The U.S. Department of Agriculture has confirmed the first case of New World screwworm in the United States since 1966, triggering an aggressive federal and state response in South Texas as officials work to contain and eradicate the flesh-eating parasite before it can spread.
Agriculture Secretary Brooke Rollins announced the confirmation Wednesday evening during a briefing with Texas media, saying laboratory testing at USDA’s National Veterinary Services Laboratories in Ames, Iowa, confirmed New World screwworm in a 3-week-old calf in La Pryor, Texas, located in Zavala County roughly 50 miles from the Mexican border.
“We have confirmed the first official case of New World Screwworm in Texas,” Rollins said.
The infected animal was discovered on a cow-calf operation after a private veterinarian collected samples and submitted them through the Texas Animal Health Commission for testing.
Federal and state officials emphasized that only one confirmed case has been identified and that no additional detections have been reported.
In response, USDA and the Texas Animal Health Commission have established a unified incident command structure and deployed animal health personnel to the area. Officials have also created a 20-kilometer infested zone surrounding the detection site and implemented quarantines, movement controls and enhanced surveillance measures.
Texas Animal Health Commission Executive Director Dr. Buddy Dinges said all warm-blooded animals within the quarantine zone are subject to movement restrictions.
“Please help us prevent any further movement of this pest by staying put and contacting the Texas Animal Health Commission if you need to be permitted out,” Dinges said. “No movement of warm-blooded species will be allowed out of this zone without an inspection by an animal health official.”
USDA has dispatched a five-member strike team consisting of veterinary medical officers and animal health technicians to assist Texas officials with inspections, surveillance, outreach and containment efforts. Additional personnel are standing by if needed.
The agency has also accelerated the release of sterile flies, the cornerstone of the eradication strategy that successfully eliminated New World screwworm from the United States six decades ago.
Rollins said USDA immediately deployed four million sterile flies through ground release chambers around the affected area. Those releases are in addition to approximately four million sterile flies already being dispersed aerially each week in the region.
Officials revealed that USDA had already begun proactively releasing sterile flies into South Texas months before the first U.S. detection occurred. Since February, more than 129 million sterile flies have been dispersed through aerial, vehicle and ground-based release systems.
“We were starting to lean forward aggressively just in case something like this happened,” said Rear Adm. Patrick Schmoyer of USDA’s Animal and Plant Health Inspection Service.
The agency has also increased trapping and surveillance efforts near the border and expanded monitoring programs involving livestock, wildlife and companion animals.
According to Rollins, USDA has deployed more than 8,000 traps along the U.S.-Mexico border over the past year and examined more than 58,000 fly samples and 19,000 wildlife animals without a single confirmed detection until this week.
“This is not something we’ve been sitting back and waiting for,” Rollins said.
Officials repeatedly stressed that the discovery does not represent a food safety threat.
New World screwworm is not a disease but rather the larval stage of a parasitic fly that feeds on living tissue. Female flies lay eggs in open wounds or body openings of warm-blooded animals. Once the eggs hatch, the larvae burrow into healthy flesh, creating painful and potentially devastating infestations.
The pest can affect cattle, sheep, goats, horses, wildlife, pets and, in rare cases, humans.
“This is not a food safety issue. This is a food production issue,” Dinges said.
Rollins emphasized that screwworms do not infest meat, fruits, vegetables or processed food products. USDA’s Food Safety and Inspection Service also maintains inspection procedures designed to prevent any affected animals from entering the food supply.
Officials said the infected calf is expected to recover because the infestation was identified and treated early.
“Once removed and cleaned, animals treated early enough will recover and are safe to enter the supply system,” Rollins said.
Federal and state officials are also urging pet owners to remain vigilant. Rollins noted that dogs and cats have accounted for some screwworm detections in northern Mexico and encouraged residents to inspect pets for wounds, unusual drainage or signs of discomfort.
USDA has deployed trained detector dogs to border crossings and plans to increase inspections involving animals entering the United States.
Authorities are asking producers and animal owners to report suspicious wounds immediately and monitor livestock closely.
“Quick notification leads to quick detection and quick response to stop the pest from spreading,” Dinges said.
Congressional agriculture leaders sought to reassure producers following the announcement.
House Agriculture Committee Chairman Glenn “GT” Thompson, R-Pa., and Senate Agriculture Committee Chairman John Boozman, R-Ark., praised USDA’s preparations and emphasized that officials have spent more than a year planning for the possibility of a domestic detection.
“For well over a year, Secretary Brooke Rollins and her team at USDA have been working around the clock alongside federal agencies, state partners and animal health experts to prevent New World Screwworm from entering the United States—longer than many thought possible—and to ensure we are prepared to respond to a potential domestic case,” the lawmakers said in a joint statement.
“The detection of New World Screwworm within our borders should not be cause for panic, but rather time for the full deployment of the next phase of the whole-of-government response USDA has been planning for months.”
The confirmation follows months of concern over the parasite’s steady advance through Central America and Mexico.
USDA officials said the current outbreak began after New World screwworm breached a long-standing biological barrier in Panama’s Darien Gap in 2021. Cases increased significantly in Panama by 2023 before spreading northward through Central America and eventually into southern Mexico in late 2024.
Rollins said federal models suggested the pest could have reached Texas as early as summer or fall 2025.
“I do want to give a shout out to the team at APHIS, our Texas Animal Health Commission, Dr. Dinges and his team, all of our friends in Texas,” Rollins said. “We have been able to successfully keep it out of Texas a year longer almost than what was thought, which has allowed us to prepare for today.”
The United States has a long history battling New World screwworm. The pest was first documented as a major livestock problem in the Southeast during the 1930s, prompting decades of research and eradication efforts.
The breakthrough came in the 1950s when scientists discovered that sterilized male flies could be released into the wild to collapse screwworm populations. Female flies mate only once, making the sterile insect technique exceptionally effective.
The strategy successfully eliminated New World screwworm from the Southeast by 1959 and from the continental United States by 1966. Additional eradication campaigns pushed the parasite out of Mexico in 1986 and eventually through Central America by 2006.
A small outbreak in Florida’s Key Deer population was successfully eradicated in 2017 using the same approach.
Today, USDA’s primary sterile fly production facility in Panama produces more than 100 million flies per week. The agency has invested an additional $21 million to renovate a production facility in Metapa, Mexico, which is expected to begin operations this month and eventually produce up to 100 million additional flies per week.
USDA is also investing $750 million in a sterile fly production facility at Moore Air Base in South Texas. Once operational, the facility is expected to produce approximately 300 million sterile flies per week and become the largest facility of its kind in history.
Officials estimate that between 400 million and 500 million sterile flies per week may ultimately be needed to fully eradicate the current outbreak and push the parasite back toward its historical containment zone.
For now, animal health officials say their focus remains on containment.
“We have the tools, resources and an action plan to aggressively respond, enhance surveillance and prevent further spread,” Thompson and Boozman said.
As inspectors, veterinarians, ranchers and animal health officials mobilize across South Texas, USDA leaders say the next several weeks will be critical in determining whether the detection remains an isolated case or becomes the start of a broader outbreak.
“We have successfully eradicated this threat to livestock, wildlife and animal health before,” Thompson and Boozman said. “And we’re confident we will do so again.”
