New World Screwworm Detected in South Texas Calf

The New World screwworm fly, a parasite that targets livestock, wildlife, and pets, has been discovered in a young calf in La Pryor, Texas. This represents the first case in U.S. cattle since the 1960s, according to the Agriculture Department.

Brooke Rollins, the agriculture secretary, announced quick measures to contain and eliminate this threat in South Texas during a news briefing. The screwworm can severely harm the American cattle industry if it spreads beyond this single case.

Though the screwworm had been absent from North and Central America since the mid-2000s, its presence was detected on Mexico’s border with Guatemala in November 2024. The screwworm flies have a limited flight range but can spread through infected animals moving to new locations. Over 20,000 cases have been reported in Mexico, leading to a ban on Mexican cattle entering the United States for more than a year.

The screwworm does not affect fruits or vegetables. The Agriculture Department assures that all beef, poultry, and eggs are safe for consumption through their Food Safety and Inspection Service.

To combat the threat, a 20-kilometer quarantine zone has been established around the location of the infected calf, with increased monitoring and restrictions on animal movement. The Texas Animal Health Commission, along with department veterinarians, is actively working in the area.

The strategy includes releasing millions of sterile screwworm flies, both by air and truck, to lower the population. Only one facility in Panama currently produces about 100 million sterile flies weekly. Additionally, the U.S. Army Corps of Engineers is developing a $750 million facility at Moore Air Base in Edinburg, Texas. By late 2027, this facility is projected to produce 100 million sterile flies weekly, with plans to eventually increase capacity to 300 million flies per week.