A working ranch horse in Presidio County, in the Big Bend region of far West Texas, is the first equine case of New World screwworm in the 2026 incursion. The U.S. Equestrian Federation reported that the infestation was detected Sept. 9 on one of the horse's hind limbs, and KSAT reported Tuesday, Sept. 15, that the U.S. Department of Agriculture had confirmed the case. On Sept. 9, the Texas Animal Health Commission also issued a new movement order covering parts of Jeff Davis and Presidio counties.

The case arrives while the outbreak map is moving in two directions. Since Aug. 31, Texas has released or modified infested zones in Gillespie, Kerr, Kimble, La Salle, Webb, Uvalde, Zavala, Coke, Tom Green, Schleicher and Sutton counties. One of those releases covers Zavala County, where a calf became the first U.S. animal case of the current outbreak on June 3.

For horse owners, the practical meaning is immediate. Screwworm flies lay eggs in open wounds, and the commission warns that untreated animals can die within one week of infestation. Animals leaving an active infested zone must first be inspected and certified.

Active Zones Now Cover Parts of 16 Texas Counties

The Texas Animal Health Commission lists movement restrictions in parts of Bandera, Brewster, Crockett, Edwards, Jeff Davis, Jim Hogg, Medina, Pecos, Presidio, Schleicher, Starr, Sutton, Terrell, Uvalde, Val Verde and Zapata counties. Warm-blooded animals in those zones may not leave without prior authorization from the commission. Some counties appear on both the active and released lists because only parts of them were lifted. The commission reports cases on 39 premises across 17 Texas counties since the first detection.

Released zones drop screwworm-related movement requirements for livestock and pets inside those areas, but USDA noted that all interstate movement and international export requirements still apply.

Local reports of active cases differ, which is worth flagging. KVIA reported on Monday that there had been 49 animal cases, with two still active in a goat and a sheep in Val Verde County, according to USDA. On Tuesday, KSAT reported that USDA listed two active Texas cases, the Presidio County horse and a dog in Crockett County. The authoritative running tally is USDA's confirmed-detections dashboard, which the commission points to for individual case information.

Big Bend Horse Owners Face the Most Direct Risk

The equestrian federation's guidance is specific. Owners should inspect horses every day for wounds, swelling, drainage, foul odor, or maggots, paying close attention to small cuts, surgical sites, the umbilical area of foals, and moist areas such as the lips, nostrils, eyes, and genitals. Because the larvae feed on living tissue, the group stressed that "even small cuts or sores should be cleaned, protected, and checked closely" until they heal. Fly masks, sheets, clean stabling and veterinarian-recommended fly control can limit exposure.

The federation also has protocols for licensed competitions, which may include wound checks on arrival and monitoring during an event. State animal health officials, however, set the rules for animals within their states and for animals coming from affected zones.

Ranch horses and livestock in and near the active zones carry the greatest exposure right now, along with any animal with a fresh wound, newborns, outdoor pets, and wildlife. Moving animals out of a zone takes time and paperwork. Owners must schedule an inspection with the commission or a certified inspector, who completes a movement and treatment certificate listing the product used and the animals' official identification.

A New Species in the Texas Outbreak

Nature World News previously reported on three FDA screwworm drug authorizations, including the first injectable product listing deer. Since then, the Texas outbreak has produced its first equine case in a new corner of the state, while several earlier zones have met the federal criteria for release.

The broader outbreak is large. As of its Aug. 11 update, the CDC reports that Central American countries and Mexico have logged more than 209,400 animal cases and more than 2,500 human cases. There have been no reports of human infestations acquired in the United States, and the agency rates the risk to people here as very low. The only U.S. human case since the pest's return to the region was confirmed in August 2025 in a person who had traveled to El Salvador. USDA says the outbreak is not a food safety issue, and the commission notes that federal meat inspection is designed to keep affected product out of commerce.

Sterile flies remain the core eradication tool. USDA says its investments will bring production to approximately 500 million sterile flies per week, the same volume used to eradicate the pest from the United States decades ago. The United States last eradicated screwworm in 1966.

Key questions remain open. Officials have not publicly described how the horse became infested or whether flies are established around the Presidio County premises.

Steps for Texas Animal Owners This Week

Before moving any animal, owners should check the commission's zone map. Suspected cases in livestock and companion animals can be reported to a commission region office or its veterinarian-on-call line at 1-800-550-8242, and pet owners should also contact their own veterinarian. Suspected wildlife cases go to Texas Parks and Wildlife at 512-389-4505. Anyone who sees or feels maggots in a wound on their own body should contact a health care provider immediately and should not try to remove them.

Keeping wounds clean and covered is the single most useful habit for livestock, pets and people alike. Residents outside the affected areas do not need to take special action.

Further changes will come through commission orders as zones meet release criteria and through USDA dashboard updates. Nature World News will track the Presidio County case, any new zones, and changes in sterile fly production. For now, risk to people remains very low, but West Texas horse owners should begin daily wound checks.

Timeline of Key Developments

Sept. 15, 2026: KSAT reports that USDA lists two active Texas cases, including the Presidio County horse.

Sept. 9, 2026: The first equine case is detected, and the commission issues an order for Jeff Davis and Presidio counties.

Sept. 4, 2026: Texas modifies and partly releases a zone in Kimble, Schleicher and Sutton counties.

Aug. 31 to Sept. 3, 2026: Texas releases its first eligible infested zones.

June 3, 2026: USDA confirms the first U.S. animal case of the current outbreak, a calf in Zavala County.

What Readers Want to Know

What is new in the Texas screwworm outbreak? A Presidio County ranch horse became the first equine case of the 2026 incursion, detected Sept. 9, and the state issued a new movement order the same day.

Which counties have active restrictions? Parts of 16 counties, including Presidio, Jeff Davis, Brewster, Val Verde, and Crockett. The commission's zone map shows exact boundaries.

Is screwworm dangerous to people? It can infest people, but the CDC rates U.S. risk as very low and reports no locally acquired human cases.

How can horse owners protect their animals? Inspect horses daily, clean and cover wounds, use fly masks or sheets, and call a veterinarian at the first sign of maggots.

Can I move animals out of an infested zone? Only with prior authorization, which requires an inspection and a movement and treatment certificate.