US confirms New World screwworm in Texas

The USDA’s APHIS has confirmed the New World screwworm has returned to the United States, detected in a 3-week-old calf in Zavala County, Texas. Officials have established a 20 km infested zone with quarantines, movement controls, and surveillance, while a lon

When the USDA’s Animal and Plant Health Inspection Service confirmed the New World screwworm has been detected again within the United States, it landed with a thud in Texas—where ranchers and the wider cattle industry have been bracing for this moment.

This week, APHIS confirmed the parasitic fly known as the New World screwworm (NWS) is back inside America’s borders. For a pest eliminated from the United States in the mid-20th century. that single detection is more than a headline. It’s a reminder that time and geography can work against biosecurity.

The New World screwworm gets its “screwworm” name from how its larvae behave. The female fly lays eggs—typically in bodily openings like mouths, eyes, or genitalia, or in wounds. Once the eggs hatch. larvae. or maggots. emerge and use their screw-like shape to burrow deeper into an animal’s flesh. Unlike many maggots that feed on dead tissue, NWS larvae can eat living flesh too.

That’s why the consequences can be severe: the infestation can create wounds that become infected, making animals sick or even causing death. Large infestations have the potential to decimate cattle populations, and that, in turn, can ripple into beef markets already under strain.

The USDA’s confirmation points to a specific, local beginning—but it also carries a clear fear. If the screwworm spreads, beef prices—already sky high—could rise further, hitting ranchers and consumers alike.

The first detected case is in Zavala County, Texas. The county has a population of around 9,200 and sits about 31 miles east of the Texas-Mexico border. According to the USDA, the screwworm has been detected in a single bovine so far: a 3-week-old calf.

The larvae were discovered in the calf’s umbilical area. one of the natural openings the New World screwworm can infest. The fact that the known incident is limited to one calf is the only immediate relief embedded in the announcement. But the broader concern remains: given how large NWS populations can be. it’s likely this won’t be the only incident if the spread has already begun.

Even so. the detection marks a major defeat against the pest—because the New World screwworm was eliminated from the United States in the mid-20th century and. for decades. was mainly limited to Central and South America. In recent years, however, the pest’s movement has shifted. New World screwworm populations have been migrating northwards through Mexico. and as of last week. they are back in the United States.

The human risk is real, even if the most alarming version of it is unlikely.

The New World screwworm can infect nearly any kind of warm-blooded animal, including humans. Last year, an infestation was detected in a person in Maryland. That case involved a person who had traveled from Central America to the United States and is believed to have been infected while outside America’s borders. In other words, the screwworm had been found within the U.S. last year, but it appears to have been introduced through infected flesh carried into the country.

What’s different now is that the confirmed detection involves the pest crossing into the United States again and being present within the country’s environment—an outcome that changes the stakes for public health planning and local animal management.

To fight the current outbreak. the USDA says Texas officials have established “a 20 km infested zone” around the location where the infected calf was located. Inside that zone. the USDA has implemented “quarantines. movement controls. and surveillance.” The approach is designed to slow any spread by restricting movement and tightening monitoring.

But quarantines can’t stop something that flies.

That’s why the most long-term preventative measure being described is more aggressive: the release of millions of New World screwworms into the environment. The flies would be genetically modified to be sterile. Since a New World screwworm generally only mates once in its life. eggs laid after mating with a sterile partner would be unable to hatch. gradually suppressing the population by cutting off breeding over time.

The controlled release of sterile insects is a known method for managing similar threats. The USDA says 4 million sterile New World screwworms are already being released each week, and additional ones will now be released into the established zone.

For everyday Americans, the immediate danger may not be the screwworm itself. The bigger question is what happens next—whether further spread can be contained.

If containment fails. New World screwworm infections in humans could become a possibility. because the larvae can infect warm-blooded animals and can lead to life-threatening secondary bacterial infections. But the more likely impact for most people, should the infestation extend beyond the initial area, is economic.

Ranchers would face the first blow as cattle populations are threatened. Then the pressure would move outward into grocery aisles and fast-food lines. If cattle deaths rise. beef prices could follow upward. affecting how much it costs to buy a burger from McDonald’s or a steak from the supermarket. That kind of jump doesn’t land in a vacuum. Americans are already dealing with inflation and skyrocketing gas prices, and another squeeze on food spending would amplify daily strain.

New World screwworm USDA APHIS Zavala County Texas sterile screwworms cattle threat beef prices animal health human infection risk