10 November 2026, Austin, US: Confirmed infestations of New World screwworm in the United States climbed to 116 across Texas, New Mexico and Arizona, with 56 cases still active, according to the latest US Department of Agriculture data cited by animal health officials this week. The count marks a nearly 47% increase from the figure reported the previous Sunday, underscoring how quickly the parasite has spread since detections accelerated in October.
The pest, a fly larva with the scientific name Cochliomyia hominivorax, burrows into the living tissue of warm-blooded animals and can kill an untreated host within one to two weeks. The United States eradicated screwworm decades ago using a sterile insect technique that flooded affected areas with lab-raised, sterilized male flies, but the parasite has persisted in parts of Central and South America and has been pushing north again this year.
Of the 116 confirmed cases, 114 involve livestock and pets, while two involve wildlife, elk found in Pecos and Jeff Davis counties in Texas, both now listed as inactive. No human infestations have been reported in the current US outbreak; the USDA and the Texas Animal Health Commission (TAHC) describe human cases as historically rare. Recent detections include cattle in Hudspeth and Mitchell counties in Texas, a horse in Greenlee County, Arizona, and horses, cattle and a dog in New Mexico. A wild screwworm fly was also caught this week in a surveillance trap in Otero County, New Mexico, one of several such wild-fly trap detections recorded since October.
Movement restrictions remain in place
Animal movement restrictions remain in effect across parts of 16 Texas counties, Brewster, Crockett, Culberson, Edwards, El Paso, Hudspeth, Jeff Davis, Pecos, Presidio, Reeves, Schleicher, Starr, Sutton, Terrell, Val Verde and Zapata, along with affected areas of New Mexico and Arizona. Officials caution that reclassifying a case as inactive does not mean the surrounding area is free of the parasite, since testing and monitoring continue in those zones.
TAHC and USDA have expanded surveillance, stepped up monitoring of animal movement and urged ranchers, pet owners and veterinarians to report suspected cases quickly. The US Food and Drug Administration has authorized several medications for use in dogs and cats, including the over-the-counter flea and tick products Capstar and nitenpyram, as part of the broader response. The public is being asked to check animals regularly for unusual wounds, visible larvae or sudden behavioral changes that could signal infestation.
The outbreak has also renewed attention on border infrastructure built to contain the pest. USDA announced earlier this year the completion of a sterile fly dispersal facility in Edinburg, Texas, intended to breed and release sterile male flies near the border to push back the parasite’s northward spread and protect the US cattle industry. Mexico has also reported rising numbers of screwworm cases in livestock, concentrated in its southern states closest to the outbreak’s Central American source. USDA suspended livestock imports from Mexico at the southern border in May 2025 after a rise in cattle infections there, a restriction officials have eased and reimposed intermittently as case counts in Mexico have fluctuated.
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