New World Screwworm Update: 53 Animal Cases in Texas and New Mexico, and What Pet Owners Should Check

As of October 4, 2026, USDA had confirmed 53 New World screwworm cases in animals in the United States: 51 in Texas and 2 in New Mexico. The first was a three-week-old calf in Zavala County, Texas, confirmed on June 3, the first U.S. detection in decades. Three cases were active on October 4: a dog in Brewster County confirmed October 2, goats in Crockett County confirmed September 26, and a horse in Grant County, New Mexico, confirmed September 17. Separately, a wild screwworm fly turned up in a surveillance trap in Brewster County on September 25. Trap finds are tracked on their own and aren't counted as animal cases.

Why screwworm isn't an ordinary maggot problem

The screwworm is the larva of a fly, Cochliomyia hominivorax. The female lays her eggs in an open wound or a natural body opening, and the eggs hatch within hours. Ordinary blow fly maggots feed on dead or decaying tissue; screwworm larvae eat living flesh, so the wound keeps getting bigger and often becomes infected. Left untreated, an infestation can kill the animal. Our New World screwworm profile covers the fly's biology and history.

Where the response stands

USDA says it has released more than 1 billion sterile flies in Texas since February and aims to raise production to 500 million flies a week by next summer. The method is the one that eradicated screwworm from the U.S. decades ago: a female usually mates only once, so a female that mates with a sterile male lays eggs that never hatch, and the wild population collapses. Around each confirmed case, USDA and the Texas Animal Health Commission set a 20-kilometer infested zone with quarantines, movement controls and extra surveillance.

Agriculture Secretary Brooke Rollins has said officials are making progress but that the threat hasn't passed, especially for Arizona and New Mexico. Southern ports of entry are still closed to livestock from Mexico, apart from a first phased reopening: USDA reopened the Douglas, Arizona, port to livestock from Sonora on August 24, 2026, and says it will consider the Santa Teresa and Columbus, New Mexico, ports after evaluating that step. In late July USDA also announced $25 million for a new sterile fly dispersal facility in Arizona.

What pet and livestock owners should do

For most people, nothing about daily life changes. The risk is to livestock, pets and wildlife, and screwworm is not a food safety issue: the larvae feed on living tissue in wounds, and inspection keeps infested animals out of the food supply. The sterile flies being released are safe for people, pets, livestock and wildlife, according to USDA.

If you live in or travel through West or South Texas, New Mexico or Arizona with animals, check them for:

• wounds that get worse instead of healing, including fresh surgical or injury sites
• bloody, thick or foul-smelling drainage, or swelling around a wound
• maggots moving inside a wound
• signs of pain or restlessness

Call your veterinarian right away if you see any of these, and don't move the animal until it has been examined. In Texas, suspected livestock cases go to the Texas Animal Health Commission's veterinarian on call (1-800-550-8242), and wildlife cases to a Texas Parks and Wildlife Department biologist. Infestations in people are rare; USDA advises anyone with a suspicious sore to get medical care promptly.

What to watch next

The numbers to follow are new cases outside the current Texas and New Mexico clusters, any detection in Arizona, and whether the phased port reopenings continue. USDA posts confirmed detections on its screwworm dashboard, and we'll update our screwworm profile as the status changes.