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.
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