New World Screwworm in Horses: 2026 Texas, New Mexico, Arizona Cases

New World screwworm in horses: what just happened

Update (2026-11-03): New World screwworm in horses, an infestation of flesh-eating fly larvae in a wound, has now been confirmed in a third state. On Nov. 2, the Arizona Department of Agriculture confirmed it in a domesticated horse near Hereford in Cochise County, a horse with no known travel history.

The horse is about 45 miles from Arizona's first case, a dog on a ranch near Elfrida, also in Cochise County. A local vet examined the dog on Oct. 26, and USDA confirmed the case on Oct. 28.

A mandatory 12.4-mile (20 km) infested zone now surrounds the horse's property. No animal may leave it unless a state veterinarian has inspected it and authorized the move, and self-inspection is suspended while the zone is active. USDA is releasing sterile flies in the surrounding area and building a sterile fly dispersal facility in Douglas, Arizona.

Before Arizona, US Equestrian had counted four U.S. horse cases since Sept. 9, according to its Oct. 30 update. Those included a working ranch horse in Presidio County, Texas, and two ranch horses in Grant County, New Mexico; the release didn't say where the fourth was. The Texas horse was found on Sept. 9 with a wound on one hind leg, and US Equestrian called it the first equine screwworm case in the United States this century. The first New Mexico horse, near Mimbres, was identified on Sept. 17 with a leg wound, and a second Grant County horse was confirmed on Oct. 15, along with a calf.

The risk is concentrated in parts of Texas, southwest New Mexico and now southeastern Arizona, but anyone who hauls through the region, or buys horses from it, should know the signs. If you see a wound that won't heal, maggots, foul discharge or unusual irritation, call your vet or your state's animal health officials and don't move the animal.

For scale, Houston Public Media's case tracker counted 50 confirmed U.S. cases as of Sept. 21. By Nov. 2, Texas Public Radio's tracker, based on federal data, counted 90 animal cases across Texas, New Mexico and Arizona since June, including the Cochise County horse; 33 were active and 57 inactive. In October, USDA also confirmed the first U.S. wildlife case: an elk taken by a hunter in Pecos County, Texas.

What is New World screwworm?

Despite the name, it isn't a worm. New World screwworm (Cochliomyia hominivorax) is the maggot of a fly, and unlike most maggots it eats living tissue, not dead tissue.

The life cycle explains why owners need to move fast:

1. A female fly lays a cluster of eggs, up to several hundred at a time, at the edge of a wound or on moist membranes like the eyes and nostrils.
2. The eggs hatch within 10 to 12 hours.
3. The larvae feed for about a week, tearing deeper into the flesh with hooked mouthparts. Rings of tiny spines give them their screw-like look.
4. They drop to the ground, pupate and become new flies, ready to find the next wound.

A small cut that looked fine on Monday can be an active infestation by midweek. The flies don't pick a species, either: cattle, horses, dogs, wildlife and people can all be infested.

The United States wiped out screwworm decades ago by releasing sterile flies, and the same method is in use now. In June, Agriculture Secretary Brooke Rollins told senators USDA had invested about $1.3 billion against the pest since January 2025, and by September the government had released its billionth sterile fly in Texas, CNN reported. After Arizona's first case, about a million sterile flies were released around Cochise County, KJZZ reported.

Screwworm symptoms in horses: where and what to check

The first two U.S. horse cases, in Texas and New Mexico in September, both involved leg wounds, but flies go after any wound or moist opening. Build a quick daily check into feeding time or grooming.

Where to look

• Legs: cuts, scrapes, wire wounds and rubs, including the small ones you'd normally ignore
• Surgical sites: castration incisions and any stitched or healing wound
• Foals: the navel (umbilical area), every day
• Moist areas: eyes, nostrils, lips, sheath or udder, and under the tail

Warning signs

• A wound that gets bigger, deeper or wetter instead of healing
• A foul smell, or fluid draining from the wound
• Visible maggots in or around the wound
• Swelling around a wound
• The horse licking, biting or rubbing at one spot, or acting unusual around it

You can't reliably tell screwworm from ordinary blowfly maggots by eye. Lab confirmation relies on features you'd need a microscope to see, so treat any maggots in a living horse's wound as a vet call.

