The USDA confirmed the first New World screwworm case in a U.S. cow in about 60 years, detected in a three-week-old calf in Zavala County, Texas. Officials are responding with quarantines, perimeter controls, and releases of sterile flies—after the pest’s earl
When a three-week-old calf in Zavala County, Texas, was found to have New World screwworm in its umbilical area, the news landed with a rare kind of urgency: not because it was unexpected to scientists, but because it meant a long-quiet threat had slipped back across the U.S. border.
The U.S. Department of Agriculture confirmed yesterday that this is the first case of the New World screwworm in a U.S. cow in about 60 years. The finding also marks the first instance of the agricultural pest in cattle since the screwworm was eliminated in the U.S. in 1966.
New World screwworms are parasitic flies that lay their eggs in open wounds or cuts, or in the eyes, ears, mouth, nose, or genitals of warm-blooded animals—including humans. The maggots hatch and burrow through the skin, producing painful, foul-smelling wounds.
For decades, livestock in the southern U.S. and Mexico suffered devastating screwworm outbreaks in the first half of the 20th century. Those outbreaks eventually ended there after an effort called the sterile insect technique helped collapse the fly population—sterile flies were released in Panama. and the change spread through the region.
But the screwworm never disappeared everywhere. It remained endemic to the Caribbean and South America. In 2005, it was estimated to cause annual economic losses of around $6.1 billion in today’s dollars. And in recent years. experts had been warning it was only a matter of time before the fly moved north through Central America and reached the U.S.
USDA officials say the agency is taking immediate action. Dudley Hoskins. the undersecretary for marketing and regulatory programs. said in a statement. “Protecting our livestock industry is a national security issue of the utmost importance. and USDA is wasting no time in taking action.” He added. “The United States has defeated this pest before. and we will do it again.”.
According to the USDA, the response includes forming an incident command team with the Texas Animal Health Commission. Officials are also establishing a 20-kilometer perimeter around the infection site, with quarantines and movement controls. The plan calls for releasing sterile New World screwworm flies from both the ground and the air. Authorities are trapping flies along the border, screening wildlife in the area, and doing outreach in local communities.
Residents near the Zavala County site are being asked to check pets and livestock for signs of infection. The USDA lists warning signs that include draining or growing wounds and screwworm maggots and eggs in or around body openings. If people suspect an infection, they should contact their state animal health official or a local USDA veterinarian.
Although New World screwworms rarely infect humans. they can infect people who live in or travel to areas where the flies are endemic. People who spend a lot of time outside and have open wounds are most at risk. Anyone who suspects they may have an infection should seek immediate medical care. The U.S. Centers for Disease Control and Prevention says people should not try to remove maggots themselves; a health care provider may need to remove them surgically.
The CDC also offers prevention guidance: keeping wounds clean and covered, sleeping indoors with closed windows or screens, and using insect repellant or wearing long-sleeved clothing.
The immediate focus now is stopping the insect before it becomes routine again—because for livestock producers. the screwworm doesn’t just mean discomfort. It means wounds that can turn deadly, and an outbreak that can ripple quickly through farms and supply chains. In Zavala County. officials are moving fast. using the same kind of science that helped eliminate the pest in 1966—sterile flies. strict containment. and relentless monitoring—while the rest of the U.S. waits to see whether this case is contained in time.
New World screwworm USDA Texas Zavala County sterile insect technique sterile flies quarantine livestock health parasitic flies CDC