By Dave Boxler and Matt Hille et.al
The New World Screwworm (NWS), Cochliomyia hominivorax, is among the most destructive livestock pests ever encountered in the Western Hemisphere.
Unlike most fly species whose larvae develop in decaying organic matter, New World Screwworm larvae feed exclusively on live tissue of warm-blooded animals.
This feeding behavior causes severe localized tissue destruction, promotes secondary bacterial infections, reduced productivity, animal welfare concerns, and frequently death if infestations are not detected and treated promptly.
Re-emergence and Northward Expansion
The current outbreak began in 2023 when Panama and Costa Rica reported increasing numbers of Screwworm cases north of the traditional containment zone at the border of Panama and Columbia. Since then, the pest has expanded throughout Central America and into Mexico.
By June 2026, more than 171,700 animal cases and over 2,000 human cases had been reported across Mexico and Central America. Infestations have been documented in livestock, companion animals, wildlife, and humans.
Detection of New World Screwworm in Texas
A major development occurred on June 3, 2026, when USDA-APHIS confirmed New World Screwworm in a three-week-old calf in Zavala County, Texas. The infestation was identified in the calf's umbilical region. This represented the first confirmed case in the United States in decades and demonstrated that the pest had successfully crossed the international border.
Source : unl.edu