Two New Mexico detections confirmed Oct. 15, and a Pecos County, Texas, cattle case on Oct. 10 widen the outbreak map for ranchers, horse owners and pet owners across the Southwest.

New Mexico agriculture officials confirmed on Thursday, Oct. 15, that a horse and a calf in Grant County are infested with New World screwworm, the state's third and fourth cases of the parasite whose larvae feed on living tissue, Source New Mexico reported. Both animals are in the same southwestern county where the state's second case, also a horse, was found in September.

The detections bring the U.S. animal total to 56 since June, with 52 in Texas and four in New Mexico, according to the Texas Public Radio tracker built on U.S. Department of Agriculture data. Another case was confirmed Oct. 10 in cattle in Pecos County, Texas.

Developing Story Note: This report covers new developments involving New World screwworm detections in New Mexico and Texas. Information may change as USDA, the New Mexico Livestock Board, the New Mexico Department of Agriculture and the Texas Animal Health Commission release additional findings. Latest verified update: New Mexico's announcement on Oct. 15, 2026, and the TPR tracker update of Oct. 15, 2026. USDA's Current Status page was last modified Oct. 14, 2026. Case data are through Oct. 15, 2026.

The practical effect is local and immediate — each confirmed case triggers an infested zone with a minimum radius of 12.4 miles around the animal's location, and New Mexico has now combined its most northern zones into one. Inside those zones, animal movement is restricted while officials expand surveillance and fly-trapping.

Grant County Becomes New Mexico's Hot Spot

New Mexico's first case appeared in June in a Lea County dog, days after USDA confirmed the first U.S. detection in a calf in Zavala County, Texas, on June 3. Grant County then logged a horse case on Sept. 17. With a horse and calf now added, three of the state's four cases sit in the same county.

"Early detection and prompt reporting are critical to limiting the spread of this pest," New Mexico Secretary of Agriculture Jeff Witte said in a statement. State Veterinarian Dr. Samantha Holeck of the New Mexico Livestock Board said officials are working with state and federal partners to investigate the cases and watch for more infestations.

Nature World News previously reported on a screwworm case in a Brewster County dog when the national count stood at 53. Since then, three new detections have been confirmed in eight days, two of them outside Texas. That shifts the reader's question from whether pets in West Texas are at risk to how far the parasite is moving through Southwest ranch country.

USDA's dashboard listed 55 animal cases, five active and 50 inactive, before the Grant County calf was added. All 56 confirmed cases have involved domestic animals, and none has been confirmed in wildlife or feral animals. One wild screwworm fly was caught in a Brewster County surveillance trap on Sept. 25, a detection tracked separately from the animal count.

Ranchers, Horse Owners and Hunters Face New Rules

The greatest burden falls on livestock producers inside the new zones, especially those with newborn calves, recently branded or tagged animals, or horses with open wounds. Female screwworm flies lay eggs in wounds and natural body openings, and the larvae burrow deeper as they feed. Untreated infestations can kill an animal.

In Texas, restrictions remain in effect in portions of 12 counties, including Brewster, Crockett and Pecos, and animals cannot leave designated infested zones without prior authorization from the Texas Animal Health Commission. Texas has also been releasing zones that meet federal criteria, with new announcements posted Oct. 10 and Oct. 13 on USDA's screwworm status page.

Those rules translate into real costs: inspections before moving animals, extra wound treatments, more veterinary visits and possible delays during fall shipping. Hunters heading out this season are also being asked to inspect harvested game for unusual wounds and report anything suspicious.

The wider trade picture matters for New Mexico. USDA reopened the Douglas, Arizona, port to Mexican cattle on Aug. 24 and said it would then consider reopening the Santa Teresa and Columbus ports in New Mexico, depending on Mexico's progress and any change in risk in Sonora or Chihuahua. USDA has not said whether the new Grant County cases affect that timeline.

Spotting a Screwworm Wound Before It Spreads

Owners should look for wounds that worsen instead of healing, thick or foul-smelling drainage, swelling around an injury, visible larvae moving in a wound, and signs of pain or restlessness. Speed matters — the earlier a case is reported, the sooner crews can trap flies and release sterile ones nearby.

USDA urges anyone who finds suspicious wounds or maggots in animals or people to "report it immediately." In New Mexico, that means calling the New Mexico Livestock Board or a veterinarian; the state also runs a tracking website. In Texas, suspected livestock cases go to the Texas Animal Health Commission, which posts an address lookup for infested zones.

Do not move an animal with a suspicious wound before a veterinarian examines it. Human infestations are rare, and USDA does not consider screwworm a food safety threat because the larvae feed on living animals rather than meat bound for consumers. Anyone who finds larvae in their own wound should seek medical care.

Screwworm Outbreak Timeline

Oct. 15, 2026: New Mexico confirms cases in a Grant County horse and calf, raising the U.S. total to 56.

Oct. 10, 2026: Cattle case confirmed in Pecos County, Texas.

Oct. 2, 2026: Dog case confirmed in Brewster County, Texas.

Sept. 25, 2026: First wild screwworm fly of the outbreak caught in a Brewster County trap.

Sept. 17, 2026: New Mexico's second case confirmed in a Grant County horse.

June 3, 2026: USDA confirms the first U.S. detection in a Zavala County, Texas, calf.

Several questions remain open: how the Grant County animals became infested, whether flies are established locally, and whether more cases will surface as trapping expands. Federal and state crews are continuing sterile fly releases, which collapse wild populations because females that mate with sterile males produce no offspring. The next data will come from USDA's dashboard and state announcements, and Nature World News will track any new zones or port decisions.

The bottom line: the outbreak remains concentrated in Texas, but New Mexico's Grant County is now a second front. Owners there should inspect wounds daily, report anything unusual quickly and follow movement rules rather than wait for a confirmed case next door.

What Readers Want to Know

How many screwworm cases are there in the U.S.?

There are 56 confirmed animal cases since June: 52 in Texas and four in New Mexico, as of Oct. 15.

Where are the newest cases?

A horse and a calf in Grant County, New Mexico, were confirmed Oct. 15, and cattle in Pecos County, Texas, were confirmed Oct. 10.

What is a New World screwworm?

It is the larva of a fly that lays eggs in open wounds or body openings of warm-blooded animals. The larvae feed on living tissue.

What signs should animal owners watch for?

Wounds that worsen, foul-smelling drainage, swelling, visible larvae, and unusual pain or restlessness.

Can people get screwworm or get sick from eating meat?

Human cases are rare. USDA does not consider screwworm a food safety threat.

Who should I call if I suspect a case?

Contact a veterinarian and the New Mexico Livestock Board or the Texas Animal Health Commission, depending on your state.