U.S. Confirms First Case of New World Screwworm Since 1960s Eradication
A parasitic fly that can be fatal to livestock has been detected in a calf in southern Texas, marking the first confirmed case of New World screwworm in the United States in over 60 years.
The Discovery
The U.S. Department of Agriculture (USDA) confirmed the case on Wednesday after testing at the National Veterinary Services Laboratories in Ames, Iowa. The infestation was found in a three-week-old calf in La Pryor, Zavala County, Texas.
No other detections have been reported so far.
Understanding the Threat
The New World screwworm is the larval stage of a parasitic fly that infects warm-blooded mammals. The fly lays eggs in open wounds; once hatched, the larvae feed on the animal's living flesh, which can cause severe wounds or death.
Despite the alarm, USDA Secretary Brooke Rollins stated that the screwworm should not affect the food supply chain, as it does not infest meat, fruits, or vegetables.
The Long Road Back
Screwworm was successfully eradicated from the U.S. in the 1960s, but it has since re-emerged in Panama, Costa Rica, Nicaragua, and Honduras. Mexico reported its first case in 2024.
Since early 2025, the U.S. has deployed over 8,000 traps, testing 58,000 samples and 19,000 wildlife animals—all of which returned negative results until this case.
Containment Efforts
- In May 2025, the USDA restricted live animal imports from Mexico to prevent further spread.
- Primary control efforts rely on the sterile insect technique, a method of releasing sterile male flies to suppress reproduction.
- A new sterile fly production facility in Edinburg, Texas, is expected to open in fall 2027.
Political Reactions
The confirmation has sparked sharp criticism from state officials.
Rollins attributed the spread to "open-border policies of the last administration and the resulting illicit cattle movement."
Texas Agriculture Commissioner Sid Miller called the federal response "slow, bureaucratic, and incomplete," and formally requested approval to use the Screwworm Adult Suppression System (SWASS) .
State Rep. Don McLaughlin had previously claimed the screwworm was within a mile of the border—a statement Rollins initially dismissed but later acknowledged following the confirmed case.
Previous Incident
In February 2025, Florida officials detected screwworm larvae in an imported horse from Argentina during routine quarantine. Officials confirmed the infestation did not spread beyond the quarantine facility.