Screwworm has reached four U.S. horses, and October cases are up to 22 from 3 in September

New World screwworm is spreading faster through U.S. domestic animals, and horses are among them. In a release dated October 30, US Equestrian (USEF) said October had already produced 22 cases in domestic animals, up from three in September and 14 in July. The same release says four horses have been confirmed since the first equine detection on September 9.

The figures below are USEF's, as published on October 30. USDA's own case page refused our automated request, so we could not check the numbers against it today. The USDA page is the place for current counts by state.

What USEF reported

• Arizona: federal and state officials confirmed the state's first case, maggots in a wound on a domestic dog in Cochise County, according to USEF citing Arizona officials.
• Where infestations are active: USEF's screwworm page lists Arizona, New Mexico and Texas.
• Mexico: 1,959 active cases, 113 of them in horses, per USEF.
• Horses: the first U.S. equine case was a working ranch horse in Presidio County, Texas, with the parasite in a hind limb, KSAT reported on September 15. On September 22 USEF reported a second, a ranch horse with a leg wound in Grant County, New Mexico.

Dr. Katie Flynn, USEF's senior staff veterinarian, said that while the count "still sounds small," the group is concerned about the increase.

What owners are told to do

USEF's guidance is daily inspection for wounds, swelling, drainage, foul odor or maggots. It names small cuts, surgical sites, a foal's umbilical area and moist spots such as lips, nostrils, eyes and genital areas. Anyone who sees maggots or anything unusual in a wound should call a veterinarian right away. Suspected cases must be reported to state and federal animal health officials. Beyond that, we are not offering treatment advice: call your veterinarian.

What it means for showing and shipping

A horse that lives in or has been in Texas, New Mexico or Arizona needs to be checked against the USDA "infested zone," a 20-kilometer perimeter around infested premises. USEF says horses from those zones coming to USEF-licensed shows may have to be checked for wounds on arrival and monitored through the competition. State animal health officials set their own entry rules, so owners shipping across state lines should check both the origin and destination state. USEF's protocols are at usef.org/screwworm.

For show managers, USEF's page points to a larger risk than one sick horse: infestation on the grounds and the quarantine that could follow. See our equestrian calendar for upcoming events and check each organizer's page for any health requirements.

What we could not confirm

USEF's page says screwworm was confirmed in the United States on June 3, 2026, while its October release compares October with July, "when NWS was first detected in the United States." We have not reconciled the two. We also could not confirm any equine case after the four USEF counts, or the count for August.

Sources: US Equestrian press release of Oct. 30, 2026 and screwworm page; KSAT, Sept. 15, 2026. Case counts are as published by US Equestrian and may have changed. This is information, not veterinary advice.