The United States is responding to the reappearance of the New World screwworm, a flesh-eating parasitic fly that was recently detected in a calf in southern Texas.

The pest had been eradicated from the United States in 1966 and pushed as far south as Panama by 2006, but its spread northward from Mexico has now brought it back into the country.

Screwworm larvae infest open wounds and feed on living tissue in warm-blooded animals, posing a significant threat to livestock and occasionally infecting humans.To prevent a wider outbreak, the US Department of Agriculture (USDA) is relying on the sterile insect technique, a method developed in the 1950s.Male screwworm flies are sterilized through radiation and then released into affected areas.

Because female screwworm flies typically mate only once, mating with sterile males prevents reproduction and causes local populations to decline rapidly.

The USDA has established a containment zone around the infected calf and is conducting targeted releases of sterile flies while continuing larger aerial releases near the US-Mexico border.Officials estimate that approximately 400 million sterile flies per week are needed to suppress the pest effectively.Current production capacity is about 100 million flies per week at a facility in Panama.

To increase capacity, the USDA is investing in the renovation of a facility in Metapa, Mexico, expected to add 60 to 100 million sterile flies per week.

The agency is also accelerating plans for a new sterile-fly production facility in Texas, although it is not expected to become operational until late 2027.

Experts remain confident that the screwworm can be eradicated again, but they warn that additional cases may appear before control efforts fully take effect.