Reemergence of New World Screwworm in Texas

The New World screwworm fly has appeared in South Texas, marking the first case in the U.S. since the 1960s. This development was confirmed by the Agriculture Department after a 3-week-old calf in La Pryor, Texas, was found infected.

The screwworm is a fly whose larvae consume the tissue of livestock, wildlife, and pets. This case represents the first detection in U.S. cattle since the species was eradicated in the 1960s. Secretary of Agriculture Brooke Rollins announced the department’s quick actions taken to contain and eradicate the screwworm in the region.

The risk is significant. If additional cases are discovered, untreated infections could severely impact the American cattle industry. The Agriculture Department had been on alert for the screwworm’s return since the parasite was detected at the Guatemalan-Mexican border in 2024.

Screwworm flies are not highly mobile. However, they can spread when infected animals are transported. More than 20,000 cases have been found in Mexico. As a precaution, Mexican cattle have been restricted from entering the U.S. for over a year.

The screwworm does not affect produce, and the Agriculture Department ensures all beef, poultry, and eggs are safe for consumption. The department has established a 20-kilometer quarantine zone in La Pryor to monitor and control animal movement.

Additionally, millions of sterile New World screwworm flies are being released in the area. This method involves releasing sterile males to mate with wild females, reducing the fly population. Currently, a facility in Panama produces 100 million sterile flies weekly. A new U.S. facility is under construction in Edinburg, Texas, expected to produce 100 million to 300 million flies weekly by late 2027.