Federal and state officials confirmed Wednesday that New World screwworm has been detected in a calf in Zavala County, marking the first case in Texas livestock since the parasite was eradicated from the United States in 1966.
The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service announced the confirmation after larvae from a three-week-old calf in La Pryor tested positive at the national veterinary lab in Ames, Iowa. The larvae were found in the animal’s umbilical area. No additional cases have been confirmed so far.
Texas Animal Health Commission officials immediately established a quarantine zone and are working with USDA partners on surveillance, movement controls, and sterile fly releases to contain the outbreak. The infested zone covers parts of Zavala and Uvalde counties.
Just wrapped up a virtual meeting with ~50 of our outstanding Texas cattle ranchers and @TAHC. I also have been in contact with @GregAbbott_TX, @LtGovTX, and the @Burrows4TX team.
— Secretary Brooke Rollins (@SecRollins) June 3, 2026
Our food supply is 100% safe. This potential New World Screworm detection is being fully contained… https://t.co/dRd6KjmB2J
New World screwworm flies lay eggs in open wounds of warm-blooded animals. The hatching larvae feed on living tissue, causing severe damage that can lead to death if untreated. The pest was a major threat to Texas’ cattle industry before a successful eradication program using sterile flies ended its presence in the U.S. six decades ago.
The detection comes after more than a year of rising concern as the fly moved northward through Mexico. Texas agriculture officials had already expanded sterile fly dispersal operations and opened a new facility near Edinburg to help block further spread.
The case poses a potential risk to the state’s multibillion-dollar cattle industry, wildlife, and pets. Officials stress that beef from properly inspected animals remains safe for consumers.
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