Following the news of New World screwworm being detected in Mexico in November 2024, USDA increased efforts to prevent the insect’s entry into the United States. Monitoring and mitigation practices were initiated, including the regular aerial introduction of sterile NWS insects in Mexico to curb population growth. The US swine industry considers NWS a potential emerging threat to swine health. Consequently, the Swine Health Information Center has shared regular NWS updates, held a webinar on the pest, and now makes a fact sheet available as a resource for swine producers and other industry stakeholders.
From the NWS fact sheet:
New World screwworm (NWS) is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals including livestock, pets, wildlife, and 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. Although NWS was eradicated from the United States in the 1960s, the increasing number of confirmed cases in Central America and Mexico starting in late 2024 have renewed concern about risks to swine health, human safety, and farm profitability.
In Texas alone, projections estimate that an NWS outbreak could result in more than $1.8 billion in livestock losses (USDA APHIS, 2025). Due to significant animal health and economic impacts, suspected cases of NWS must be reported to state animal health officials and the USDA immediately. For comprehensive information regarding NWS, visit screwworm.gov.
Swine producers can prepare for NWS by understanding the fly’s behavior and life cycle, identifying production and housing conditions that increase risk of myiasis, implementing effective biosecurity, environmental, and wound management practices, knowing the response procedures for suspected infestations, and developing a NWS disaster management plan.
From the USDA’s screwworm.gov website:
In Figure 1, taken from USDA’s screwworm.gov website on January 29, 2026, NWS detections in Mexico are tracked to date. NWS has been reported as close as 70 miles south of the US/Mexico border and reports include the first swine infestation in Mexico. The website also contains extensive information and resources on the US response to NWS.
Figure 2 illustrates NWS geographic occurrences in Mexico, including the Nuevo Leon sites near Texas, sourced from USDA’s screwworm.com website.
Additional resources for producers:
For more information, NWS resources are available from the USDA APHIS website on New World Screwworm, the TAHC NWS Fact Sheet, and the Panama-United States Commission for the Eradication and Prevention of Screwworm (COPEG).
Providing publicly available, science-based fact sheets supports SHIC’s mission of minimizing the impact of emerging disease threats through coordinated communication of key resources and improving swine health information. The SHIC NWS and other swine disease fact sheets can be found here.
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].