A medical mystery in Maryland has jolted health authorities. A traveler returning from Guatemala was found infected with the New World screwworm, a flesh-eating parasite long thought banished from American soil. According to Reuters, it is the first confirmed human case in the United States since the parasite began creeping north from Central America last year.A disturbing diagnosisThe case, disclosed last week on a CDC call with state veterinarians, has been confirmed but cloaked in secrecy. Officials said the patient has been treated and preventive steps are underway, but privacy laws have kept names, locations, and medical details hidden.The parasite from nightmaresThe screwworm fly earns its chilling name for good reason: its larvae burrow into open wounds, spiraling deeper into living flesh as they feed. Left untreated, the infestation can be fatal, with doctors often forced to extract hundreds of wriggling larvae from a single patient.Though humans can fall victim, the parasite’s main target is livestock and wildlife. And that’s what makes this Maryland case alarming.Why ranchers are on edgeThe US cattle herd is already at its smallest in seven decades, and beef prices are soaring. An outbreak of screwworms—once eradicated in the 1960s through a pioneering sterile fly program—could devastate the $100-billion beef industry. Experts warn billions of dollars in losses, food shortages, and further price spikes could follow if the parasite gains a foothold.Racing against timeThe Department of Agriculture is scrambling to contain the threat. Secretary Brooke Rollins announced plans for a new sterile fly plant in Texas, though it could take years to build. At present, the only operational facility is in Panama, producing 100 million sterile flies a week. Scientists say five times that number is needed to halt the northward march. Mexico, too, has launched a $51 million project to build its own defenses.