USDA Confirms New World Screwworm Case in South Texas
The U.S. Department of Agriculture confirmed Wednesday that a case of New World screwworm has been detected in South Texas, marking the first confirmed U.S. case tied to the parasite’s recent northward spread through Central America and Mexico.
According to Agriculture Secretary Brooke Rollins, testing at the National Veterinary Services Laboratories in Ames, Iowa, confirmed the infection in a three-week-old calf in Zavala County, Texas. The USDA said it is working with the Texas Animal Health Commission to establish an incident command team and deploy response personnel to the area.
Officials plan to create a 20-kilometer, or 12.4-mile, zone around the confirmed case. The zone will include quarantine measures, livestock movement restrictions, increased surveillance, and additional fly trapping.
New World screwworms are parasitic flies whose larvae feed on the living tissue of warm-blooded animals. Livestock are considered especially vulnerable, though other animals and humans can also be affected. The parasite was once present in the United States but was eradicated in the 1960s through the widespread release of sterile male flies, a method known as the Sterile Insect Technique.
For decades, a control barrier in Panama helped prevent the pest from moving north. That barrier was breached in 2022, and cases have since been reported through Central America and Mexico. Recent detections in Coahuila, Mexico, had placed the parasite within several dozen miles of the U.S. border.
Before Wednesday’s confirmation, reports of possible cases near Texas prompted concern in the cattle industry and public disagreement over whether detections had been verified. USDA officials had urged caution regarding unconfirmed claims.
In response to the confirmed Texas case, the USDA said it will increase sterile fly releases in the area, including ground-based releases in addition to aerial dispersal. The agency is also supporting construction of a $750 million sterile fly production facility in South Texas.