USDA Announces New World Screwworm Detected in Texas Calf

In a press release dated June 3, 2026, USDA Animal and Plant Health Inspection Service  confirmed the detection of New World screwworm (NWS) in a 3-week old calf in Zavala County, Texas. NWS larvae were identified in the calf’s umbilical area. NWS was eradicated from the US in the 1960s other than a localized outbreak in Key deer in Florida in 2016-2017. NWS does not pose a risk to food safety and USDA’s Food Safety and Inspection Service ensures the nation’s food supply is safe. After re-emergence of NWS in Mexico in November 2024, the Swine Health Information Center has closely monitored NWS spread, hosted a webinar on the pest, and developed a new fact sheet for swine producers and other industry stakeholders.

NWS is a parasitic fly whose larvae feeds on the living tissue of warm-blooded animals including livestock, pets, wildlife, and in rare cases, people. Larval infestations (myiasis) can occur in any broken or damaged skin and cause rapidly progressing, painful wounds that can lead to serious injury or death if left untreated. 

The USDA APHIS release also said, “USDA and Texas officials are taking immediate action to contain and eradicate NWS from the United States, following the strategies and actions outlined in the NWS Response Playbook.” In response to the detection, authorities have established a unified incident command structure and implemented a comprehensive containment strategy, including quarantines, movement controls, enhanced surveillance, increased sterile fly release, expanded trapping efforts, wildlife monitoring, and targeted local outreach. These measures are designed to contain NWS infestation, prevent its spread, and accelerate eradication efforts.

NWS re-emerged in Mexico in November 2024. USDA increased monitoring, prevention, and mitigation practices to address this emerging disease threat to domestic livestock. Those efforts include ongoing aerial dispersion of sterile NWS flies in Mexico and along the Texas border to curb fly population growth as well as active surveillance for NWS flies in border states.

Read about NWS being discovered in Mexico in 2024 here.

Visit the Mexican government NWS dashboard here for the latest reporting data.

Swine producers can prepare for NWS by understanding the fly’s behavior and life cycle, identifying production and housing conditions that increase the risk of myiasis, implementing effective biosecurity, environmental, and wound management practices, knowing the response procedures for suspected infestations, and developing an NWS disaster management plan. Monitoring for clinical signs of NWS in swine remains critical, including nonhealing wounds, wounds with foul odor, biting or licking at wounds, depressed behavior, inappetence, and visible larvae in wounds. Any suspect cases of NWS should be reported immediately to state and/or federal animal health officials.

For more information, NWS resources are available here:

• ▪️SHIC NWS Fact Sheet 
• ▪️USDA Screwworm.gov 
• ▪️USDA APHIS website on New World Screwworm 
• ▪️TAHC NWS Fact Sheet 
• ▪️Panama-United States Commission for the Eradication and Prevention of Screwworm (COPEG) 
• ▪️Mexico’s Secretariat of Agriculture and Rural Development/National Service for Agri-Food Health, Safety, and Quality NWS Dashboard 
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The Swine Health Information Center, launched in 2015 with Pork Checkoff funding, protects and enhances the health of the US swine herd by minimizing the impact of emerging disease threats through preparedness, coordinated communications, global disease monitoring, analysis of swine health data, and targeted research investments. As a conduit of information and research, SHIC encourages sharing of its publications and research. Forward, reprint, and quote SHIC material freely. For more information, visit http://www.swinehealth.org or contact Dr. Megan Niederwerder at [email protected] or Dr. Lisa Becton at [email protected].