A three‑week‑old calf in La Pryor, Texas, has been confirmed with a New World screwworm infestation, marking the first U.S. case since 1966.. The parasite, Cochliomyia hominivorax, was found about 100 miles southwest of San Antonio and 50 miles from the Mexican border, prompting immediate quarantine measures. Authorities warn that the outbreak could jeopardize Texas’ $17 billion cattle industry and the broader $113 billion U.S. livestock sector.

First U.S . Screwworm Case Since 1966 Detected in La Pryor Calf

Veterinarians in Zavala County identified the larvae on a newborn calf on a ranch near La Pryor, confirming the parasite’s presence on U.S. soil for the first time in six decades. The USDA announced the finding on Tuesday, noting that the calf’s open navel wound likely attracted the female flies that lay eggs on living tissue. "Even the navel of newborn calves can serve as an entry point," said Lee Haines, a research associate professor at the University of Notre Dame, highlighting how routine livestock practices create vulnerabilities.

Texas' $17 Billion Cattle Industry Faces Immediate Quarantine

State officials have erected a 12‑mile quarantine zone around the outbreak site, restricting animal movement without USDA inspection. Texas & Southwestern Cattle Raisers Association president Stephen Diebel warned that “small injuries are enough” for the flies to infest livestock, underscoring the rapid risk to herds across the region. The quarantine aims to contain the parasite while farmers are urged to inspect animals daily and report any wounds.

Sterile Insect Technique May Return After 60‑Year Hiatus

The federal government is weighing a revival of the sterile insect technique that eradicated screwworms in the 1960s. That program released millions of sterilized male flies to out‑compete wild females, eventually collapsing the population.. USDA Secretary Brooke Rollins indicated that “resuming sterile fly releases will require coordination and substantial funding,” signaling a possible return to the historic method if the outbreak spreads.

Climate Change Linked to Screwworm’s Northward Surge

Scientists attribute the parasite’s re‑emergence to milder winters that no longer kill off northern fringe populations. Haines explained that “cold snaps that once killed off winter populations are diminishing as temperatures rise,” allowing the flies to survive farther north than before.. While Rollins blamed Mexico’s animal‑movement controls for the incursion, experts point to a warming climate as the primary driver of the species’ northward expansion.

Will Mexico’s Border Controls Prevent Further Spread?

Despite the USDA’s closure of live cattle imports from Mexico since July 2025, thousands of cases persist across the border. Critics note that the current measures may be insufficient, as the parasite can hitch rides on wildlife or illegally moved livestock. The question remains whether stricter biocontainment protocols in Mexico will curb additional incursions into the United States.