Why It Matters

USDA confirmed the first U.S. detection associated with the current New World screwworm (NWS) outbreak on June 3 in a calf in Zavala County, Texas. The agency has since confirmed additional U.S. detections, expanding concerns about livestock losses, wildlife surveillance, sterile fly production, and federal coordination.

The stakes are substantial for the Trump administration and Congress. A recent Congressional Research Service report highlights questions about coordination between USDA and the Department of the Interior on NWS surveillance and eradication in wildlife. H.R. 7466, the SAFE CATTLE Act, would require the two departments to enter into a memorandum of understanding to coordinate prevention, control, and eradication efforts involving wildlife and livestock.

USDA estimates that an outbreak comparable to the 1976 Texas outbreak could cost Texas livestock producers about $732 million annually and produce roughly $1.8 billion in losses to the broader state economy. With livestock and wildlife industries valued at over $11 billion in Texas, the economic pressure is significant. The administration also faces competing pressure over livestock trade: some ranchers and other industry stakeholders have pushed for reopening southern ports of entry, while others have urged USDA not to reopen prematurely. CRS notes that USDA announced a phased reopening strategy in July, subject to continued surveillance and the ability to suspend imports if risks increase.

The Big Picture

NWS spread beyond the biological barrier in Panama beginning in January 2023, later advancing through Central America and reaching southern Mexico in November 2024. The only fully operational sterile fly production facility in North America, located in Pacora, Panama, produces approximately 100 million sterile flies per week to support regional eradication efforts.

Neither USDA nor international authorities have publicly identified a single cause for the Panama barrier's breakdown. USDA has cited possible contributing factors including a 108% increase in the cattle population in the Darién region between 2006 and 2022, insufficient producer education about livestock wound care, and reduced supply and quality of some inputs used in sterile fly production. Researchers have also suggested that reduced genetic diversity or mating competitiveness in the long-established sterile fly strain may have contributed.

The containment strategy reflects decades of policy. Rather than attempting global eradication, the United States and regional partners established a permanent biological barrier in the Darién Gap to keep NWS from moving north from South America. Maintaining that barrier requires continuous production and release of sterile flies because wild NWS populations remain established farther south.

The outbreak has now reached the United States. As of Aug. 10, USDA had confirmed 45 U.S. detections, including 44 in Texas and one in New Mexico, according to CRS. Mexican authorities have reported more than 20,000 NWS cases since late 2024, including more than 1,200 active cases this year. USDA has responded with expanded surveillance, sterile fly releases, quarantines, animal movement controls, and eradication activities.

Congress has begun examining the response. Senate Agriculture Committee Chair John Boozman (R-AR) included NWS-related language in the Agricultural Act discussion draft released June 23, including a proposal tied to USDA's request to expand authority for financing sterile fly production and release. Lawmakers have also raised questions about USDA's response during congressional oversight of the department.

The Bottom Line

Researchers are exploring male-only strains, CRISPR-based gene editing, and gene drive systems that could supplement conventional sterile insect techniques. CRS says no single federal agency has primary responsibility for regulating gene drive organisms; oversight could involve USDA, the Food and Drug Administration, and the Environmental Protection Agency depending on the technology and its intended use.

The Defense Advanced Research Projects Agency also supports research involving emerging genetic pest-control technologies relevant to NWS. Wildlife presents an additional challenge because wild animals are more difficult to monitor, inspect, and treat than livestock and could complicate eradication if reservoirs become established.

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