New World Screwworm by definition
New World Screwworm is a parasitic fly whose larvae feed exclusively on the living tissue of warm-blooded animals. A wound, a cut, an umbilical cord on a newborn calf — any opening is a potential site for a female fly to lay her eggs.
But unlike common fly maggots, once an animal is slaughtered, the parasite cannot survive — which means the risk to consumers is at the farm level, not the processing level.
“You're not going to get it from meat, and you're not going to see it in a steak or in ground beef.” — Dr. Mindy Brashears
USDA's Food Safety and Inspection Service (FSIS) inspectors examine live animals as they enter processing facilities and are trained to identify screwworm infestations. Mindy reports that FSIS has collected and sent samples to the Animal and Plant Health Inspection Service for identification — and none have recently come back confirmed as New World Screwworm.
How it disappeared and why it’s returning
The United States eradicated New World Screwworm in 1966 through the sterile insect technique, and over the following decades pushed the pest progressively south until it was contained below Panama's Darién Gap. The COPEG facility in Pacora, Panama became the operational backbone of that effort, producing and releasing sterile flies to maintain the barrier for decades.
“We don't know exactly why it came back. Most data points to it being carried back into Panama through the movement of both wildlife and potentially livestock being moved from South America back into Central America.” — Dr. Mindy Brashears
The barrier held until 2023, when detections in Panama spiked dramatically. From there it moved north through Central America, crossing into southern Mexico in late 2024. USDA closed the southern border to live cattle imports and surged resources into Mexico through Secretary Brooke Rollins' five-pronged response plan, pushing the expected US arrival back by nearly a full year.
The first confirmed US case was recorded on June 3, 2026, in Texas.
Current case numbers and what they mean
As of the recording date, USDA had confirmed 32 cases across Texas and New Mexico — 18 active, 13 resolved — with most concentrated in South Texas. The affected animals included 17 cattle, 10 sheep, 3 goats, and 2 dogs. The pest is highly treatable, and the first US case, a newborn calf infected at the umbilical cord, has since recovered fully.
“This is very, very treatable. Most of these have recovered.” — Dr. Mindy Brashears
Of more than 60,000 flies caught and analyzed across 8,000 traps, zero wild New World Screwworm flies have been found. Over 20,000 wildlife evaluations at the border have returned zero positives. Around 90% of suspect cases reported by producers are coming back negative, and Mindy says the numbers appear to reflect the real situation relatively accurately — unlike foodborne illness surveillance, where reported cases typically represent only a fraction of actual ones.
One Health, food security, and why this story belongs on a food safety podcast
The US cattle herd is already at historically low numbers, pressured by drought and prior trade disruptions. An unchecked screwworm outbreak would compound that directly — fewer animals means reduced meat availability and higher prices at the grocery store.
“Food security is national security.” — Dr. Mindy Brashears
Frank frames the screwworm story as a textbook example of One Health — the principle that animal health, human health, and food security are too interconnected to manage in separate lanes. Mindy agrees. A parasitic fly that never enters a processing facility and poses no direct risk to consumers can still drive up the price of beef, reduce supply, and expose vulnerabilities in a livestock industry already operating under stress. The food supply begins on the farm, and the screwworm outbreak is a reminder that threats starting there are food safety's business, too.
This episode of Smarter Food Safety is available now, wherever you get your podcasts. To learn more about the host, Frank Yiannas, and why Ecolab is partnering on this show, read our profile here.
Episode Field Notes
Terms and resources worth bookmarking for food and beverage operators this year.
USDA APHIS: New World Screwworm: The primary USDA hub for the outbreak response — surveillance data, sterile fly dispersal figures, and facility updates.
USDA's five-pronged screwworm response plan: Secretary Brooke Rollins' June 2025 announcement of USDA's strategy — sterile fly production, border surveillance, treatment stockpiling, domestic facility construction, and stakeholder coordination.
One Health — USDA overview: The integrated animal-human-environment health framework Mindy and Frank invoke throughout this episode as the lens food safety professionals need to apply to threats that originate outside a processing facility.
USDA cattle inventory report: The January 2026 USDA report showing the US cattle herd at its lowest level since 1951 — the supply context Mindy and Frank point to when explaining why a screwworm outbreak poses a food security risk beyond the immediate animal health threat.
