It’s the kind of headline that makes you shudder: the first human case of New World screwworm, a flesh-eating parasitic fly, has been confirmed in the United States. Health officials in Maryland reported earlier this month that a resident had contracted the rare and dangerous parasite, marking the first time such an infection has been documented in a human on U.S. soil, according to the Centers for Disease Control and Prevention (CDC).
For many Americans, the words “screwworm” might conjure up images from a horror movie. But for veterinarians, livestock producers, and global health experts, the threat is all too real. The New World screwworm, scientifically known as Cochliomyia hominivorax, is a species of fly whose larvae feed on the living tissue of warm-blooded animals. The parasite was once a devastating pest across the southern United States, but decades of aggressive eradication campaigns had relegated it to the history books—until now.
According to the CDC, the Maryland patient had recently traveled to Central America, where the New World screwworm is still endemic. State veterinarians were notified of the case during a call with the CDC in mid-August 2025, as reported by NAFB News Service. The infected individual returned to Maryland, where symptoms began to emerge: painful, unexplained skin lesions that refused to heal, bleeding from open sores, and, most disturbingly, the sensation of larvae moving within the wound. In some cases, maggots may be visible in the wound or even in the nose, mouth, or eyes, accompanied by a foul-smelling odor.
“New World screwworm is a devastating pest,” the United States Department of Agriculture (USDA) warns. The fly’s larvae are notorious for their destructive feeding behavior, burrowing into wounds like a screw twisting into wood. As they tunnel deeper, they tear at the host’s tissue with sharp mouth hooks, causing wounds to expand, deepen, and become increasingly painful. If left untreated, the infestation can lead to severe tissue damage and, in rare cases, death.
While the parasite primarily targets livestock, pets, and wildlife—occasionally even birds—humans are not immune. People who travel to South America and the Caribbean, where the screwworm remains a persistent threat, are considered at higher risk for infestation. The CDC emphasizes the importance of prevention, especially for travelers to tropical regions or those spending time outdoors. Their advice: prevent insect bites, keep open wounds clean and covered, wear loose-fitting, long-sleeved shirts and pants, use EPA-registered insect repellents, and treat clothing and gear with products containing 0.5% permethrin. Sleeping indoors or in screened rooms is also recommended.
Once inside a host, the screwworm larvae can wreak havoc. The CDC lists a range of symptoms: unexplained skin lesions or sores that do not heal, wounds that worsen over time, persistent pain, bleeding, the unmistakable feeling of larvae movement, and maggots visible in or around open sores. The odor emanating from the site of infestation is often described as foul and unmistakable. These symptoms should prompt immediate medical attention, as the only effective treatment is surgical removal of the larvae. “Your healthcare provider will remove the larvae through surgery,” the CDC states plainly.
State and federal officials acted quickly to contain the Maryland case. According to Oklahoma State Veterinarian Dr. Rod Hall, authorities are confident that the infection is contained within Maryland. Dr. Hall noted, “I believe the U.S. is probably more likely to get it in a person or pet than in livestock, at least in the short term.” South Dakota State Veterinarian Beth Thompson told Reuters that the CDC worked closely with local physicians to identify and remove the larvae from the patient. No livestock movement restrictions have been imposed in Maryland, but the USDA has taken the precautionary step of restricting the importation of cattle, horses, and bison from Mexico, aiming to prevent the screwworm’s reintroduction to American herds.
The stakes are high. The New World screwworm was once widespread across the southern United States, causing untold losses to the livestock industry. Through a landmark collaboration between the USDA and international partners, the parasite was largely eradicated from U.S. livestock decades ago. The key to this victory was the sterile insect technique, a method still considered the gold standard for eradication. As the USDA explains, “Sterile male flies are released into an area where a known population has become established. The sterile male flies mate with wild female NWS flies, which then lay unfertilized eggs. Because female NWS flies mate just once in their lifespan, the NWS population progressively reduces and ultimately dies out.”
But eradication is no guarantee of permanent safety. The parasite still thrives in parts of South America and the Caribbean, and with global travel and trade, the risk of reintroduction remains ever-present. The Maryland case is a stark reminder of how quickly old threats can reemerge. As one Reuters article noted, the U.S. government is working to prevent a resurgence of an insect “largely eradicated from livestock decades ago.”
For the average American, the risk of contracting New World screwworm remains extremely low. But for travelers, pet owners, and livestock producers—especially those in border states or with international connections—vigilance is crucial. The CDC and USDA both stress the importance of early detection and prompt treatment. Animals suspected of infestation should be treated by a veterinarian, while people with suspicious wounds or symptoms should seek immediate medical care.
Officials are keen to reassure the public. The Maryland case appears to be isolated, and there is no evidence of a broader outbreak. Nevertheless, the incident has prompted renewed efforts to educate healthcare providers, veterinarians, and the public about the signs, symptoms, and prevention of screwworm myiasis. As the CDC and USDA continue their surveillance and prevention campaigns, the hope is that this rare human case will remain just that—rare, contained, and ultimately, a lesson in the importance of vigilance against even the most unlikely of adversaries.
For now, the story of the Maryland screwworm case serves as a vivid reminder: in the world of infectious diseases, history has a way of repeating itself, and complacency is never an option.
