When New World screwworm was first detected 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. Monitoring swine cases in Mexico is an important component to evaluating risk to the US swine herd. As of April 1, 2026, over 1,270 swine have been affected with NWS in Mexico, representing approximately 6.5% of total cases.
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 US in the 1960s, the increasing number of confirmed cases in Central America and Mexico starting in 2024 has 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.
In total, reports from Mexico as of April 5, 2026, indicate that 19,677 head of livestock have been affected with 1,290 active cases, 120 of which were swine. Other active cases include 726 bovine, 309 canine, 72 equine, 37 sheep, 3 humans, 12 goats, six feline, and one bird. Accumulated totals of affected species since November 2024 include 13,217 bovine, 3,220 canine, 1287 swine, 962 equine, 517 sheep, 196 humans, 149 goats, 86 feline, and 30 birds.
NWS has not been found in the US since the 2016 – 2017 localized outbreak in Key deer in Florida. The concentration of NWS cases is in south and central Mexico; however, cases have been reported as closely as Nuevo Leon, just 70 miles south of the US border. The continued expansion of NWS case detections in Mexico highlights the critical need for continued vigilance to detect and report suspect cases in the US. The Swine Health Information Center supports producer awareness for this emerging disease through sharing regular NWS updates, hosting a webinar on the pest, and developing a new fact sheet and other resources for swine producers and other industry stakeholders.
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.
On February 9, 2026, USDA announced the completion of a US-based NWS sterile fly dispersal facility in Edinburg, Texas. The announcement noted that the facility will expand USDA’s ability to disperse sterile flies along the border and into the US, if necessary. US Secretary of Agriculture Brooke Rollins stated, “This sterile fly dispersal facility was a high priority project, and our team delivered it in record time. This new facility is a monumental achievement for our domestic preparedness efforts, but we are also diligently working to stop the spread of screwworm in Mexico, conduct extensive trapping and surveillance along the border, increase US response capacity, and encourage innovative solutions. We will never stop fighting to protect American agriculture. USDA, through a whole-of-government approach, will continue to hold Mexico accountable to mitigating the spread of this dangerous pest.”
USDA has recently announced plans to start building a new sterile fly production facility in Edinburg, Texas later this year in addition to a $21 million investment to help renovate and convert an existing fruit fly facility in Metapa, Mexico. The Metapa, Mexico facility is expected to produce an additional 60 to 100 million sterile NWS flies per week. With continued support from USDA APHIS technical experts, Mexico expects production to begin there as early as summer 2026.
Providing publicly available, science-based information through fact sheets, monitoring reports, and stakeholder updates supports SHIC’s mission of minimizing the impact of emerging disease threats through coordinated communication of key resources and improving swine health information.
For more information, NWS resources are available 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].