An update on the New World screwworm outbreak
By Easton Martin | June 18, 2026
Agricultural authorities are escalating their containment efforts across the American Southwest following the first domestic detections of the New World screwworm in six decades.
The U.S. Department of Agriculture confirmed the first case on June 3, 2026, in a three-week-old calf on a ranch in Zavala County, Texas. Since that initial discovery, the flesh-eating parasitic pest has spread to at least twelve confirmed animal cases, primarily affecting cattle, sheep, goats, and a domestic dog. While eleven of the active cases are concentrated within several Texas counties, including Gillespie, La Salle, and Sutton, an isolated case was also detected in Lea County, New Mexico.
The New World screwworm is the larval stage of a reclusive fly that lays its eggs in the open wounds of warm-blooded animals. Once hatched, the maggots burrow into the living tissue, causing severe wounds and potentially fatal infections if left untreated. The parasite was effectively eradicated from the United States in 1966 through the large-scale release of sterile male flies, a biological control method that causes wild female flies to lay unhatched eggs.
The current outbreak stems from a broader resurgence that began in Panama and Costa Rica in 2023, moving steadily northward through Central America and Mexico over the past two years. Warm winter temperatures have facilitated the northward migration of the pest. In response to the domestic cases, the federal government has initiated a massive containment campaign, establishing 12-mile quarantine zones around every confirmed detection area.
Federal response teams have already deployed millions of sterile flies through both aerial and ground releases in the affected regions. Texas Agriculture Commissioner Sid Miller urged aggressive action, calling for the immediate deployment of the Screwworm Adult Suppression System, a targeted baiting program designed to kill fertile adult flies before they can reproduce.
