Screwworm Case Spurs New USDA Strategy to Bolster Livestock Safeguards

EDINBURG, Texas (AP) – Federal and state authorities are ramping up efforts to shield the U.S. livestock industry after the nation’s first human case of New World screwworm in decades, even though officials emphasize current risks remain minimal.

On August 4, the Centers for Disease Control and Prevention confirmed a traveler returning from El Salvador had contracted the parasitic fly, marking the first such case in the U.S. since 2017. A federal official said the incident is the only case reported in 2025 and does not pose a threat to agriculture. No infections have been detected in livestock, and targeted surveillance has yielded no further cases.

The USDA immediately activated its monitoring systems in a tight radius around the case location, deploying traps and testing to ensure early detection. All results have so far come back negative.

Simultaneously, Agriculture Secretary Brooke Rollins announced a sweeping response plan, unveiling a $750 million sterile fly production facility to be constructed at Moore Air Force Base near Edinburg. Once operational, the plant will produce up to 300 million sterile New World screwworms weekly. The U.S. currently relies on production facilities outside its borders, primarily in Panama, to supply sterile flies used for bio-control in containment zones.

Rollins said the facility is a long-term measure designed to triple sterilized fly output and reduce U.S. dependence on international sources. The approach revives a strategy first deployed in the 1960s and 1970s when coordinated releases of sterile male flies helped the U.S. eradicate screwworms, then endemic to the southern states.

In the years that followed, screwworms were declared eradicated in the continental U.S., with only sporadic traveler-linked human cases in more recent years. Human infection, while rare, can be painful and potentially serious. Female screwworm flies lay eggs in open wounds on warm-blooded animals; the larvae feed on living tissue, causing tissue damage and potentially fatal infections if untreated.

At present, health agencies stress that the public health risk remains low. In Maryland and nearby jurisdictions, officials have conducted contact investigations and warned health providers to watch for symptoms consistent with screwworm infestation.

Federal authorities are coordinating shipments of sterile flies from foreign facilities for immediate use, even as construction of the domestic facility proceeds. The Texas project is expected to reach partial operations in 2026.

Screwworm continues to circulate in parts of Central America and southern Mexico, and recent livestock outbreaks just across the border have elevated concern. Updated data shows a 53 percent increase in reported screwworm cases in Mexico between July and mid‑August, reinforcing the urgency of the U.S. response.

Meanwhile, farm and livestock groups in South Texas say they appreciate the increased biosecurity, but some expressed concern over how quickly information was shared after the Maryland case became public via national media rather than direct briefings.

Federal officials say communication protocols were activated appropriately, and with no immediate livestock threat, public alerts were handled by health rather than agriculture channels.

As the sterile fly facility nears construction, planners say it will complement broader USDA efforts to trap along the U.S.–Mexico border and reinforce the multi-layered strategy to keep screwworm at bay.

The investment in domestic screwworm suppression is being framed not as an emergency reaction, but as a calculated reinforcement of national biosecurity, a hedge against future vulnerabilities amid rising cross-border animal disease pressure.

According to the USDA’s Animal and Plant Health Inspection Service (APHIS), the United States remains officially free of New World screwworm in its animal population. The last major domestic outbreak occurred in 2016 on Big Pine Key, Florida, where more than 100 cases were confirmed in Key deer and domesticated animals. The outbreak was successfully contained through an emergency sterile fly release and aggressive surveillance campaign. That episode, and the current response, both point to the enduring relevance of sterile insect technique (SIT), developed more than half a century ago by U.S. entomologists.

The method’s strength lies in its non-chemical, species-specific approach. Male flies, sterilized through irradiation, are released in large numbers into the environment. When they mate with wild females, no offspring are produced. The population dwindles generation by generation.

This technique was instrumental in eliminating screwworms from the U.S. south and then pushing the active eradication zone steadily southward. Today, the Panama-Colombia border remains the final control barrier, with sterile flies released continuously to prevent northward migration.

But agricultural economists and federal planners have warned in recent years that the system’s durability depends on maintaining both international cooperation and infrastructure investment. The decision to build a production plant in Texas reflects lessons learned from pandemic-era disruptions and ongoing strain in global logistics chains.

Construction is expected to begin in early 2026, pending final environmental reviews and budget disbursements. When completed, the facility will serve both domestic and regional needs, including potential surge response in neighboring countries.

In addition to bolstering resilience, planners say the facility will create 350 full-time jobs and generate new collaboration opportunities with Texas A&M AgriLife Extension, which has a long history of livestock pest research.

Texas ranchers, who remember the Big Pine Key incident and previous regional threats, have expressed support for the expanded capacity, particularly given the rise in cross-border livestock traffic and warming climate conditions that may extend fly habitat ranges.

Historically, the screwworm’s footprint was bounded by frost lines. But with average temperatures rising, the risk map is shifting. Entomologists note that extended warm seasons and increased humidity can expand the window for fly activity, increasing the importance of year-round monitoring.

So far, no new livestock rules or movement restrictions have been issued. State agencies continue to advise ranchers and veterinarians to remain alert and report any unusual infections or slow-healing wounds in livestock. Quick reporting is a key part of the containment model: early detection ensures targeted, limited interventions rather than broad quarantines or emergency import controls.

At a time when U.S. agriculture is facing heightened scrutiny over foreign animal diseases, African swine fever, avian influenza, and now lumpy skin disease among them, the return of screwworm, even in a single human case, has prompted a renewed emphasis on readiness.

Analysts at the Congressional Research Service have noted that funding for surveillance and rapid response remains uneven across agencies. The USDA's decision to allocate nearly three-quarters of a billion dollars toward screwworm prevention marks one of the most significant single investments in non-viral livestock disease control in over a decade.

As the Texas facility moves forward, officials say it will operate in tandem with existing surveillance grids and genetic tracing tools used to confirm fly origin in future cases. In the Maryland instance, genetic markers confirmed the patient’s flies matched strains known to exist in Central America, helping rule out a domestic source.

No cases have emerged in animals, nor have any new human exposures been reported. The incident is now classified as resolved from a public health standpoint, though it remains under active review by agricultural authorities as a biosecurity prompt.