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Screwworm Spreads Beyond Initial Control Zone
Number of Infections Grows to a Dozen, Adding Urgency to Containment Efforts
Key Takeaways:
- New World screwworm infections in Texas have expanded beyond an initial zone to at least a dozen cases, including cattle and sheep, prompting heightened containment efforts.
- The parasite threatens a U.S. cattle herd already at a 75-year low, with movement restrictions likely to slow rebuilding and potentially drive beef prices higher.
- Officials are relying on sterile fly releases to contain the outbreak, but expanded U.S. production will not ramp up until November 2027, leaving near-term uncertainty over spread.
The New World screwworm is stretching beyond an initial control zone in Texas as the number of infections grows to a dozen, adding some urgency to efforts to contain the deadly pest threatening the U.S. cattle herd.
The parasitic fly was detected in a sheep in Sutton County and a head of cattle in Tom Green County late last week, about 200 miles away from the first U.S. case in South Texas, according to the U.S. Department of Agriculture. That brings the total number of infections to at least a dozen, including eight heads of cattle.
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Further spread in Texas or in other states “would be a very bad milestone,” said Andy Moorhead, an associate professor at North Carolina State University. Moorhead, who also leads the American Association of Veterinary Parasitologists, said the conversation at the group’s annual meeting earlier this month was “nothing but screwworm.”
The screwworm is a fly that lays its eggs in the open wounds of warm-blooded animals. Its larvae burrow into flesh and can kill animals if left untreated. The initial case in Zavala County was the first in the U.S. in a decade and the first in domestic livestock in about five decades.
While screwworm doesn’t affect food safety, it poses a risk to the U.S. cattle industry, as drought and high production costs have culled the nation’s herd to a 75-year low. Restrictions on movement are likely to delay the rebuilding of the herd, which may send record beef prices even higher for consumers.
Gov. Abbott launched a free online course to certify additional New World Screwworm inspectors across Texas.
This initiative empowers people, & private industry, to inspect & certify livestock movement, ensuring the safety of our cattle, wildlife, & food supply remains secure. pic.twitter.com/2Oj9GkrkpR — Governor Abbott Press Office (@GovAbbottPress) June 13, 2026
Under the restrictions, animals cannot be moved outside of the affected areas without authorization, and Texas Animal Health Commission representatives also need to inspect carcasses prior to removal from the zones.
The short-term movement protocols are already giving the state’s ranchers “many more advantages” than in the 1970s when the pest spread among 1.5 million head of cattle in Texas, said Stephen Diebel, the president of the Texas and Southwestern Cattle Raisers Association.
Still, the strategy that worked best to eradicate the screwworm back then — and the government’s main weapon in the current outbreak — is more than a year away from being fully implemented. The battle plan involves churning out an army of sterile flies to halt reproduction of the parasite, and the plant in Texas that’s targeted to significantly ramp up output of the flies isn’t slated to begin operating until November 2027.
Currently, the only sterile fly facility is a plant in Panama that’s producing only a fraction of the insects needed to mount an effective response. The concern is over how far screwworm will spread before the U.S.’s plan is fully operational.
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Agriculture Secretary Brooke Rollins said last week that the U.S. is “not going to be able to eradicate it until we’ve got the couple hundred million more flies coming in, but we will be able to contain it.” She added that she doesn’t “have a good enough sense yet” of how far screwworm might spread in the meantime.
Diebel also couldn’t speculate on the possible spread of the parasite, but said “there’s very good measures in place with our existing fly production dispersals” that will keep producers in good shape until the output increases.
Others see more urgency in getting the Texas plant up and running. The U.S. will probably be “handicapped for a while” in its sterile fly dispersal, and even then the spread will depend on how effectively those flies mate, said Arlan Suderman, the chief commodities economist at StoneX Group.
“My fear is that we’re talking about two to three years” to curb the spread, Suderman said. “But part of that depends on how many New World screwworms are already in the United States. The likelihood that there’s more is certainly there.”
