New World Screwworm Returns to North America: Implications for Nebraska Livestock Producers

Jun 12, 2026

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

Video: How Data Predicts Swine Outbreaks - Swaminathan Jayaraman

In this episode of The Swine it Podcast Show Canada, Swaminathan Jayaraman, Research Assistant and PhD Candidate at Iowa State University College of Veterinary Medicine, explains how integrated data systems can improve disease surveillance in swine production. He discusses combining diagnostics, animal movement data, production records, and spatial analytics to identify risks earlier and support proactive decision-making for PRRS, PED, and swine influenza. Listen now on all major platforms!

"Disease surveillance remains largely reactive because outbreaks are often confirmed only after transmission has already occurred across multiple connected production sites."

Meet the guest: Swaminathan Jayaraman / swamjay is a Graduate Research Assistant at Iowa State University College of Veterinary Medicine. With academic training in management information systems and engineering, he focuses on integrating diagnostic, production, and movement data to improve disease surveillance and decision support in swine production systems. Listen to Swaminathan Jayaraman on The Swine it Podcast Show Canada, available on all major platforms.