Confirmed New World screwworm infestations in the United States have climbed to 116 across Texas, New Mexico and Arizona, 56 of them still active, according to the latest US Department of Agriculture data cited by animal health officials. The count is nearly 47% higher than the figure reported a week earlier.
The screwworm, Cochliomyia hominivorax, is a fly whose larvae burrow into the living tissue of warm-blooded animals and can kill an untreated host within one to two weeks. The US eradicated it decades ago by releasing sterilised male flies, but the parasite survived in parts of Central and South America and has been moving north again this year.
Of the 116 cases, 114 involve livestock and pets and two involve wildlife, elk found in Pecos and Jeff Davis counties in Texas, both now inactive. No human cases have been reported. 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, and a wild screwworm fly was caught in a surveillance trap in Otero County, New Mexico.
Animal movement restrictions cover parts of 16 Texas counties, among them Brewster, El Paso, Hudspeth, Pecos, Presidio, Starr, Val Verde and Zapata, and affected areas of New Mexico and Arizona. Officials stress that an inactive case does not mean the surrounding area is free of the parasite.
The Texas Animal Health Commission and USDA have widened surveillance and movement checks and asked ranchers, pet owners and veterinarians to report suspicious wounds, visible larvae or sudden changes in behaviour quickly. The US Food and Drug Administration has authorised several medicines for dogs and cats, including the over-the-counter flea and tick products Capstar and nitenpyram.
USDA completed a sterile fly dispersal facility in Edinburg, Texas, earlier this year to release sterile males near the border. Mexico is also reporting more cases in its southern states, and the US suspended livestock imports from Mexico in May 2025, a restriction since eased and reimposed several times as Mexican case numbers changed.
Photo: John Kucharski / Wikimedia Commons (Public domain)
Source: Global Agriculture
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