Two new cases of New World screwworm in southwestern New Mexico are raising concerns about the next planned reopening of the U.S.-Mexico border to cattle imports, potentially complicating efforts to restore livestock trade between the two countries.
State and federal animal health officials confirmed the infestations Oct. 15 in a calf and a horse in Grant County, near the Columbus, New Mexico, port of entry. Columbus had been identified as the next crossing expected to reopen to Mexican cattle, although USDA has not announced an official date.
The detections follow a previous case involving a horse in Grant County on Sept. 17, bringing New Mexico’s total to four confirmed animal cases since the parasite returned to the United States.
The new cases have prompted additional surveillance, animal movement restrictions and expanded fly-trapping efforts across southwestern New Mexico.
New infestations prompt movement restrictions
In response to the detections, the New Mexico Department of Agriculture and New Mexico Livestock Board established two infested zones in Grant County.
One surrounds Silver City, while the second is centered near Coyote Hills and includes the Lordsburg, Playas and Hachita valleys. The designated areas extend into neighboring Luna County, with a broader surveillance zone reaching east toward Columbus.
Animals within the infested zones are subject to mandatory inspections and may require treatment before being moved within or outside the restricted areas.
“We are working closely with our state and federal partners to investigate these cases, increase surveillance and monitor for additional infestations,” said State Veterinarian Dr. Samantha Holeck.
Officials have also increased fly trapping near the confirmed cases to determine whether additional screwworm activity is present.
The New Mexico Department of Agriculture is urging livestock producers, veterinarians and animal owners to closely inspect animals and report suspicious wounds.
“We appreciate the continued cooperation of livestock producers, veterinarians and animal owners as we respond to these additional cases,” said New Mexico Secretary of Agriculture Jeff Witte. “Early detection and prompt reporting are critical to limiting the spread of this pest. We encourage everyone to remain vigilant and work closely with animal health officials.”
Border reopening plans face new uncertainty
The latest cases come at a particularly sensitive time for cattle producers and livestock traders on both sides of the border.
USDA began reopening cattle crossings in phases on Aug. 24, starting with Douglas, Arizona. The Santa Teresa, New Mexico, crossing followed on Sept. 24, restoring access through one of the busiest livestock ports along the southern border.
Columbus was expected to be next in the reopening sequence.
Although no date had been formally announced, livestock traders had anticipated another reopening roughly 30 days after Santa Teresa, potentially placing Columbus on track for late October.
The new detections near the crossing could complicate that timeline as federal and state officials assess the risk of additional infestations.
No official postponement of the Columbus reopening has been announced in the reporting available as of Oct. 19.
For cattle producers, the uncertainty adds another challenge to cross-border livestock movement. Mexican feeder cattle are an important source of animals for U.S. feedlots, particularly in the Southwest, where imports support cattle feeding and beef production.
Restrictions on cattle crossings can affect feeder cattle availability, transportation logistics and marketing decisions for producers on both sides of the border.
U.S. screwworm cases reach 56
The latest New Mexico detections bring the total number of confirmed New World screwworm infestations in U.S. animals to 56 since June 2026, according to Texas Public Radio’s Oct. 15 report.
Texas accounts for 52 cases, while New Mexico has recorded four.
The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service had listed 55 confirmed animal cases, including five active and 50 inactive, before the additional New Mexico calf case brought the combined total to 56.
All confirmed U.S. animal infestations have involved domestic animals, with no confirmed cases in wildlife or feral animals as of that report.
Officials have also detected one wild screwworm fly in a surveillance trap in Brewster County, Texas, on Sept. 25. That detection is tracked separately from animal infestations.
New World screwworm is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals. Unlike common maggots, which generally feed on dead or decaying material, screwworm larvae can invade healthy tissue surrounding wounds.
Female flies lay eggs in open wounds or natural body openings, and infestations can rapidly worsen without treatment.
Cattle, horses, sheep, goats, wildlife and pets are all susceptible.
Producers should pay particular attention to wounds that fail to heal, unusual swelling, bloody or foul-smelling discharge, visible larvae and changes in animal behavior.
Prompt veterinary attention and reporting are essential to preventing additional infestations.
Federal and state officials continue using surveillance, movement controls and sterile-fly releases to combat the parasite.
For now, the latest detections underscore the challenges facing efforts to control New World screwworm while reopening livestock trade along the southern border. With Columbus next in line, the coming weeks could be critical for determining whether additional cattle crossings can resume operations as planned.