A new detection of New World screwworm (NWS) in northern Mexico has prompted renewed vigilance across the cattle industry. USDA officials confirmed the case in Montemorelos, Nuevo León, roughly 120 miles south of the Texas border, after identifying the parasite in a 22-month-old bovine transported from Veracruz to a local feedlot.
This marks the northernmost active case currently found in Mexico and the second detection at the same feedlot since October. Both instances appear linked to animal movement from southern Mexico rather than local spread.
Texas Agriculture Commissioner Sid Miller emphasized that while Texas remains free from NWS, the industry cannot let its guard down. “We have beaten it before with resolve and science, and we’ll do it again,” Miller said. “But Texas must stay vigilant.”
Why This Detection Matters
The New World screwworm is considered one of the most damaging livestock pests ever encountered in North America. Before eradication efforts, it caused significant animal losses and economic strain. The parasite infests wounds and can quickly escalate into severe animal health issues if untreated.
Through long-standing binational programs, the U.S. and Mexico eliminated NWS decades ago, and continued surveillance has kept it contained further south. A detection this far north does not signal widespread risk, but it does serve as an important reminder of how quickly screwworm can move when livestock travel long distances.
Current Response and Monitoring
U.S. and Mexican authorities are coordinating closely to:
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Trace animal movements from Veracruz
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Conduct surveillance in surrounding herds and wildlife
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Increase communication with veterinarians and producers
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Assess risk at border regions
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Monitor for additional cases in commercial and non-commercial livestock
APHIS continues to operate the sterile fly barrier in Panama—the primary defense against northward movement of screwworm populations.
At this time, no evidence suggests spread beyond the two cases detected at the Nuevo León feedlot.
What Producers Should Watch For
Early identification remains the most effective tool against NWS. The parasite targets any open wound, including castration sites, navels of newborn calves, branding areas, and other untreated skin injuries.
Producers are encouraged to watch for:
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Wounds that fail to heal normally
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Foul-smelling or rapidly worsening lesions
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Visible maggot activity
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Swelling or discharge
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Animals showing signs of irritation, restlessness, or isolation
If screwworm is suspected:
👉 Contact a veterinarian and state or provincial animal health authorities immediately.
Proper diagnosis is essential to trigger appropriate response measures.
Livestock Movement: The Key Risk Factor
Both recent detections were linked to cattle transported from southern Mexico. This reinforces what officials have emphasized for decades:
Livestock movement poses the greatest risk for NWS spread.
Producers can reduce risk by:
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Observing newly received cattle closely during the first week
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Treating and monitoring any wounds or skin damage
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Keeping records of animal origins and travel routes
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Reporting abnormalities promptly
Surveillance works best when both government agencies and producers participate actively.
Texas and the U.S. Remain Free of the Pest
Despite the detection in Mexico, Commissioner Miller stressed that Texas’ cattle industry remains unaffected. He also highlighted the strength of long-standing eradication and monitoring programs that continue to protect the region.
“Texas ranchers are the backbone of American agriculture,” Miller noted. “We will protect our livestock, safeguard our economy, and do everything possible to keep the New World screwworm at bay.”
Where to Find More Information
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USDA Screwworm Information: Screwworm.gov
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Texas Department of Agriculture Updates: Texas Agriculture website
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Veterinary guidance: Consult your herd veterinarian for wound-care and monitoring protocols
Bottom Line
The detection near the Texas border does not signal an outbreak, but it is a timely reminder of how crucial early detection and movement oversight are. Staying alert, monitoring animals, and reporting concerns quickly remain the best tools to keep North America screwworm-free.
