A steer stands in a pen with other livestock at the annual Buc Days Rodeo in American Bank Center in Corpus Christi, Texas, on May 9, 2025.
Veracruz, Mexico – In a development that sounds more like a horror film than agricultural policy, officials in Mexico have confirmed a new case of New World screwworm (NWS), a flesh-eating parasite known for burrowing into warm-blooded animals and devouring living tissue from the inside out. The detection, reported Wednesday by Mexico’s National Service of Agro-Alimentary Health, Safety, and Quality (SENASICA), has prompted an immediate shutdown of livestock trade across U.S. southern border ports.
The latest case was discovered in Ixhuatlán de Madero, Veracruz—just 370 miles from the U.S.-Mexico border and approximately 160 miles north of Mexico’s current sterile fly dispersal zone, the country’s frontline defense against the parasite’s spread. The location of the new detection signals a troubling expansion of the pest’s range, and it comes less than two months after earlier northern detections in Oaxaca and Veracruz triggered the initial closure of ports to cattle, bison, and horses on May 11.
Although U.S. officials had announced a phased reopening of five livestock ports beginning July 7, those plans have now been put on hold. In response to the new threat, U.S. Secretary of Agriculture Brooke L. Rollins ordered an immediate halt to all livestock trade through southern ports, citing the need to safeguard American herds and the nation’s food supply.
New World screwworm is not just a nuisance—it’s a deadly, fast-replicating parasite that can decimate herds. Once inside an animal’s body, the larvae feed on live tissue, creating festering wounds and often requiring euthanasia of the host. In humans, infection is rare but harrowing, with surgical removal of larvae the only option.
The USDA has responded with what Secretary Rollins described as a “Bold Plan” to push back against the growing threat. That includes construction of a sterile fly dispersal facility in South Texas and design plans for a domestic production site. The sterile fly program works by overwhelming wild populations with flies that cannot reproduce, gradually reducing the pest’s numbers. The USDA hopes to expand this strategy, long successful in Central America, to hold the line at the U.S. border.
Rollins emphasized that the United States would not reopen its ports until Mexico demonstrates significant containment progress in Veracruz and surrounding states. USDA personnel continue to conduct on-site inspections in Mexico to verify that surveillance and quarantine protocols are being implemented.
For now, the biological threat of NWS has triggered not only a regional agricultural emergency but a chilling reminder of how fast nature can break through borders. The parasite, once thought to be under control, is creeping closer to the U.S., and officials warn that the line between containment and catastrophe is increasingly thin.
With billions of dollars in agricultural production at stake, the fight against NWS has taken on a new urgency. Whether the containment efforts succeed—or whether this parasite breaks through into the American heartland—remains to be seen.
