The United States has reclosed its southern border to livestock imports following the detection of the New World screwworm fly, a concerning flesh-eating parasite, significantly further north in Mexico. This move, aimed at protecting the U.S. livestock industry, comes after the parasite, previously eradicated in the U.S. in the 1970s, has shown a troubling spread.
The New World screwworm fly is known for its larvae that feed on the living flesh of warm-blooded animals, posing a severe threat to cattle, horses, and bison. While the U.S. had achieved eradication decades ago through a successful program involving sterile male flies, the recent discovery of infestations closer to the U.S. border, approximately 370 miles from Texas, has prompted renewed concern and decisive action.
U.S. Department of Agriculture (USDA) officials emphasize the necessity of these measures, citing aggressive monitoring efforts that revealed the parasite’s northward progression. The USDA is committing nearly $30 million to enhance control strategies, including establishing new facilities for breeding and releasing sterile male flies. This method aims to disrupt the parasite’s reproductive cycle and prevent viable offspring, thereby reducing the population. A new fly factory in southern Mexico is anticipated to be operational by July 2026 to bolster these efforts.
Mexican authorities, however, have voiced criticism of the U.S. decision, with Mexico’s President describing it as “totally exaggerated.” They report a decrease in infected animals within Mexico and affirm their adherence to established protocols for managing the outbreak.
The economic implications for both nations’ livestock industries are substantial due to the suspension of trade. The U.S. last closed its border to Mexican livestock imports in May, with plans to gradually reopen ports, but the latest northward spread has led to this immediate reclosure. Officials are keen to prevent a repeat of past outbreaks that caused significant economic losses to the U.S. cattle industry. Efforts also include exploring the use of existing anti-parasite treatments for livestock.
While primarily affecting animals, some reports from earlier this year have indicated human infections in Mexico, underscoring the broader public health dimension of this developing situation. The focus remains on containing this pest to safeguard agricultural interests and public well-being across the region.