First Case of New World Screwworm Confirmed in South Texas Cattle

Agriculture Secretary Brooke Rollins confirmed Wednesday evening that a case of New World screwworm has been detected on a cattle ranch in south Texas — the first domestic detection of the flesh-eating parasite in more than six decades.

Rollins told reporters during a news briefing that the case is the only one actively being monitored and the only one confirmed.

Rep. Chip Roy (R-Texas) posted on X that his office is monitoring a case in La Pryor, Texas – about 100 miles west of San Antonio – and working with officials to “determine next steps as we push this threat back out of the country.”

The U.S. Department of Agriculture has established a 20-kilometer infested zone, implemented quarantine and movement controls, and launched new surveillance systems in and around the zone, Rollins said.

“The only way this spreads is through animal movement,” she said.

“This pest does not cause any sort of a food-safety issue. It is not a disease, rather an insect that feeds on living tissue,” Rollins said, noting that animals treated early enough are able to recover and safely enter the food supply system.

The confirmation of the pest is bad news for the cattle and livestock industry.

After the USDA announced the possibility of a case in a post on social media earlier this week, feeder cattle futures fell as news of the possible detection spread. The potential case comes as the U.S. cattle population is already at its lowest level in 75 years.

Texas Agriculture Commissioner Sid Miller said he believes the USDA is not acting aggressively enough, and he called for the use of pesticides.

“For months, the screwworm has advanced rapidly through Mexico in spite of the USDA’s existing gameplan,” Miller said in a statement. “Even though billions of sterile flies have been dispersed by USDA, the screwworm has still advanced over 1100 miles from southern Mexico to Texas, and USDA has missed an important component. Now that it appears the first screwworm has arrived in Texas, the consequences of that decision are now staring us in the face.”

The New World screwworm — a parasitic fly whose larvae burrow into the open wounds of living animals — was eradicated from the United States in the 1960s. Its absence saves the U.S. economy nearly $3 billion annually.

A screwworm outbreak could cost Texas alone around $1.8 billion annually, with cattle producers facing up to $745 million in losses each year, according to the Texas and Southwestern Cattle Raisers Association.

The parasite has been moving north through Central America and Mexico for more than a year, with recent detections approaching the U.S.-Mexico border. As recently as Tuesday, the USDA confirmed a case in Coahuila, Mexico, roughly 25 miles south of the Texas border.

Screwworm detections in Panama surged from roughly 25 cases per year to more than 6,500 in 2023, and the parasite spread northward through Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador, and ultimately into Mexico by November 2024.

The pest’s resurgence has prompted years of escalating U.S. response efforts.

The core of the containment strategy has been the sterile insect technique — releasing infertile flies to suppress wild populations. A sterile fly dispersal facility in Edinburg, Texas, capable of releasing up to 100 million sterile flies per week, opened in February.

Rollins cast some blame on the Biden administration for the pest crossing into America, pointing to open borders as a source of the flies movement.

“This was always the problem with the last administration, open border policies, the movement of humans and their livestock from South America through Central America and through Mexico, and then, of course, the illicit movement of cattle with the cartels,” she said Wednesday.