APHIS halts live animal imports across US southern border again due to screwworm
Updated May 23, 2025
The U.S. Department of Agriculture (USDA) announced May 11 the suspension of cattle, horse, and bison imports through ports of entry along the southern border due to the rapid northward spread of New World screwworm (NWS) in Mexico, effective immediately.
Despite continued efforts by the U.S. and Mexico to stop the spread of NWS and eradicate it from Mexico, the flesh-eating parasitic fly has been recently detected in remote farms with minimal cattle movement as far north as Oaxaca and Veracruz, about 700 miles from the U.S. border, according to the USDA announcement.
USDA’s Animal and Plant Health Inspection Service (APHIS), in conjunction with Customs and Border Protection (CBP), temporarily suspended livestock imports from Mexico after the latter detected NWS in November 2024. The ban was lifted in February after the U.S. and Mexico agreed to implement a preclearance inspection and treatment protocol to mitigate the threat of NWS.
However, that collaboration became strained in April when Mexican authorities began limiting flights of USDA planes dispersing sterile flies from seven to six days a week and imposing import duties on “critical aviation parts, dispersal equipment, and sterile fly shipments,” U.S. Agriculture Secretary Brooke Rollins said in an April 26 letter to Esteban Moctezuma Barragán, Mexico's ambassador to the U.S.
The Panama-United States Commission for the Eradication and Prevention of Screwworm (COPEG), a joint program between APHIS International Services and Panama’s Ministry of Agricultural Development, also releases sterile flies at strategic locations to disrupt reproduction, focusing on Southern Mexico and other areas throughout Central America.
“Time is of the essence. Every delay in granting full operational authority and eliminating customs barriers undermines our collective ability to carry out this emergency response. We cannot afford to continue operating at partial strength,” she wrote.
Mexico responded to Secretary Rollin’s letter and agreement was reached by April 30, but then further spread closed the border down again.
USDA indicated this most recent import suspension will continue 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 U.S. will be processed normally, which includes an APHIS port veterinary medical officer inspection and treatment to ensure the animal is not carrying NWS.
These restrictions also apply to dogs that may travel with their owners to Mexico and will require a health attestation before they are allowed to return to the U.S.
Over the last two years, NWS has spread north throughout Panama and into Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador, Belize, and now Mexico.
The NWS fly, Cochliomyia hominivorax, is a species of parasitic fly whose tissue-eating larvae can infest any living mammal and cause severe damage, infection, and often death.
A new fact sheet, “New World Screwworm: What You Need to Know ” from the U.S. Department of Agriculture (USDA) covers what to look for and how to report NWS infestation.
USDA’s National Veterinary Accreditation Program also has developed the training module, “Module 41: New World Screwworm: A 21st Century Perspective.” It goes over signs of NWS, its life cycle, control measures, and reporting methods. The presentation, released in early April, also covers the potential animal, human, and financial impacts associated with an incursion of NWS.
In addition, the AVMA has created a resource page on the New World screwworm, including information about its changing geographic distribution, how NWS infestation is treated, and what can be done to prevent its spread.