A menacing parasite known for consuming flesh has resurfaced in the United States, marking its first appearance since 1966.
Identified as the New World Screwworm (NWS), this parasite has recently been detected in Texas after making its way through Mexico over the past year.
The New World Screwworm is notorious for depositing hundreds of larvae into the wounds of both animals and humans. These larvae hatch rapidly, devouring the host’s tissue.
While the parasite poses a threat to animals and pets, the likelihood of human infection remains low. Nonetheless, infestations can cause severe, painful sores that can become infected and potentially fatal if not addressed.
According to Agriculture Secretary Brooke Rollins, the parasite was found in a three-week-old calf located in LaPryor, approximately 50 miles from the Mexican border.
In response, authorities have set up a 12-mile quarantine zone, restricting the movement of any warm-blooded creatures, including pets, without prior inspection.
Rollins said there have been no other detections of the fly in the US, and officials were quick to say that while the fly’s larvae are a threat to livestock production, they do not infest food.
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 needed to confront the growing threat posed by the parasite.
When screwworms became a major problem in the US, it cost the US $200 million – roughly $1.8 billion today – in livestock.
A terrifying flesh-eating parasite has invaded the US 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. Pictured are Texas cattle ranchers attending a presentation about the threat of the NWS
The announcement of the case comes 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.
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 said.
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.’
‘The New World Screwworm was eradicated from the US more than four decades ago,’ Florida officials announced.
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
‘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 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 Darién 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.
A test container of dyed fly pupae are displayed at a Domestic New World Screwworm Sterile Fly Production Facility to combat the northward spread of NWS and protect American livestock
‘The New World screwworm is inching closer to Texas each and every day, and we must be proactive in responding to this threat.’
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, KHOU 11 reported. Infestations may also become visible on the skin.
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.