The 2-minute wound check

1. Check at the same time every day, so a change jumps out.
2. Run your hands down every leg, feeling for heat, swelling or wet, sticky spots.
3. Look at the eyes, nostrils and lips.
4. Check the belly, sheath or udder, and under the tail.
5. Take a dated phone photo of any wound so you can compare tomorrow.

Our health basics page covers normal vital signs, which help when you describe a problem to your vet.

Found maggots in a wound? Who to call

1. Call your veterinarian right away. Don't wait a day to see if it improves. Your vet reports suspected cases to state animal health officials.
2. Keep the horse where it is. Don't haul it anywhere until your vet or state officials say so.
3. Don't treat the wound yourself. Screwworm treatment uses products authorized for it, chosen by your vet. If officials ask you to collect larvae for testing, follow their instructions exactly.
4. Photograph the wound and check your other animals, including dogs, the same day.

Reporting contacts

• Texas: your Texas Animal Health Commission (TAHC) region office, or TAHC's reporting line at 1-800-550-8242
• New Mexico: the New Mexico Livestock Board, state veterinarian's office (505) 841-6161, or ScrewwormNM.org
• Arizona: the Arizona Department of Agriculture, diseasereporting@azda.gov or 602-542-4293 (weekdays, 8 a.m. to 5 p.m.); for wildlife, Arizona Game and Fish at 623-236-7201
• Other states: your veterinarian, who contacts your state veterinarian and USDA APHIS
• People: if you find maggots in your own wound, see a healthcare provider

Horse travel restrictions: screwworm rules for hauling and shows

Zones are drawn, redrawn and released often. Check the rules the day before you haul, not the week before.

Texas

All warm-blooded animals in a Texas infested zone need TAHC authorization before leaving. Expect an inspection and an NWS movement and treatment certificate listing the product used and the animal's official ID; inspection requests go to 512-714-1936. As of early November, TAHC listed zones covering parts of Brewster, Crockett, Culberson, Edwards, El Paso, Hudspeth, Jeff Davis, Jim Hogg, Pecos, Presidio, Reeves, Schleicher, Starr, Sutton, Terrell, Val Verde and Zapata counties.

New Mexico

Each confirmed animal's location gets an infested zone with a minimum radius of 12.4 miles (20 km). In the Oct. 15 update, the two northernmost zones were combined, leaving two separate infested zones at that point, and officials expanded surveillance and fly trapping around the affected sites. Animals inside an infested zone must be inspected, and treated if needed, before moving within or out of it. Zones can change after new cases, so check ScrewwormNM.org for current maps. Beyond that, officials said earlier that routine trips to the vet, fairs, sales or recreational rides generally aren't restricted unless an inspector flags a higher-risk situation, such as an open wound.

Arizona

The Nov. 2 infested zone has a mandatory 12.4-mile (20 km) radius around the Hereford horse's property. Livestock, horses and pets can't leave it unless a state veterinarian has inspected them and authorized the move. Self-inspection is suspended while the zone is active, so your own wound check doesn't clear a horse to travel. Arizona's first zone, around the Elfrida dog case, also has movement controls.

If you keep horses near Hereford, Bisbee or Elfrida:

• Check the Arizona Department of Agriculture's map of cases and infested zones before every trip, because zones can be added or redrawn.
• If your barn is inside a zone, contact the department before you load up and ask how to get an inspection. Don't haul out on your own.
• Keep up daily wound checks, and report anything suspicious to diseasereporting@azda.gov or 602-542-4293.

