Screwworm threat forces US to halt cattle imports from Mexico

Yahoo

12-05-2025

U.S. Agriculture Secretary Brooke Rollins said she is suspending imports of livestock through the Mexican border on a "month-by-month basis" to protect U.S. cattle from the threat of a dangerous, flesh-eating parasite infestation.
The parasite is the New World Screwworm, or NWS, which is actually a fly and was eradicated in the U.S. almost 60 years ago. The Agriculture Department said in a statement May 11 that NWS was recently detected in remote Mexican farms within 700 miles of the U.S. border. The statement cited "unacceptable northward advancement of NWS" and said additional action must be taken.
"Due to the threat of New World Screwworm I am announcing the suspension of live cattle, horse and bison imports through U.S. southern border ports of entry effective immediately," Rollins said in a social media post. "The last time this devastating pest invaded America, it took 30 years for our cattle industry to recover. This cannot happen again."
Mexico's agricultural council chief, Luis Fernando Haro, said the ban is unnecessary and "does not the solve the problem." He said established protocols already ensure that cattle crossing into the U.S. are "guaranteed to be free of screwworms." Mexican Agriculture Secretary Julio Berdegue said he disagreed with the ban but hoped the two countries would reach an agreement soon.
Rollins called the protection of U.S. animals and the safety of the nation's food supply "a national security issue of the utmost importance." When increased surveillance and eradication efforts begin showing positive results, the border will reopen for livestock trade, she said.
"This is not about politics or punishment of Mexico, rather it is about food and animal safety," Rollins said.
The Agriculture Department eradicated the NWS parasite in 1966 by releasing sterile male flies and pupae to eventually lead to infertile screwworm flies, according to the USDA's Animal and Plant Health Inspection Service.
In November 2024, America halted imports of Mexican livestock after the country alerted the U.S. to a NWS detection in a cow at an inspection checkpoint close to the Mexico border with Guatemala. Subsequently, the USDA increased sterile fly deliveries and supported additional surveillance programs, which led to livestock imports restarting in February this year.
Relations became strained last month, however, when Mexico authorities began curtailing seven-day flights of USDA planes dispersing sterile flies and imposing import duties on "critical aviation parts, dispersal equipment and sterile fly shipments," Rollins said in a letter to Esteban Moctezuma Barragán, Mexico's ambassador to the U.S.
Mexico temporarily avoided the ban by reaching a deal to allow additional flights and waive custom duties.
The parasite gets its name from how the larvae's resulting maggots, which as they feed on an animal will burrow, or screw, into a wound or opening, creating "extensive damage by tearing at the hosts' tissue with sharp mouth hooks," USDA's Animal and Plant Health Inspection Service says.
Adult screwworm flies are similar to – or slightly larger than – the common housefly, but they have orange eyes, a metallic blue or green body and three dark stripes along their backs.
NWS does not regularly occur or spread in the United States but is typically found in South America and the Caribbean. People who travel to these areas, spend time among livestock animals, sleep outdoors and have an open wound are at greater risk of becoming infected with NWS.
This article originally appeared on USA TODAY: Screwworm threat forces US to halt cattle imports from Mexico