Cattle border reopens as screwworm fight struggles with sterile fly shortage

The United States has begun reopening its southern border to cattle from Mexico even as the flesh-eating parasite that triggered the closure more than a year ago remains uneradicated, with officials still short of the sterile flies needed to stop it.

The New World Screwworm, whose larvae feed on living tissue, has been moving northward through Central America and into Mexico, breaching a biological barrier that had held for decades after a 45-year eradication campaign pushed the pest out of the United States by 1982 and down to Panama by 2006.

The main weapon against the parasite is the sterile insect technique: hundreds of millions of sterilised male flies are released to mate with wild females, collapsing the population over time. But production capacity cannot currently supply the numbers required to halt the outbreak's advance.

The parasite's arrival in Texas would threaten one of the world's largest cattle industries, and stakeholders across the political divide agree the country is not producing enough sterile flies.

Agriculture authorities are racing to expand breeding facilities for sterile flies while deploying detector dogs and tightening inspection protocols at border crossings.

International agencies have also joined the effort, launching a regional project to support the sterile fly campaign across Central America, Mexico and the United States as governments warn the outbreak could take years to contain.