New World Screwworm Reappears in U.S., Prompting Expanded Surveillance Efforts

Federal agricultural scientists have confirmed a series of fresh New World screwworm infestations across several states, reviving concerns about the parasite’s capacity to spread among livestock and wildlife in the United States.

The New World screwworm (Cochliomyia hominivorax) is a flesh‑eating fly whose larvae feed on living tissue, causing painful wounds that can lead to severe infection or death if untreated. The insect primarily targets cattle, sheep, goats and, on occasion, wildlife, creating significant economic losses for producers.

Although an aggressive eradication campaign in the 1960s and 1970s eliminated the pest from the continental U.S., isolated reappearances have been recorded in recent years, underscoring the fragility of that success. The current cluster of cases signals a possible breach in the surveillance net that has protected the nation for decades.

Researchers with the U.S. Department of Agriculture’s Agricultural Research Service are now deploying a suite of tracking tools to map the flies’ movement. By analyzing the genetic signatures of captured specimens and overlaying those data on geographic information system (GIS) models, scientists hope to pinpoint the routes the insects are taking and identify hotspots where future infestations are most likely.

Veterinary officials stress that early detection is vital. Prompt treatment of affected animals can prevent the spread to nearby herds, and heightened awareness among ranchers can lead to quicker reporting of suspicious wounds.

The USDA is coordinating with state agriculture departments to expand trap networks and to consider reinstating the sterile‑insect technique—a method that once wiped out the pest by releasing millions of sterile males to disrupt breeding.

Continued monitoring and rapid response will be essential to keep the screwworm from re‑establishing a foothold, safeguarding both animal health and the agricultural economy.