Two More Texas Screwworm Cases Confirmed, USDA Warns of Spread

The U.S. Department of Agriculture has confirmed two additional cases of New World screwworm (NWS) in Texas cattle, bringing the total to four confirmed infections as the flesh-eating parasite continues to spread far beyond the initial detection zone, according to AP News. The new cases — a calf in La Salle County and a dog in Andrews County — were found hundreds of miles apart, signaling a significant escalation in the containment challenge.

Background: A Pest Eradicated for Decades

The New World screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae feed on the living flesh of warm-blooded animals. Unlike most fly species that consume dead tissue, screwworm larvae burrow into open wounds, causing severe infections and often death if untreated. The pest was successfully eradicated from the United States in the 1960s and 1970s through an innovative sterile insect technique program, with the last confirmed case in Texas recorded in 1966, as The Guardian reported.

For decades, a single sterile fly breeding facility in Panama maintained a biological barrier at the Darién Gap. However, the parasite broke through that barrier in late 2024 and began advancing through Mexico, traveling over 1,100 miles toward the U.S. border.

The Current Outbreak

The first case was confirmed on June 3-4 in a three-week-old calf in La Pryor, Zavala County, about 50 miles from the Mexico border. Texas State Veterinarian Bud Dinges established a 12-mile (20-kilometer) quarantine zone around the detection site, prohibiting the movement of any warm-blooded animal without inspection. A second case was confirmed days later in another calf nearby.

Now, the two new cases in La Salle and Andrews counties — separated by hundreds of miles — demonstrate the difficulty of containment. The infected dog in Andrews County had recently been in Mexico, raising concerns about cross-border transmission through pets and wild animals, as Fortune reported.

Economic Stakes at Record Highs

The outbreak comes at a particularly vulnerable moment for the U.S. cattle industry. The national cattle herd is at its smallest in 75 years following years of drought, high feed costs, and industry consolidation. Beef prices are already near record levels — ground beef hit $6.89 per pound in May 2026. Canada has already restricted livestock imports from Texas, demonstrating the immediate economic consequences, according to El País.

While the screwworm does not infest meat or fruit — posing no direct food safety risk — an uncontrolled spread could devastate cattle populations, leading to shortages and further price increases.

Federal vs. State Disagreement on Response

A significant tension has emerged between the USDA and Texas state officials over the appropriate response. Agriculture Secretary Brooke Rollins has sought to reassure the public, stating there is “no threat of mass infestation” and that the USDA is confident in its preparations. The USDA has deployed 8,000 fly traps along the U.S.-Mexico border and tested more than 58,000 fly samples and 19,000 wild animals.

However, Texas Agriculture Commissioner Sid Miller has been sharply critical of the federal response. “For months, the screwworm has advanced rapidly through Mexico in spite of the USDA’s existing gameplan,” Miller said in a statement. He has urged the administration to deploy the SWASS poison bait system, which the USDA has resisted due to concerns about its impact on other insects and animals.

The Sterile Fly Strategy

The USDA is doubling down on the sterile insect technique that successfully eradicated screwworm in the 20th century. The agency is building a massive $750 million sterile fly factory at Moore Air Base in Edinburg, Texas, and converting a facility in Mexico that should be operational by July 2026. Female screwworm flies mate only once in their lifetimes, so eggs from sterile matings do not hatch, causing the population to die out over time.

What to Watch For

The coming weeks will be critical. The parasite prefers humid areas with temperatures above 77°F (25°C), making summer a high-risk period for potential spread. University of Florida entomologist Edward Burgess noted that increased vigilance may lead to more detections: “When that first case is seen, everyone is being vigilant and their eyes are on it more intensely. And when you are looking for something, you are more likely to see it.”

Key questions remain: How far has the screwworm actually spread beyond the four confirmed cases? Will other countries follow Canada’s lead in restricting Texas livestock imports? And can the quarantine zones hold given the geographic dispersion of cases? The answers will determine whether this outbreak remains containable — or becomes the first establishment of screwworm in the U.S. in six decades.