On September 15, 2026, the U.S. Department of Agriculture announced that a horse in Presidio County, Texas, tested positive for the New World screwworm, marking the first confirmed infection of this parasitic fly in a Texas horse.
The New World screwworm is a fly whose larvae feed on the tissue of warm‑blooded animals. Infestations can cause severe wounds, secondary infections, and can be fatal if untreated. The parasite has historically affected cattle, sheep, and goats, and it is a regulated animal health concern because of its potential to spread rapidly among livestock.
The USDA's detection of the organism in a single horse triggers a response under existing animal health protocols. Officials will likely conduct follow‑up testing of nearby animals, implement quarantine measures as needed, and coordinate with state veterinary services to contain any further transmission. The agency emphasizes that early identification is critical to preventing broader outbreaks.
While the case involves only one horse, the finding underscores the need for continued surveillance of screwworm activity across Texas. Ranchers and horse owners are advised to monitor animals for signs of infestation, such as open wounds with maggot development, and to report any suspicious cases to veterinary authorities promptly.
The detection arrives as part of the USDA’s ongoing national surveillance for screwworm, a program that routinely samples livestock in regions where the parasite is known to occur. Texas has previously reported infestations in cattle and small ruminants, but no horse cases have been documented until now. By confirming the parasite in a single equine host, officials can target control efforts to prevent spillover into other animal populations.