Two more Texas screwworm infections found in animals far apart, USDA says

Dr. Isaac Bogoch explains the spread of the flesh-eating screwworm.

KERVILLE, Texas — Two more cases of the New World screwworm have been confirmed in Texas, demonstrating the difficulty of stopping the spread of a pest that could potentially devastate the nation’s cattle industry, the U.S. Department of Agriculture announced Monday.

The screwworm is actually a fly, which produces a larvae that eats live flesh instead of dead material. Females lay their eggs in open wounds of any warm-blooded animal such as cattle, but wildlife, pets and occasionally even humans can be infested.

The USDA said the new cases were found in a calf and a dog, hundreds of miles apart in La Salle and Andrews counties. That brings the total number of confirmed cases to four. The screwworm was first discovered in a three-week-old calf last week, and a second case was found only miles away in a young calf.

“While we address these instances that require immediate attention, and continue to sample suspected cases, we are simultaneously working to eradicate the pest entirely,” Dudley Hoskins, the USDA’s marketing and regulatory undersecretary, said in a statement.

Before it was eliminated in the U.S. in the 1960s, the fly was an annual warm-weather scourge of cattle ranchers.

The USDA and the U.S. cattle industry have been racing to prevent an infestation since the pest was detected in Mexico late in 2024 after decades of being contained at the southern end of Panama.

The government fights the fly by breeding sterile male flies, which then mate with wild females that only mate once in their monthslong life. By mating with sterile flies, the females don’t produce more flies and outbreaks can eventually be halted.

The USDA has announced plans to increase sterile fly production in plants outside the U.S. while it builds a fly factory in Texas.

USDA Secretary Brooke Rollins will be briefed on the infestation Monday afternoon at the U.S. Livestock Insects Research Laboratory in Kerville, Texas.