The U.S. Reinforces Livestock Import Ban Amid New Screwworm Threat

The U.S. has once again closed its southern border to livestock imports due to the alarming spread of the New World screwworm fly, a flesh-eating parasite that has advanced further north in Mexico than previously anticipated.

Mexican Leadership Responds

In response to the closure, Mexican President Claudia Sheinbaum voiced her criticism on Thursday, suggesting that the U.S. is overstating the risk posed to its beef industry by this parasite. The New World screwworm is particularly concerning as female flies lay eggs in the wounds of warm-blooded animals, giving rise to larvae that consume live flesh and fluids—an unusual feeding behavior among flies, which typically target dead material.

Economic Concerns

U.S. officials express significant concern that if the screwworm fly were to reach Texas, it could lead to substantial economic losses, reminiscent of the outbreaks experienced in the 1970s. Back then, the U.S. successfully eradicated the pest through a program involving the breeding and release of sterile male flies, but the organism has recently resurfaced in southern Mexico after being contained in Panama for years.

Recent Developments

Initially, the U.S. closed its southern border in May, prohibiting imports of live cattle, horses, and bison. Although three ports were scheduled to reopen this month and an additional two by September 15, an alarming infestation was reported 185 miles northeast of Mexico City—farther north than previously recorded, now approximately 370 miles from the Texas border.

Official Statements

U.S. Department of Agriculture Secretary Brooke Rollins affirmed the government’s commitment to safeguarding public health and the agricultural economy. “The United States has promised to be vigilant,” she stated. “Thanks to the aggressive monitoring by USDA staff, we have been able to take quick and decisive action to respond to the spread of this deadly pest.”

Mexico’s Countermeasures

Meanwhile, President Sheinbaum emphasized that Mexican authorities are adhering to all necessary protocols in handling the situation. Mexican reports indicate that there are currently 392 infected animals, marking a nearly 19% decrease since June 24.

Future Plans

Three weeks prior, Rollins unveiled a $30 million plan to combat the screwworm fly, which includes establishing new sites for breeding and dispersing sterile male flies. These males will mate with females in the wild, resulting in unviable eggs and ultimately reducing the fly population. Plans are in place for a new fly factory to begin operations in southern Mexico by July 2026, complementing an existing facility in Panama. Additionally, a site in southern Texas is set to be opened for holding the sterile flies imported from Panama for potential release.

Legislative Action

U.S. Representatives Tony Gonzalez of Texas and Kat McCammack of Florida have urged the Biden administration to quickly approve existing anti-parasite treatments for screwworm fly infestations in livestock, pointing out that current labeling requirements are hindering prompt action.