After almost 60 years without a confirmed domestic case, USDA confirmed the first U.S. detection of New World Screwworm (NWS) in South Texas on June 3. Since that time, additional detections have been confirmed in Zavala, LaSalle and Gillespie Counties in Texas, as well as Lea County, New Mexico.
After more than two decades of containment, NWS reemerged in Panama and Costa Rica in 2022. As it became widespread, Panama declared a state of emergency in 2023 before being detected in Chiapas, Mexico, in November 2024. Since then, the pest has continued moving northward through Mexico, resulting in more than 27,000 reported detections.
NWS is a parasitic pest that infests the living tissue of warm-blooded animals, including livestock, pets, wildlife and, less commonly, birds and people.
NWS was first documented as a significant problem in the Southeastern United States in 1933, though it had been present long before that. In 1958, Sterile Insect Technique (SIT) was implemented to combat NWS in the Southeast and NWS was effectively eradicated in 1966. By 2000, NWS had successfully been eliminated in areas North of the Darian Gapin Southern Panama.
The timeline of the reemergence: -Panama barrier breached ( 2022); Panama state of emergency (2023); -Mexico confirms NWS detected in Chiapas, Mexico as it advances to more that 27,000 reported detections by mid-2026 - U. S. closes border to Mexican livestock (May 2025); -Nuevo Leon, 70 miles from Texas, confirms NWS near Monterrey- Laredo commercial corridor September 2026; -Preemptive sterile fly releases being in Texas (January 2026); -Coahuila confirms NWS 25 miles from Texas (early June 2026); - First US case in Zavala County in 3-week-old calf; 12-mile quarantine zone established (early June 2026); - Second US case in Zavala County in 1-month-old calf; governor expands disaster declaration; wider surveillance zone activated (early June 2026); -Third, fourth and fifth US cases in a calf, dog and goat in La Salle and Gillespie counties in Texas, and Lea County, New Mexico (early June 2026).
While the recent U. S. cases have heightened concern among animal health officials and livestock producers, it is important to note that NWS does not threaten the safety of the U.S. food supply. But is does underscore the northward movement out of Mexico.
Governor Greg Abbott on Jan. 29 issued a statewide disaster proclamation for all counties in Texas due to the threat NWS poses to the state’s livestock industry, economy, and the potential for widespread and severe property damage for Texas. The proclamation has been renewed each month since.
When NWS was detected in Zavala County, a quarantine was imposed on the infested Zone 1 and animal movement restricted. The quarantine order, pursuant to Texas Agriculture Code, Chapters 161 – 168, and applicable regulations found in Title 4 of the Texas Administrative Code, Part 2, Chapters 31 – 60, was signed by Lewis R. Dinges, D.V.M., executive director of the Texas Animal Health Commission.
The quarantine stated that warm-blooded animals were not allowed to be moved without prior authorization, and owners had to comply with all conditions, which included inspections, treatment and a permit, before transporting beyond the quarantine boundaries, The quarantine extended to hides, carcasses, and parts of any animal capable of serving as a host for NWS.
The U.S. Department of Agriculture (USDA), Texas Animal Health Commission (TAHC), Texas Parks and Wildlife Department (TPWD) and other partners are working to stop the spread of the pest. Central to that effort is the sterile insect technique, the same eradication strategy that successfully eliminated NWS from the U.S. in the 1960s.
Containment depends on rapid detection and reporting, which can be challenging due to the size and diversity of farms and ranches and presence of wildlife. Sterile fly supply is a key constraint with current production insufficient for the expanding outbreak.
The sterile fly program was underway before New World screwworm was confirmed in Texas, positioning federal and state officials to respond quickly when the first case was identified.
The USDA began ground dispersal operations from Moore Air Base in Edinburg earlier this year as NWS cases moved north through Mexico. Now, with multiple cases confirmed in Texas, those operations have become a key component of state and federal eradication efforts.
As part of current response efforts, USDA partnered with the U.S. Army Corps of Engineers to establish a domestic sterile fly production facility and dispersal center at Moore Air Base in Edinburg.
“Moore Air Base was chosen because of its close proximity to the border, which allows us to disperse the sterile flies into multiple areas where they’re needed,” said Gabe Lopez, logistics facility operations specialist at Moore Air Base. “We’re about 20 miles north of the U.S.-Mexico border, so logistically Moore Air Base allows us to do both ground dispersal and aerial dispersal in targeted areas.”
“They start falling into these augers, and then they get blown out through the pipe that comes out of the ground release truck,” Cruz said. “Right now, we’re dispersing between 36 to 38 liters of flies, which comes out to roughly 250,000 sterile flies.”
The truck travels about 10 miles per hour while dispersing the flies across targeted areas.
“For every single fertile fly, we want to see at least 10 sterile flies that we’re releasing,” Cruz said.
Texas Farm Bureau (TFB) is also working with state and federal officials on response and preparedness efforts, including supporting efforts with congress and USDA to strengthen domestic sterile fly production and dispersal capacity in the United States.
TFB President Russell Boening, upon hearing of the confirmed detection of NWS in the state said, “Federal and state agencies are actively implementing a New World screwworm response plan that was prepared and ready for this circumstance. Livestock owners and all Texans should remain vigilant. Surveillance and reporting are a priority. The quicker an infestation is found, the quicker the New World screwworm can be eradicated. The detection of New World screwworm does not impact on the safety of our food supply. NWS do not infest meat, fruits, vegetables or other food sources.”
“Expanding sterile fly dispersal and strengthening domestic response capabilities are key steps in slowing the movement of New World screwworm and protecting livestock, wildlife and animal health,” said Tracy Tomascik, TFB associate director of Commodity and Regulatory Activities.
Additional response operations are also underway in Mexico. The country is conducting aerial releases across affected regions and has implemented movement restrictions and animal inspections.