The United States Department of Agriculture (USDA) confirmed the presence of New World screwworm (NWS) in a horse in Presidio County, Texas on September 10. According to the United States Equestrian Federation, NWS was discovered on the hind limb of a working ranch horse, marking the first equine case in the United States this century.
EDCC Health Watch is a marketing program of the Equine Network that utilizes information from the Equine Disease Communication Center (EDCC) to create and distribute verified equine disease reports. The EDCC is an independent nonprofit organization supported by industry donations to provide open access to infectious disease information.
About New World Screwworm
New World screwworm (NWS) is the larvae of blow flies (Cochliomyia hominivorax) that feed on the living tissue of horses and other warm-blooded animals. Adult flies do not bite and females lay their eggs in open wounds or mucous membranes. Clinical signs of NWS include painful wounds with maggots, tissue damage, foul odor, bacterial infection, reduced appetite, and weight loss. Larvae can burrow into synovial structures like tendon sheaths and joints.
NWS was eradicated from the United States in the 1960s but reemerged and has been reported in various animals since June 2026. If New World screwworm is suspected, veterinarians must be contacted immediately, and cases must be reported to state animal health officials and the USDA. Prompt examination and treatment are necessary for affected horses to prevent the continuation of the parasite’s life cycle.