Screwworm reaches US cattle, raising threat to ranchers and trade
Why it matters: The parasite can devastate herds, and the response depends on sterile-fly releases and US-Mexico coordination.
The New World screwworm has been detected in U.S. cattle, escalating a long-running livestock threat into an immediate risk for ranchers and the food supply chain. The flesh-eating parasite, Cochliomyia hominivorax, spreads when its larvae infest living tissue in mammals, including cattle and, in rare cases, people. A key control method is releasing sterile flies to suppress wild populations over time. The article says the U.S. Department of Agriculture has been working with Mexico since April 26, 2025, to open airspace for those releases and strengthen cross-border containment. The outbreak also heightens pressure on livestock imports and broader animal-health defenses.