A confirmed New World screwworm case in the Mexican state of Sonora is raising questions just days before the United States is scheduled to begin reopening a border crossing to Mexican cattle.
Reuters reported Sonora confirmed its first case and activated emergency surveillance and containment measures. USDA previously announced the Douglas, Arizona, port would begin accepting livestock Aug. 24, 2026, as part of a phased reopening, provided Mexico continued meeting requirements under a joint action plan.
USDA’s Animal and Plant Health Inspection Service says screwworm larvae infest wounds in warm-blooded animals and can cause severe injury or death if untreated. The United States has restricted Mexican cattle movements while officials work to prevent the parasite from moving north.
Drovers reported the Sonora discovery could complicate the reopening timeline. U.S. cattle producers are watching closely because imported feeder cattle affect supplies, while introduction of screwworm could create major economic losses for ranchers and livestock markets.
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