New World screwworm, once eradicated, is reappearing in the U.S.; officials revive surveillance and control efforts

The New World screwworm, a parasitic fly whose larvae feed on living flesh, has been detected again in the United States after decades of eradication. Since June, roughly 50 cases have been reported inside the U.S., mostly in Texas. Mexican authorities continue to report a much larger outbreak, with nearly 2,000 active cases across parts of Mexico.

The screwworm infests wounds on livestock, wildlife and pets and can affect people in rare instances. Before eradication campaigns in the mid-20th century, the pest caused serious livestock losses in the southwestern U.S. The recent detections restore the risk of direct animal harm and financial strain for producers in border states.

Federal agents recently caught the first wild screwworm fly in Brewster County, Texas, in one of the USDA's more than 100 screwworm-specific traps along the U.S.-Mexico border. That capture shows wild flies are circulating beyond the handful of confirmed infected animals. At the time of reporting, active confirmed animal cases included a horse in Presidio County, Texas, and a horse in Grant County, New Mexico.

Surveillance: The USDA has deployed a network of dedicated screwworm traps along the border. Agencies are monitoring livestock, domestic animals and wild animals for signs of infestation.

Control strategy: Officials are reviving eradication techniques used in earlier successful campaigns. Past U.S. eradication programs relied on coordinated tactics that suppressed wild populations and interrupted transmission.

Research and prediction tools: Researchers at the University of California San Diego have developed a tracking system intended to predict where the pest could strike next. The tool aims to guide surveillance and response placement.

Capacity building: Private efforts and public-private initiatives are emerging to expand U.S. capacity to respond. One planned biosecurity platform in San Antonio aims to build response infrastructure with screwworm as an initial target.

What this means for livestock and border policy

States near the border will likely keep heightened surveillance and movement controls to limit spread. Reopening ports for cattle imports or other cross-border trade will be evaluated in the context of current detections. The presence of wild flies complicates containment because wild vectors can move beyond monitored herds.

Practical steps for livestock owners

• Inspect animals regularly, especially for wounds or signs of infestation. Early detection improves treatment outcomes.

• Report suspicious lesions or unusual fly activity to agricultural authorities promptly.

• New detections of wild flies or cases in wildlife, which would indicate broader environmental spread.
• Changes in the number and geographic distribution of reported U.S. cases beyond the current clusters.
• Progress in deployment of predictive tracking systems and the San Antonio biosecurity platform.
• Policy decisions on cross-border livestock movement tied to active outbreak status in Mexico.

The screwworm outbreak in Mexico has spilled northward, producing multiple U.S. cases and the first confirmed wild fly capture. Federal, state and research organizations are stepping up surveillance and reviving control methods used in previous eradication efforts. Livestock owners in affected regions should increase inspections and follow official reporting channels.