The New World screwworm, a fly whose larvae consume the tissue of livestock, wildlife, and pets, has been discovered in a 3-week-old calf in La Pryor, Texas. The Agriculture Department confirmed the case on Wednesday night, marking the first screwworm detection in U.S. cattle since its eradication in the 1960s.
Agriculture Secretary Brooke Rollins stated at a news conference, “We are taking immediate action to deploy resources, contain, and eradicate this outbreak of the New World screwworm in South Texas.” If additional screwworms are discovered beyond this initial case, the infestation could severely impact the American cattle industry.
The Agriculture Department anticipated the screwworm’s potential return to the United States for several months. By the mid-2000s, screwworms were eradicated from all of North and Central America. However, the parasite has been moving north and was identified at Mexico’s border with Guatemala in November 2024.
Screwworm flies spread primarily through the movement of unknowingly infected animals, particularly those transported to new locations. More than 20,000 cases have been documented in Mexico, leading to a ban on Mexican cattle entering the United States for over a year.
The flies do not infest fruit or vegetables. The Agriculture Department assures that its Food Safety and Inspection Service will guarantee that beef, poultry, and eggs remain safe for consumption.
A 20-kilometer “infested zone” quarantine has been declared where the infected calf was found, ramping up surveillance and restricting the movement of warm-blooded animals from the area. The department has deployed veterinarians and animal health officials, in collaboration with the Texas Animal Health Commission.
Efforts include dispersing millions of sterile New World screwworm flies from the air and by truck in the affected region. Releasing sterile flies, which mate with wild females and drive the population toward eradication, is currently the only technique available to control the fly’s spread.
Currently, a facility in Panama produces sterile flies, generating around 100 million per week. The U.S. Army Corps of Engineers has initiated construction of a $750 million production facility at Moore Air Base in Edinburg, Texas. The new facility aims to begin producing 100 million sterile flies weekly by late 2027, eventually reaching up to 300 million per week.