A parasitic fly that nearly vanished from American agriculture decades ago has returned with striking speed, triggering emergency containment efforts across multiple states and prompting warnings that delay could be costly.
Twelve confirmed animal infections have emerged since a single case was detected in a south Texas calf on June 3. Eleven cases remain active. The affected animals include cattle, goats, sheep, and one dog spread across six Texas counties and one New Mexico county, with the most recent infection discovered June 12 in a sheep in Sutton County.
The screwworm larva burrows into open wounds on livestock and warm-blooded animals, feeding on living tissue. The parasite had been virtually absent from the United States since the 1970s, when aggressive eradication efforts essentially eliminated it. Its sudden reappearance has alarmed agricultural officials who see the timing as particularly dangerous given current record-high beef prices.
Texas Agriculture Commissioner Sid Miller issued blunt language about the risk. "This should set off alarm bells across the country. Every day we delay gives this pest another opportunity to spread," he said in a statement last week.
The USDA's animal and plant health inspection service is asking livestock owners to watch for drainage or enlarging wounds, visible maggots or egg masses, unusual animal distress, and lesions around sensitive areas including the nose, ears, genitals, and umbilical region. Any suspected case should be reported immediately.
Federal officials have already mobilized a two-pronged response. Agriculture Secretary Brooke Rollins announced the release of 4 million sterile flies on the ground and 4 million more dispersed through the air to suppress the wild population.
Miller has also called for deployment of the Screwworm Adult Suppression System, or Swass, a USDA program that uses targeted bait to eliminate fertile adult flies before reproduction. "You don't win this battle with one tool," Miller said, outlining a strategy that combines sterile fly releases with targeted killing of reproductive adults, the same biological approach that created the protective barrier that kept the parasite out for nearly 60 years.
Pennsylvania has moved ahead with precautionary measures despite no cases in the state. The agriculture department issued a quarantine order requiring stricter controls on livestock imports from affected areas, including veterinary inspections and health documentation. Secretary Russell Redding framed the action as proactive biosecurity protection. "Taking proactive steps now to strengthen biosecurity and limit unnecessary animal movements from affected areas will help protect our farms and communities," he said.
Officials have made clear that despite the outbreak's severity for livestock producers, the US food supply faces no direct threat. The screwworm does not infest meat, fruits, vegetables, or other food products. The danger is entirely to animal health and farm economics.
Author James Rodriguez: "The speed of this resurgence should worry anyone paying attention to agricultural biosecurity, and the fact that Texas is calling for weapons that worked in the seventies suggests conventional tools may not be enough for whatever conditions are allowing this pest to gain ground now."
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