Texas confronts resurgence of New World screwworm affecting livestock

Texas officials warned residents of a difficult summer after a New World screwworm infestation was confirmed in a three-week-old calf on June 3. The parasite, whose larvae feed on the flesh of warm-blooded animals, has since been identified in 15 U.S. cases, primarily in cattle, with additional reports in sheep, goats and a dog. No human infections have been linked to the current outbreak.

The Centers for Disease Control and Prevention has classified the situation as a Level 3 public health emergency and is urging clinicians to report any suspected cases. The U.S. Department of Agriculture (USDA) is conducting weekly releases of 100 million sterile flies from its Panama facility and is modernizing a Mexican production site, while a new $750 million fly-rearing plant in Texas is slated to open next year. The agency is also seeking approval for a genetically engineered all-male fly strain.

State and local authorities have enacted movement restrictions, expanded surveillance, and offered free training for screwworm inspectors. Texas Governor Greg Abbott declared a disaster emergency, authorizing the use of state resources to support containment efforts. USDA Secretary Brooke Rollins emphasized that the agency now “knows what the enemy looks like” and is coordinating with private landowners, wildlife officials and researchers to deploy traps, drones and novel treatments.

Experts note that the parasite’s re-emergence traces back to a breakdown of the Panama barrier in 2023 and point to challenges such as reduced efficacy of sterile-male releases and cross-border livestock movement. Historically, a sterile-insect technique eliminated screwworm from the United States by the mid-1960s, a success the current response aims to replicate.