A resurgence of the New World Screwworm (NWS), a parasitic pest eradicated from North America in the 1960s, is generating alarm among U.S. livestock producers and lawmakers. A new wave of NWS outbreaks has emerged in Central America and is advancing north through Mexico towards the United States. NWS is a fly that reproduces by laying eggs on mucus membranes or in open wounds of warm-blooded animals, with hatched NWS larvae burrowing into flesh in a disease condition called “myiasis.” NWS myiasis can cause serious and often fatal damage to a variety of hosts, including cattle livestock, domestic pets, wildlife, occasionally birds, and in rare cases, as one unfortunate Maryland traveler has learned, people. NWS poses an immediate economic threat to the U.S. livestock industry and, as a result, the nation’s food supply and national security.

Key livestock industry stakeholders are closely monitoring the situation. Dr. Josh Szasz, head veterinarian at Five Rivers Cattle Feeding, has already developed contingencies for the nation’s largest cattle feeding operation. “We are poised to deal with the threat at our locations in the southern Plains and desert southwest,” he said. “This includes ongoing training of our animal health and stockpiling of more sophisticated parasiticides which have longer duration of activity against NWS. We have also allocated topical parasiticide for use in our cattle should we experience NWS.”

Regulators have been diligent in the initial NWS response, with eradication and surveillance strategies remaining the top priorities to combat the NWS advancement. In August 2025, the U.S. Department of Agriculture published its five-prong strategy, and earlier this year federal funding was allocated to modernize infrastructure for the “sterile insect technique” of population control. The breeding and release of sterilized male screwworms led to the eradication of the pest from the United States in the 1960s, and Szasz applauded these efforts.

“Construction of the sterile male fly production facility in South Texas is paramount to preventing NWS arrival in the United States, so it was very reassuring to see the federal government allocating a large sum of money, $750 million, for this facility,” he said. “This was perhaps the most important component of the federal government’s five-pronged approach to combatting NWS.”

Along with efforts to beef up eradication, lawmakers have called for development of new technologies for NWS surveillance and mitigation. These include new systems of deployable fly attractant traps. “Surveillance efforts like deployment of traps to monitor fly activity are underway in eight Texas counties along the southern border,” Szasz said.

Old technologies may also see new uses. There are no U.S. Food and Drug Administration-approved drugs indicated for treating NWS myiasis, but various off-label use studies suggest existing drugs may be effective at preventing or treating NWS myiasis in cattle and dogs, including antiparasitics (in cattle) and insecticides (in dogs).

The legal ramifications of the NWS resurgence are already surfacing. Regulatory compliance is front and center, as ranchers and shippers face new reporting obligations, mandatory inspections, quarantines, and port restrictions. Supply chain importers and exporters are particularly vulnerable, with the Animal and Plant Health Inspection Service (APHIS) and U.S. Customs and Border Protection enforcing restrictions of cross-border shipments of livestock. Supply contract disputes are likely to result from regulatory interruptions. And down the road, potential livestock losses to NWS will bring liability concerns. Ranchers may seek coverage under insurance policies, with resulting disputes over exclusions for “parasite-related” losses.

For now, APHIS stresses that rapid eradication is still achievable. Yet the clock is ticking: if the screwworm reaches the United States, livestock producers and regulators alike will face not only a biological crisis but a legal one, reshaping the livestock trade and liability landscape for years to come.

By Associate Henry Adams and Partner Joseph Blum

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