A parasitic fly that devastated American livestock herds before its eradication in the 1970s has turned up in a calf near the Texas-Mexico border, marking the first confirmed case in the state in nearly six decades and triggering urgent warnings from agricultural officials.
The New World screwworm was detected in an animal located about 50 miles from Mexico, according to Agriculture Secretary Brooke Rollins. The discovery comes after months of escalating concerns about the parasite's rapid spread through Mexico, which prompted repeated alerts to livestock owners across the country.
Female screwworm flies lay eggs in open wounds on cattle and other warm-blooded animals. The larvae that hatch feed on blood and tissue, and untreated infections prove fatal. While the parasite poses minimal direct risk to humans, its ability to spread rapidly through dense livestock populations makes it a serious economic threat, particularly as beef prices hover at record levels.
The last time the screwworm established itself in the continental United States, it caused tens of millions of dollars in losses before scientists developed a novel control strategy. Rather than simply kill the flies, researchers bred millions of sterile males that mate with wild females, whose eggs never hatch. Successive releases over time collapsed the population.
Rollins sought to contain alarm about the Texas discovery, stating there is no reason to expect the parasite will take hold in the country and no threat of mass infestation. The Texas case remains the only confirmed detection so far. Officials also pointed to successful containment in previous incidents, including a 2016 outbreak in the Florida Keys that was eliminated without spreading to commercial cattle operations.
Texas Agriculture Commissioner Sid Miller, however, expressed sharper concern. He criticized USDA efforts, noting that despite the release of billions of sterile flies, the screwworm has advanced over 1,100 miles from southern Mexico toward Texas. Miller called for deployment of an older, more aggressive control method called the screwworm adult suppression system, which combines attractants, baited traps, and targeted insecticides to reduce wild populations before sterile flies finish the job.
The USDA has prepared for this scenario. In March, the agency announced construction of a new facility at Moore Air Base in Edinburg, Texas, to breed sterile flies in partnership with the Army Corps of Engineers and private contractor Mortenson Construction. The facility aims to ramp up production capacity quickly if needed.
One complication: the US dismantled most of its sterile fly breeding operations after the 1970s victory, maintaining only a single facility in Panama for decades. That decision left the country less prepared to respond rapidly to resurgence, critics argue. Miller urged the incoming Trump administration to act decisively before the situation deteriorates.
In Mexico, the economic burden of treating screwworm infections has forced some ranchers into dangerous improvisation, applying gasoline, lime, and other crude substances to wounds in attempts to kill the parasites themselves.
Author James Rodriguez: "The screwworm's return is a reminder that eradication is never truly permanent, and letting your guard down in border regions invites trouble."
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