New Screwworm Case Hits New Mexico Horse. USDA Reopens Major Cattle Port Anyway

A horse in the remote Mimbres area of Grant County, New Mexico tested positive for New World screwworm on Thursday, September 17, according to the U.S. Department of Agriculture. It's New Mexico's second confirmed case since the parasite returned to the U.S. this summer, and it landed on the same day Agriculture Secretary Brooke Rollins announced the Santa Teresa port of entry, roughly 150 miles away in Doña Ana County, will reopen to Mexican cattle imports on September 24, according to Bloomberg and TT News.

Santa Teresa isn't a minor crossing. It's the busiest livestock port on the southern border, handling nearly 500,000 cattle in 2024 alone, about 40% of all U.S. cattle imports from Mexico, according to USDA figures cited by TT News. It's been closed for more than a year specifically because of the screwworm threat, according to Searchlight New Mexico and Yahoo News.

What officials are saying

Dr. Samantha Holeck, the state veterinarian with the New Mexico Livestock Board, said the Grant County case is not expected to delay the port reopening. She told Searchlight New Mexico that officials are still investigating how the horse got infected, since the animal hadn't recently traveled from the region. "At this point, there are still really a lot of unknowns, but we are working to collect as much information as we can, as fast as we can," Holeck said.

Rollins, speaking at the same September 17 press conference where she announced the reopening, acknowledged the parasite hasn't been eradicated. She said the agency will delay the move if "we're not 100% sure in the safety and the protocols," according to TT News. She's also eyeing a second reopening, at the Columbus, New Mexico port, if containment holds.

The numbers officials are leaning on: 50 total U.S. screwworm cases confirmed since the outbreak began in June, almost all in Texas, with only three currently active, according to TT News and Bloomberg. Compare that to nearly 2,000 active cases across Mexico's border states of Sonora, Chihuahua, Coahuila, Nuevo León and Tamaulipas, per Searchlight New Mexico.

The case for caution

A new domestic case just showed up in a county where the infected animal hadn't traveled, meaning the source is unknown, and officials opened the door to hundreds of thousands more cattle crossings 150 miles away on the same day. Newsquawk's market analysis notes that screwworm detections near the border have historically triggered animal movement restrictions and even outright import suspensions while containment gets sorted out. This time, the response is expansion rather than restriction.

This logic mirrors USDA's own reasoning when it kept Santa Teresa closed for over a year in the first place. The agency's own containment argument—three active U.S. cases against nearly 2,000 in Mexico, plus a horse infection with an unknown source—presents a real tension USDA hasn't fully resolved publicly. Holeck's own words, "still really a lot of unknowns," underscore that the investigation into how this horse got infected isn't finished.

Against that, USDA points to a buildout of containment infrastructure: a completed sterile fly dispersal facility and a sterile fly production facility near the southern tip of Texas, plus a planned dispersal site in Arizona, according to Searchlight New Mexico. The FDA has also issued emergency use authorizations for screwworm prevention and treatment drugs. USDA Under Secretary Dudley Hoskins pointed to cleared zones in Texas's La Salle, Webb, Gillespie, Kerr and Kimble counties as proof the response is working, according to Breitbart.

The count keeps moving

Case totals are a moving target across these reports. Breitbart put the tally at 48 Texas cases plus New Mexico's dog case, using slightly older data, while Bloomberg and TT News count 50 total as of September 17, which appears to include the new Grant County horse. Breitbart also flagged a horse infestation in Presidio County, Texas, calling it the first screwworm case in a Texas border county "this century," a separate incident from the New Mexico case.

Texas Agriculture Commissioner Sid Miller warned back in February that a mild winter meant screwworm flies were staying active farther north than usual, telling Breitbart Texas at the time, "this will impact everybody in some form." Seven months later, his warning about spring and summer spread has largely played out, just not at the scale some feared.

The Santa Teresa reopening is set for September 24. New Mexico livestock officials haven't said when their investigation into the Grant County horse will produce answers, and hunters statewide have been asked by the state Department of Game and Fish to report any wounded animals with maggots or egg packets, since screwworm doesn't care whether its host is livestock or wildlife.