First screwworm case detected in Mexican state of Sonora

Key facts

• Sonora, Mexico, has confirmed its first case of the New World screwworm parasite in a cow.
• The detection occurred in the southern region of Sonora, approximately 10 miles from the border with Chihuahua.
• Mexico's Governor Alfonso Durazo announced emergency surveillance and containment measures.
• The U.S. Department of Agriculture plans to reopen the border to Mexican cattle imports on August 24, 2026.
• 360,000 sterile New World screwworm flies have been released in the affected area.

Sonora, Mexico, has confirmed its first case of the New World screwworm parasite in a cow, prompting the state to activate emergency surveillance and containment protocols. Governor Alfonso Durazo announced on social media that sanitary cordons and control actions have been reinforced to prevent the spread of the flesh-eating parasite.

The detection comes just days before the U.S. Department of Agriculture (USDA) is scheduled to reopen the border to Mexican cattle imports on August 24, 2026, starting with the Agua Prieta-Douglas crossing from Sonora into Arizona. The U.S. had barred cattle from Mexico for over a year to prevent the spread of screwworm.

Juan González Alvarado, Sonora’s state agriculture minister, stated that an international force has been mobilized to contain and eradicate the parasite. Mexico has released 360,000 sterile New World screwworm flies in the area around the confirmed case, a method considered effective by the USDA for eradication.

The USDA has identified Sonora and Chihuahua as the lowest-risk Mexican states due to their inspection programs and geographic distance from southern Mexico, where most cases are concentrated. The reopening timeline for ports may be adjusted based on Mexico's progress in addressing the issue and any identified increase in risk.