New World Screwworm

The USDA has confirmed a case of New World Screwworm (NWS) in a leg wound on a working ranch horse in Grant County, New Mexico. This is the second confirmed horse case in the United States as part of the current incursion. A map showing the infested zone related to this case is available here , and additional guidance from New Mexico animal health officials is available here . US Equestrian continues to monitor the progression of NWS in the United States and reminds you that fly migration and...

On September 9, 2026, the first equine case of New World Screwworm (NWS) as part of the 2026 incursion was detected on a hind limb of a working ranch horse in Presidio County, Texas. NWS is a serious parasite that can infest wounds in horses and other warm-blooded animals. Because the larvae feed on living tissue, even small cuts or sores should be cleaned, protected, and checked closely until they are fully healed. Horse owners should inspect their horses every day for wounds, swelling,...

On June 3, 2026, the U.S. Department of Agriculture confirmed New World Screwworm in the umbilical area of a calf in Zavala County, Texas. This expansion into the United States is alarming and US Equestrian wants to make sure you know about the potential risks of this parasitic fly to horses. What is the risk of screwworm to horses? Screwworm myiasis (infestation) is caused by fly larvae (maggots) that feed on living tissue of any warmblooded animal. Horses, cattle, wildlife, pets, and...

On September 21, 2025, the United States Department of Agriculture announced the confirmation of a New World Screwworm (NWS) case in Nuevo Leon, Mexico, less than 70 miles from the U.S.-Mexico border. This new case is located near a major highway from Monterrey, Mexico to Laredo, Texas, one of the most heavily trafficked commercial thoroughfares in the world. Screwworm was once eradicated from the United States and potential incursion threatens the equine industry. Why is Protecting the United...