The U.S. has closed its southern border again to livestock imports, saying a flesh-eating parasite has moved farther north in Mexico than previously reported.

Mexico’s president was critical Thursday, suggesting that the U.S. is exaggerating the threat to its beef industry from the parasite, the New World screwworm fly. The female flies lay eggs in wounds on warm-blooded animals, hatching larvae that are unusual among flies for feeding on live flesh and fluids instead of dead material.

American officials worry that if the fly reaches Texas, its flesh-eating maggots could cause large economic losses, something that happened decades ago. The U.S. largely eradicated the pest in the 1970s by breeding and releasing sterile male flies to breed with wild females, and the fly had been contained in Panama for years; it was discovered in southern Mexico late last year.

The U.S. closed its southern border in May to imports of live cattle, horses and bison but announced June 30 that it would allow three ports of entry to reopen this month and another two by Sept. 15. However, since then, an infestation from the fly has been reported 185 miles northeast of Mexico City, about 160 miles farther north than previously reported cases. That was about 370 miles from the Texas border.

In Mexico, President Claudia Sheinbaum said authorities there are following all established protocols to deal with the northernmost case. Mexican authorities said the country has 392 infected animals, down nearly 19% since June 24.

“From our point of view, they took a totally exaggerated decision to closing the border again,” Sheinbaum said. “Everything that scientifically should be done is being done.”

Three weeks ago, U.S. Department of Agriculture Secretary Brooke Rollins announced plans for spending nearly $30 million on new sites for breeding and dispersing sterile male flies. Once released, those males would mate with females, causing them to lay eggs that won’t hatch so that the fly population would die out.