One of the most successful eradication programs in the history of American public health and agriculture achieved something remarkable: the complete elimination of the New World Screwworm fly (Cochliomyia hominivorax) from the United States in 1966. The screwworm — named for the screw-like motion its larvae use to burrow into the living flesh of warm-blooded animals — is considered one of the most economically and medically devastating livestock parasites in the Western Hemisphere. For decades, its absence from U.S. soil has protected American cattle, horses, wildlife, and, in rare cases, humans, from a condition that can be fatal if untreated.
That protection was breached in 2026. USDA Animal and Plant Health Inspection Service (APHIS) confirmed the detection of New World Screwworm in cattle in Maverick County, Texas — a county along the Rio Grande in southwest Texas that borders Mexico's Coahuila state. The detection followed confirmation of the parasite's re-emergence in livestock in Mexico in 2024 and 2025, where USDA and Mexican authorities have been engaged in emergency sterile insect technique (SIT) operations to prevent northward spread. USDA closed the US-Mexico border to cattle imports in November 2024 following the initial Mexican detections, citing the risk of screwworm importation — a decision that proved prescient.
