As US border reopens to Mexican cattle, concerns persist over screwworm spread

• Chihuahua state has reported 67 confirmed screwworm cases since first detection in July, while neighboring Sonora reported 2 cases after its first detection last week
• Mexico recently opened a sterile-fly production facility in Chiapas, while the US is building its own plant in Texas expected to be completed by spring 2027
• The phased reopening remains contingent on Mexico's compliance with screwworm-control measures, despite concerns from US cattle groups that resuming imports could increase parasite risks

Summary

The U.S. resumed imports of Mexican cattle on August 24 under a phased reopening, over a year after imposing a ban to prevent the spread of New World screwworm, a flesh-eating parasite. Imports will initially flow through Arizona before expanding to additional ports in New Mexico.

Key Developments:

Mexico is intensifying screwworm containment efforts in northern border states. Chihuahua, a major cattle-exporting state, has confirmed 67 screwworm cases since first detection in July. Neighboring Sonora reported two cases after its first detection last week. Both states have activated emergency surveillance protocols, including increased inspections and livestock movement controls.

Containment Strategy:

Mexican Agriculture Minister Columba Lopez announced reinforced deployment of sterile flies in Sonora and Chihuahua. This sterile insect technique involves releasing sterilized screwworm flies that mate with wild females but produce no offspring, gradually reducing the pest population. Mexico recently opened a sterile-fly production facility in Chiapas, while the U.S. is constructing its own plant in Texas, expected to be operational by spring 2027.

Market Concerns:

The phased reopening has drawn criticism from U.S. cattle groups and state officials who argue that resuming imports poses screwworm risks, particularly as the parasite has already been detected in Texas and New Mexico. The USDA stated the reopening remains contingent on Mexico's compliance with screwworm-control measures.

Implications:

The controlled resumption of cross-border cattle trade is critical for both countries' livestock industries, but concerns persist about adequate containment of the parasite's northward spread.