USDA Races to Impose Quarantine After Texas Screwworm Case

Cattle graze in a field on June 2 in Quemado, Texas. (Brandon Bell/Getty Images)

The U.S. Department of Agriculture is racing to contain the deadly New World screwworm after a case was detected in Texas, where a broader outbreak could threaten an already-small domestic cattle herd.

The flesh-eating parasite was confirmed June 3 in a 3-week-old calf in South Texas, marking the first detection in the U.S. in nearly a decade. The screwworm’s presence in the country marks the latest obstacle to the Trump administration’s efforts to tackle record-high beef prices.

The key to preventing a bigger outbreak will depend on fencing in the screwworm fly, which has been gradually spreading north through Mexico over the past year. The agency is implementing quarantines, movement controls and surveillance in a 12-mile zone around the detection site in Zavala County.

“This fly typically moves great distances because humans move animals, not because the fly flies to new areas,” Agriculture Secretary Brooke Rollins said on a late June 3 call with reporters. “This is a really important point. The only way this spreads is through animal movement. It’s not because the fly flies tens of miles or hundreds of miles on its own.”

She said in a hearing before the House agriculture committee June 4 that the USDA doesn’t believe the situation will become an infestation. “We will be able to isolate each case,” Rollins said.

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Zavala County is close to the U.S.’s southern border and not part of the main cattle-producing areas of Texas, yet it still has a prominent livestock industry with an estimated 37,000 cattle. Texas, the U.S.’s largest cattle producer, had 12.1 million cattle as of January — about 14% of the U.S. herd.

The screwworm disease, while treatable in animals and posing no threat to food safety, still poses a “logistical problem” that could reduce cattle supplies if more movement restrictions and quarantines are put in place, said Ben DiConstanzo, a senior analyst at Walsh Trading. The fly is “like a roach,” he said. “If there’s one, there’s a heck of a lot more.”

The parasitic fly lays its eggs in the wounds of warm-blooded animals. After hatching, the larvae burrow into living tissue causing severe damage and, if untreated, potentially death.

We are treating the confirmed case of New World Screwworm in a Texas cattle ranch with the utmost seriousness and are responding aggressively alongside our state partners @TAHC.

USDA's proactive actions bought us nearly a year to prepare, as models had projected New World… pic.twitter.com/Ws5ceLc9ew — Secretary Brooke Rollins (@SecRollins) June 4, 2026

The U.S. has already blocked live cattle shipments from Mexico for much of the past year due to the New World screwworm’s presence, adding to supply tightness for U.S. beef processors and consumers at a time when the domestic herd is already at a 75-year low.

Those companies, including Tyson Foods and JBS NV, have faced losses in their beef businesses and resorted to closing plants amid high cattle prices that they’ve struggled to pass fully through to consumers. Shares in Tyson, the U.S.’s largest meatpacker, were little changed June 4, while JBS’ U.S. shares gained.

Tyson ranks No. 9 on the Transport Topics Top 100 list of the largest private carriers in North America and No. 1 among agriculture/food processing carriers. JBS ranks No. 86 on the TT Private 100 and No. 12 on the agriculture/food list. 

The Meat Institute, the industry group representing meatpackers, said in a statement that it “will look to USDA to brief industry stakeholders and call on them to consider allowing low-risk terminal movements for slaughter to ensure animals continue to be processed.” That includes animals headed straight to slaughter that don’t come from infested zones or are raised indoors.

The last outbreak in 1976 affected nearly 1.5 million cattle in Texas, impacting the state’s economy by as much as $375 million, according to the USDA. That would equate to about a $1.8 billion hit today, though the comparison is made difficult as the state’s cattle population has grown while its sheep and goat population is smaller, the agency said.

That outbreak was resolved by sterilizing flies with radiation and distributing them broadly to limit the screwworm’s reproduction. The USDA in Texas has completed a facility to disperse sterile flies and is building the only U.S.-based plant for the production of those flies. It is expected to produce 100 million sterile flies per week by November 2027, adding to existing production from plants in Mexico and Panama.

The U.S. Food and Drug Administration had already issued emergency authorization for several screwworm treatments, including those made by Elanco Animal Health and Zoetis Inc. The U.S. is flying some of its so-called national veterinary stockpile to Texas, Rollins said on the June 3 call. 

With the screwworm case now in the U.S., ranchers in Texas are gearing up to take on a threat they’ve been told is on the horizon for months.

Donnell Brown, a fifth-generation cattle rancher, has stocked up on aerosol spray to treat screwworm infestations, and is considering shifting his calving season to colder months when the screwworm will have a harder time spreading. 

He said if the pest reaches his Throckmorton ranch, which sells about 800 bulls a year and operates 5,000 acres, he will give calves DuraMectin, a deworming medicine, to protect them through the vulnerable newborn stage.

Declining ranch workforces add to the challenge for small cow-calf operations, which will need to increase hands-on surveillance of herds to monitor for infestations.

“We don’t have the labor force that we once had,” said Stephen Diebel, co-owner of Diebel Cattle Co. in Victoria, Texas. Diebel, who is also president of the Texas & Southwestern Cattle Raisers Association, said he has been working on educating ranchers to prevent and respond to screwworm, which he says will be necessary until the USDA’s sterile fly production reaches 500 million to 700 million flies per week.