Plate Nº 16 · recorded October 10, 2026
Health & Medicine ResearchReported finding
Flesh-eating screwworm resurfaces in Texas and New Mexico
A parasitic fly whose larvae eat living tissue has returned to Texas and New Mexico. UC San Diego built a county-level risk dashboard; the USDA is reviving the sterile-fly strategy from the 1950s.
By Nathan Brooks4 min read898 words
In brief
- New World screwworm has confirmed detections in Texas and New Mexico as of September 2026, with the first northward-move warnings issued in 2023.
- The pest caused an estimated $50 million to $100 million in annual livestock damage in the U.S. Southwest in the 1950s before being eradicated.
- The 1950s eradication campaign used the sterile insect technique — sterilizing male flies with radiation and releasing them to collapse wild populations.
- The risk dashboard was built jointly by UC San Diego and the County of San Diego Health and Human Services Agency, with access initially limited to public health partners.
- Resilient Shield, the parent initiative, is one of 13 core facilities in the CDC's new Insight Net outbreak-modeling network.
New World screwworm — a parasitic fly whose larvae feed on living tissue — has reappeared in the United States, with confirmed detections in Texas and New Mexico, researchers at the University of California San Diego said on September 15, 2026.
In the 1950s, the pest caused an estimated $50 million to $100 million in damage to livestock in the U.S. Southwest each year before a sweeping eradication campaign eliminated it from the country and pushed its range south to Panama. Now, roughly seven decades later, it is moving north again.
The return has triggered an unusual partnership between a county public health agency, UC San Diego engineers and the U.S. Department of Agriculture. Their goal: predict where the fly might strike next and deploy the sterile-insect strategy that worked before.
What does the dashboard actually do?
The tool, built by UC San Diego and the County of San Diego Health and Human Services Agency, generates county-level risk profiles across the United States. It pulls together three streams of data:
- Confirmed screwworm detections
- Environmental conditions favorable to the fly and its larvae
- News media reports that may flag outbreaks before official systems catch up
For now, only public health officials and project partners can access it. The team plans a public version later.
One of the dashboard's most unusual features is its use of news coverage. Dr. Seema Shah, medical director of the Epidemiology and Immunization Services Branch for San Diego County, called that integration a deliberate choice.
"Traditional reporting mechanisms for public health are often delayed," she said. "Lab confirmation can take days or weeks. By incorporating media reports, we can identify potential threats sooner and stay one step ahead."
Why is screwworm so dangerous?
Most fly larvae consume dead or decomposing matter. New World screwworm larvae do the opposite: they burrow into healthy flesh.
Female flies lay eggs in open wounds or natural body openings. After hatching, the larvae feed on living tissue, enlarging wounds and raising the risk of secondary infections. Severe, untreated infestations can kill livestock and wildlife.
Human cases are rare, and the parasite does not spread from person to person the way COVID-19 does. Larvae can still enter wounds or mucous membranes, where they must be removed quickly to limit damage.
The pest can travel. Adult flies cover miles while searching for hosts, and infected livestock, pets, birds and wildlife can carry it into new territory.
How fast is it spreading?
Dr. Mark Beatty, assistant medical director for the county's Epidemiology and Immunization Services Branch, said the northward move was expected but not this rapid.
"We knew in 2023 that New World screwworm was going to move northward, but I wasn't expecting it to move as fast as it has," he said. "Although the source of the infections in the U.S. is still under investigation, the fact that it's in the U.S. is 100% clear."
"Once it entered Texas, we quickly saw an increase in detections," Beatty added. "It's in a place where it used to live, so it's not surprising it's taking a hold again."
Can the U.S. beat it again?
Officials are turning to the same weapon that worked in the 1950s: the sterile insect technique. Researchers raised huge numbers of male flies, sterilized them with radiation, and released them into the wild. When wild females mated with sterile males, they produced no viable offspring, and the population collapsed.
The USDA is now combining sterile-fly releases with pesticides and movement-limiting quarantines. The agency is also seeking U.S. Environmental Protection Agency approval for a genetically modified all-male strain currently in field trials. UC San Diego researchers, meanwhile, are developing next-generation genetic tools that could strengthen future eradication work.
Dr. Emily Trumbull, a veterinarian leading the county's One Health Program, said local surveillance is critical. Her team is working with the California Department of Food and Agriculture to connect local veterinarians with screwworm resources across livestock, pets and wildlife.
How does the broader network work?
The screwworm dashboard grew out of Resilient Shield, a UC San Diego initiative funded by the U.S. Centers for Disease Control and Prevention. Resilient Shield is one of 13 facilities in the CDC's new Insight Net, a national network built to model outbreaks and disease threats.
The model is simple. Public health agencies name their most urgent problems. Researchers then build tools around those priorities rather than the other way around. The first request Resilient Shield received came from Shah and involved tracking influenza; that project was co-led by co-PI Ruy Ribeiro at Los Alamos National Laboratory.
For the screwworm project, lead investigator Dr. Eliah Aronoff-Spencer partnered with mathematical epidemiologist Dr. Natasha Martin, both at UC San Diego School of Medicine. Technology partners include Google and MITRE. The shared infrastructure lets the team assemble new tools quickly when a fresh request arrives.
"Our central innovation is the true convergence of partner priorities with scalable engineering," Aronoff-Spencer said. "We do not build in a vacuum. Our infrastructure is built directly on the priorities dictated by our partners."
The Resilient Shield hub now pulls in data on human disease, livestock, weather, environmental conditions, national health records and social media. The same modular framework could tackle the next outbreak, whatever it turns out to be.
via sandiegocounty.gov (Original)
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