Two New Screwworm Infestations Confirmed in Texas

Texas has confirmed two new, geographically separate cases of screwworm infestation, raising concerns about the pest's spread within the United States. The U.S. Department of Agriculture announced the findings, highlighting the challenges in controlling this parasite that could significantly impact the nation's livestock.

The screwworm, technically the larva of a specific fly species, feeds on the living flesh of warm-blooded animals. Female flies lay their eggs in the open wounds of livestock, wildlife, and even pets. While rare, humans can also become hosts.

The latest cases were identified in a calf and a dog, hundreds of miles apart, with no apparent contact between them. This brings the total number of confirmed screwworm cases in the U.S. to four. Previous cases involved a young calf last year and another nearby calf shortly after.

Officials are collecting samples from suspicious cases and working towards the complete eradication of the pest. The screwworm fly was previously eliminated from the U.S. in the 1960s but reappeared in neighboring Mexico in late 2024, decades after its eradication.

To combat the resurgence, the U.S. government is intensifying its production of sterile male flies. These sterile males are released into the wild to mate with native female screwworm flies. Since the females mate only once in their short lifespan, mating with sterile males prevents the production of new larvae, thereby suppressing the screwworm population. The USDA is expanding production facilities, including one planned for Texas, to bolster these eradication efforts.