By Lindsay Westbrook & Anais Jayr
For nearly 60 years, New World screwworm was largely a problem of the past for the United States. That changed in 2026. In June, the U.S. Department of Agriculture confirmed New World screwworm in cattle in South Texas, the first confirmed U.S. livestock detection in decades.
The detection followed a northward expansion that began when New World screwworm moved beyond the biological barrier in Panama in 2023, spreading through Central America and reaching Mexico in 2024. Its continued movement north prompted restrictions on livestock entering the United States from Mexico and intensified surveillance along the border. By 2026, cases had been detected in Texas and New Mexico.
For the latest case counts and locations, visit USDA’s Detection Dashboard.
The California Department of Food and Agriculture (CDFA) reports no confirmed detections of New World screwworm in California. State officials are working with federal and neighboring state agencies to monitor the situation, including through fly trapping along California’s borders, and are implementing additional animal-entry requirements to help prevent its spread.
For livestock producers, the return of New World screwworm is a serious animal-health and economic concern. For consumers, however, it is important to understand what it is, and what it is not. New World screwworm is not a foodborne pathogen, and eating beef is not a route of transmission. Its potential effects on consumers are indirect, primarily through animal health, cattle movement, trade and livestock supply.
Source : ucdavis.edu