect dispersal.

Suspending livestock transport through southern ports of entry will assist in the effort to limit northbound transport of NWS through livestock commerce, and will allow the U.S. to reassess whether current mitigation standards remain sufficient.

It is important to note the northward spread of NWS is possible through natural wildlife movements, including wildlife that transit the border region without impediment.

USDA is taking all possible actions to monitor for, and limit, the northward movement of NWS, including the utilization of the USDA Tick Riders to monitor livestock and wildlife along the southern border region, between the ports of entry, for the presence of NWS.

The U.S. previously and successfully led the eradication of NWS in the U.S. and Mexico, however, this cost billions of dollars and took decades. Unfortunately, these recent detections in Mexico show that this dangerous pest is back and remains a serious threat to the health of U.S. animals, its food supply, and security.

The first case of NWS in Mexico was reported to the U.S. in November 2024. When NWS fly larvae (maggots) burrow into the flesh of a living animal, they cause serious, often deadly damage to the animal. NWS can infest livestock, pets, wildlife, occasionally birds, and in rare cases, people.

In November 2024, after a positive detection of NWS in southern Mexico, USDA shut down the border for live animal trade.

In February 2025, USDA resumed imports after APHIS and Mexico agreed to and implemented a comprehensive pre-clearance inspection and treatment protocol to ensure safe movement and steps to mitigate the threat of NWS.

Over the last two years, screwworm has spread north throughout Panama and into Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador, Belize and now Mexico.

APHIS is releasing sterile flies through aerial and ground release at strategic locations, focusing on Southern Mexico and other areas throughout Central America. A complete list of regions APHIS recognizes as affected by NWS as well as more detailed information on trade restrictions can be found on the USDA APHIS Animal Health Status of Regions website.

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