Texas Confirms First US Horse Case of Flesh-Eating Screwworm Since 1960s Eradication

A working ranch horse in Presidio County, Texas tested positive for New World screwworm on September 9, according to the US Equestrian Federation. The USDA confirmed the case on September 10. It is the first horse infected with the flesh-eating parasite in the United States this century, according to reporting from equimanagement, Horse&Rider, and EQUUS Magazine, all citing the same US Equestrian Federation statement.

The parasite was found in the horse's hind limb wound, according to the federation. New World screwworm isn't a worm at all. It's the larvae of blow flies that burrow into living tissue, feeding on open wounds until they cause severe tissue damage, secondary infection, and death if untreated, according to BloodHorse and equimanagement.

The Texas Animal Health Commission responded immediately by issuing an order Wednesday that bans the movement of warm-blooded animals outside a designated infested zone covering parts of Presidio and Jeff Davis counties, according to KSL News and The Guardian.

A Parasite the US Already Beat Once

The US eradicated screwworm in the 1960s and pushed it back to Panama through decades of control efforts, according to equimanagement. It stayed gone for over 60 years.

The USDA began reporting cases in early June 2026, starting with a calf in Zavala County near the US-Mexico border, according to The Guardian. The parasite had already spread through Mexico before reaching Texas soil.

Since then, cases have piled up in cattle, goats, sheep, and one dog in New Mexico, before finally showing up in a horse, according to equimanagement. The USDA's case count through August put the total at 49 animals this year, with all but one in Texas, according to The Guardian.

The numbers show an outbreak that hasn't been crushed but also hasn't exploded: 30 cases in June, 14 in July, and just 3 in August, according to the Epoch Times, citing USDA data current through August 25.

Texas Governor and Federal Response

Texas Governor Greg Abbott issued a disaster proclamation in June to free up state resources for the fight, according to The Guardian. Before any case was even confirmed on US soil, the Trump administration had already announced a sterile fly dispersal facility in Edinburg, Texas, designed to flood the population with sterilized male flies whose offspring won't survive, according to The Guardian.

On the drug front, the FDA granted emergency use authorization on August 27 for Bimectin, a generic ivermectin injection from Ireland-based Bimeda Animal Health, for preventing screwworm in cattle within 24 hours of birth, according to the Epoch Times. It's a generic version of Ivomec, which the FDA authorized back in February. FDA Center for Veterinary Medicine director Timothy Schell said the move ensures "producers aren't dependent on a single manufacturer or product to protect their herds."

The drug can't be used in lactating dairy cows or calves destined for veal, and the FDA based its safety conclusions on studies from Brazil and Argentina dating to the 1990s plus a 2019 Brazilian study, according to the agency's fact sheet cited by the Epoch Times.

Economic Impact and Uncertainties

Experts estimate a widespread outbreak could cost the Texas economy up to $1.8 billion, according to KSL News. A screwworm infestation can wipe out livestock herds fast, and the disaster declaration shows officials are treating this as an economic threat.

Reuters reported last week on growing concerns that smuggled animals, including horses, could be possible hosts helping the parasite cross into the US, according to KSL News. Neither the USDA nor Texas authorities have said how this specific horse got infected, according to KSL News. No investigation into smuggling as the source of this case has been announced.

What Horse Owners Should Do

The US Equestrian Federation is telling owners to check horses daily for wounds, swelling, drainage, or foul odor, paying close attention to cuts, surgical sites, and moist areas like the nostrils and eyes, according to BloodHorse. Competition organizers now have protocols requiring wound checks at arrival and ongoing monitoring during events, per USEF guidance posted at usef.org/screwworm.

The open question now is whether containment in Presidio and Jeff Davis counties holds, or whether the parasite finds its way into more horses as it has in cattle, sheep, and goats over the summer. The USDA's next case update will show whether September looks more like August's trickle of three cases or June's surge of thirty.