Other states and the border

Georgia's entry rules started on Sept. 21 with five New Mexico counties (Catron, Hidalgo, Luna, Sierra and Grant) and have since widened. Georgia's screwworm page now covers animals from Texas, from New Mexico and from the Arizona counties of Cochise, Graham, Greenlee, Pima and Santa Cruz. Animals from outside an infested zone in those areas need a certificate of veterinary inspection, issued within 7 days of travel, stating the animal was inspected and found free of screwworm. Animals coming from an infested zone need a Georgia entry permit, requested at least 48 hours ahead, and must follow the national screwworm movement guidance. Other states can add rules quickly, so call the destination state veterinarian's office before you go. Horse exports from the U.S. to Mexico have resumed: after negotiations between USDA and Mexican animal health officials, the Texas Department of Agriculture reopened the Del Rio Livestock Export Facility to horses going to Mexico for reproduction, sport, exhibition, work or transit, and Spectrum News reported in early October that horses were crossing again. Horses from or traveling through an infested zone may need extra inspection and treatment. Horse imports from Mexico have also restarted on a limited basis: on Oct. 26, USDA resumed equine imports by land through Santa Teresa, New Mexico, only. Horses must go through inspection and treatment before export, then a seven-day quarantine at a USDA-approved facility on the U.S. side of the border, so confirm current protocols with USDA before planning an import. Cattle imports from Mexico are restarting port by port: Douglas, Arizona, reopened on Aug. 24, Santa Teresa on Sept. 24 and Columbus, New Mexico, on Oct. 26, and USDA plans to reopen Nogales, Arizona, on Nov. 30 if conditions allow.

Shows and events

At US Equestrian-licensed competitions, horses coming from a screwworm infested zone with active cases must be checked for wounds on arrival before they can enter the stabling area, and that includes horses hauling in for the day. If you live in a state with a confirmed case, or your horse was in one in the past 14 days, then depending on the states involved, you may also need a documented veterinary inspection before you leave, on arrival, or both. If your horse has a wound, or a surgical incision a week old or less, bring vet records or a note on the health certificate showing it was treated with an FDA-authorized screwworm product.

Hauling checklist

• Current entry rules for your destination state
• Health certificate, current Coggins and any screwworm inspection paperwork
• Wound check before loading and again on arrival
• Fly mask and fly sheet for the trip
• Your vet's number and the state veterinarian's number saved in your phone

More on getting ready for events is in our show prep guide.

How to lower the risk in your barn

• Treat every wound promptly with your vet's guidance, and keep it clean and covered.
• Use vet-directed fly control plus physical barriers such as fly masks and fly sheets.
• Pick up manure often and get rid of standing water where flies breed.
• Fix what causes cuts: loose wire, protruding nails, broken boards. Our barn safety page has a walk-through.
• Ask about timing of elective procedures like castration if you're in or near a zone.
• Inspect new arrivals from Texas, New Mexico or Arizona the day they unload.

For the bigger daily routine, see our horse care guide.

What to watch next

• More Arizona cases and zones. Arizona's two cases came within a week of each other in Cochise County. Watch the Arizona Department of Agriculture's zone map, the sterile fly releases and progress on the Douglas dispersal facility.
• More New Mexico cases and zone changes. Officials are trapping flies and surveilling around the Grant County sites, and zones can be merged or redrawn. Texas has also been releasing some zones while adding others. Check TAHC's map and ScrewwormNM.org before any trip.
• More state entry rules. Georgia has already widened its entry rules to Texas, New Mexico and five southeastern Arizona counties, and more destination states may add requirements. Georgia's quick moves show destination rules can change within days of a new case.
• Border ports. Nogales, Arizona, is scheduled to reopen to Mexican cattle on Nov. 30 if conditions allow. Horse imports from Mexico run only through Santa Teresa for now, and USDA says it will consider other ports as conditions warrant.
• Fall show season. If your horse comes from an infested zone, expect a wound check on arrival, and build extra time into check-in.
• Warm days. Flies stay active while the weather is warm, so keep up daily checks until your vet says local risk has dropped.

Follow the latest horse news on our trends page.