A terrifying flesh-eating parasite has invaded the United States for the first time since 1966. Commonly called a New World Screwworm (NWS), the parasite has been confirmed in Texas after advancing across Mexico for the past year.
What is the New World Screwworm?
The parasite lays hundreds of larvae in the wounds of animals and humans, which hatch within hours and consume their victims' tissue. NWS can also infest people and pets, but the risk to humans is low. However, these infestations can lead to deep, painful wounds that become infected and often result in death if left untreated.
First US Case in Decades
Agriculture Secretary Brooke Rollins said the case was in a three-week-old calf in LaPryor, about 50 miles from the Mexico border. A 12-mile quarantine zone has been established, prohibiting the movement of any warm-blooded animal, including pets, outside that zone without an inspection. Rollins stated there have been no other detections of the fly in the US, and officials were quick to note that while the fly's larvae threaten livestock production, they do not infest food.
State and Federal Response
Texas Governor Greg Abbott issued a disaster declaration in February as screwworms threaten the state's booming beef industry, giving the state greater authority, resources, and speed to confront the growing threat. When screwworms became a major problem in the US, it cost the US $200 million (roughly $1.8 billion today) in livestock.
The announcement came only a day after Rollins held an online news conference to highlight the proximity of the threat, with cases confirmed in Mexico as close as 25 miles from the border, and to outline the US Department of Agriculture's (USDA) efforts to combat it. The months of effort to keep the parasite out of the US have included dropping millions of sterile screwworm flies in the area to mate with wild females. This is the same method used successfully before the NWS was eradicated.
Officials Express Confidence
Rollins said the USDA is confident enough in its preparations that it believes 'there is no threat of mass infestation.' 'There is no reason to believe this incursion will result in the establishment of the pest in our country,' Rollins added.
The Florida Department of Agriculture and Consumer Services found larvae in an open wound on a horse imported from Argentina in February. The horse was immediately quarantined. 'The New World Screwworm was eradicated from the US more than four decades ago,' Florida officials announced. 'Its return would pose a serious threat to livestock, wildlife, and domestic animals, particularly in states like Florida with warm climates and abundant animal populations.'
Texas Officials Urge Vigilance
Texas Agriculture Commissioner Sid Miller cautioned Florida residents not to panic. 'I want to set the record straight on the recent New World Screwworm detection in Florida,' Miller said in a statement. 'This detection did not constitute evidence of a US outbreak or domestic New World Screwworm infestation. It was thankfully caught during a routine inspection of an imported horse arriving from a country south of the Darien Gap.' However, he urged Texas ranchers and families to remain vigilant along the southern border and continue to routinely inspect all warm-blooded animals, including livestock, wildlife, and pets, and report any suspicion of larvae infestation immediately. 'This is a serious risk to our livestock industry and one that the Texas Department of Agriculture has been preparing for through our own heightened surveillance, coordination, and response planning,' said Miller. 'The New World screwworm is inching closer to Texas each and every day, and we must be proactive in responding to this threat.'
How the Parasite Attacks
The screwworm begins its attack when a female fly lays her eggs in an open wound or body orifice. These flies are attracted to the scent of exposed tissue and openings, which can be as small as a tick bite, a nasal or eye passage, a newborn's navel, or genital areas, according to the Texas Parks and Wildlife Department (TPWD). Once laid, the eggs hatch into larvae that burrow into the flesh like tiny screws, the agency said. A single female can lay 200 to 300 eggs at a time and as many as 3,000 over her lifetime. Infestations may also become visible on the skin.
Previous Human Case
In 2024, an unnamed patient in Maryland recently returned to the US from El Salvador and had been infested with the parasite. Department of Health and Human Services officials revealed the case but stressed that the risk to the public was 'very low'. The infection was first reported by Maryland officials and at the CDC on August 4. The worms were eliminated in the US in 1966, but sporadic cases have been detected since amid outbreaks in Central America. The latest case is not the first case ever in the US, but the first case in an individual who had traveled to the US from a country battling an outbreak.
