Screwworm in Sonora: Will First Case Halt Scheduled Aug. 24 Border Reopening?

Just days before the U.S.-Mexico port in Douglas, Ariz., is scheduled to reopen to livestock on Monday, Aug. 24, 2026, the Mexican state of Sonora has confirmed its first case of New World screwworm (NWS).

According to Reuters, “Mexico’s Sonora state has activated emergency surveillance, ‌containment and control protocols following the detection of its first case of screwworm, Governor Alfonso Durazo said on Wednesday [Aug. 19, 2026].”

Sonora is just south of Arizona. According to KJZZ, a Phoenix radio station, the case was reported in a cow in the southern region of Sonora, about 10 miles from the border with the Mexican state of Chihuahua and 292 miles from the U.S. border. Sonora’s Ministry of Agriculture (SAGARHPA) reports 360,000 sterile NWS flies have been released in the area around the state’s first case.

The Sonora detection was just days after a case was reported in Ciudad Juárez, Mexico. The canine is located 18 miles from the U.S. border. Juarez is located in the state of Chihuahua, which is currently reporting 75 active NWS cases. Juárez is the border city to El Paso, Texas.

Since the first NWS was found in the U.S. on June 3, USDA has reported 46 confirmed cases. Currently there are two active cases.

What Does This Mean for the Aug. 24 Reopening?

On Thursday afternoon, USDA responded to the Sonora confirmation on X saying: “We have no plans to change the Douglas, Ariz., port reopening on 8/24.”

The USDA’s Animal and Plant Health Inspection Service (APHIS) previously announced a phased reopening of southern ports to livestock trade, beginning with the Agua Prieta-Douglas crossing on Monday, Aug. 24, 2026. Historically, Sonora and Chihuahua have been categorized as low-risk zones. However, the USDA has explicitly stated that the reopening schedule is flexible and will be paused if U.S. authorities identify an increased risk in either state.

The post also says: “For 18 months we have built a coordinated, highly sophisticated system inlcuding the monitoring of more than 100 NWS traps, 8,000 insect traps, high-tech drone detection, 100 million sterile flies dispersed per week in Mexico and Texas, and an investment in an additional 100 million sterile flies in Metapa Mexico. The Metapa facility, which is already producing sterile flies, will soon start producing the NovoFly which will double the effectiveness of the sterile insect technique. We will have more resources layering on soon.

“Last month we added the most complete entry inspection protocols possible. This includes enhanced surveillance, rapid diagnostic capacity, pre-treatment processes weeks in advance, layered inspections before and at the port, sophisticated communication and coordinated response protocols designed to protect American agriculture.”

USDA reports the necessary resources — personnel, technology, laboratory support and interagency coordination — are in place and ready in Douglas.

“We remain committed to continuous monitoring and will adjust protocols as conditions warrant to maintain the highest standards,” the X post says. “These measures provide the assurance required to resume livestock trade while safeguarding animal health.”