The New World screwworm, eradicated from the US in 1966, has re-emerged in Texas, with the first confirmed case on June 3, 2026, in a 3-week-old calf near La Pryor. Since then, cases have also been detected in southeastern New Mexico in a dog, and goats in Edwards and Gillespie County, Texas, totaling twelve active cases as of June 12. This re-emergence follows the parasite's northward movement through Central America, surpassing containment points that had held for decades.
The USDA and Texas Animal Health Commission (TAHC) have implemented measures such as quarantines, increased surveillance, and movement restrictions for animals within a 12-mile radius of infestations. The screwworm's spread is primarily attributed to animal movement rather than long-distance fly travel. In preparation, the USDA has released 131 million sterile male screwworms into Texas since early 2026, a part of the sterile insect technique (SIT) that was instrumental in the parasite's original eradication.
The cost of the initial screwworm infestation in the 1950s was estimated at $200 million annually, equivalent to over $2 billion today. To combat the current threat, the USDA has converted a fruit-fly plant in southern Mexico into a screwworm breeding facility for $21 million and is building a $750 million production factory at Moore Air Base in Edinburg, Texas. This new facility aims to produce 100 million sterile flies per week by late 2027, with a long-term goal of 300 million flies weekly. However, concerns exist regarding the time required to reach these production targets, as the parasite's numbers can rebound quickly in warm weather, and the current summer season has just begun.
The sterile insect technique (SIT), developed by Edward Knipling, involves releasing large numbers of sterile male flies into affected areas. These males mate with wild females, producing no offspring, thus reducing the population. This method successfully eradicated the screwworm from the US in 1966 and contained it in the Darién Gap between Panama and Colombia until 2022, when it breached this biological barrier. The exact mechanism of this breach and its entry into the US remains unknown, despite the US having charted the advancement of the fly through Central America since its arrival in Mexico in November 2024.
While officials like Dr. Phillip Kaufman of Texas A&M express confidence in winning this battle, the scale of the current infestation, spanning thousands of square miles across Texas, Mexico, and Central America, is far greater than the narrower frontier the original SIT strategy was designed to defend. The current challenge may necessitate exploring new tools, such as gene-drive insects, but the US currently lacks an established rapid pathway for authorizing their release, with jurisdiction split among agencies that have not yet approved such technologies.
