- A human case of New World screwworm infestation was reported in the U.S. related to travel.
- Screwworm flies lay eggs in the wounds of nasal passages of warm-blooded animals.
- The larvae use the hooks on their mouths to burrow or screw their way deeper into wounds.
The New World screwworm has for the first time in years infested a human in the U.S. and federal officials are working to prevent the parasitic creature from getting into the food supply.
The U.S. battled an infestation of the screwworm decades ago and earlier this year closed the southern border to livestock imports over fear U.S. livestock could be infested, as Deseret News earlier reported.
Under an emergency use authorization, the U.S. Food and Drug Administration is allowing use of animal drugs to treat or prevent infestations, noting the authorization applies “only to drugs for animals.”
Per the notice, “Although eradicated from North America and Central America decades ago, NWS has progressed north since 2022 and is now approaching the U.S. border with Mexico. This parasite poses an emerging threat to livestock and food security, with potential impacts on both national security and animal health.”
“Today we are taking decisive action to safeguard the nation’s food supply from this emerging threat,” said Health and Human Services Secretary Robert F. Kennedy Jr. in the press release from the FDA. “This authorization equips FDA to act quickly, limit the spread of New World screwworm, and protect America’s livestock.”
What is New World screwworm?
New World screwworms — often called simply NWS — are the larvae of the New World screwworm fly, which may deposit its eggs in the wound of a warm-blooded animal. The eggs hatch and the maggots use their sharp mouth hooks to twist their way deeper into the wound, enlarging it — hence the name. They literally operate like a screw in wood as they eat their way into the flesh. The damage to the animal can be severe and even lethal. Untreated, the animal dies.
The U.S. Department of Agriculture has noted that they can infest livestock, pets, wildlife, birds (less common) and “in rare cases,” humans.
According to the Centers for Disease Control and Prevention, they are endemic in South America and the Caribbean.
The CDC notes that besides open wounds, the eggs may be deposited in “body cavities with mucus membranes” such as nasal passages. There’s no treatment aside from prevention and quick removal.
Reuters reported that the person that was infested is the first case of someone from the U.S. being infested after travel and said the case is connected to an ongoing Central American outbreak. There’s some question as to whether the individual, who is a Maryland resident, had traveled to El Salvador or Guatemala, per the article.
Battling parasitic flies
U.S. Department of Agriculture Secretary Brooke Rollins recently traveled to Texas to announce plans to spend up to $750 million to build a facility to produce sterile flies, which is a proven method to battle the parasitic fly.
“The plan signals increasing worries about the risk of screwworm, a parasitic fly that eats livestock and wildlife alive, to infest U.S. cattle after the pest moved north in Mexico toward the U.S. border,” Reuters separately reported.
“It could truly crush the cattle industry,” Texas Gov. Greg Abbott said at the news conference with Rollins.
Texas is the largest cattle-producing state and an outbreak could cost its economy as much as $1.8 billion should an infestation take hold. It would also likely raise the price of beef.
The U.S. border with Mexico was closed to livestock imports in November. But officials admitted at the time that the screwworm could still cross the border through natural wildlife movement. As Deseret News reported, “In February, the two countries agreed to a “comprehensive pre-clearance inspection and treatment protocol" to protect the trade and contain the fly larvae spread."
IFL Science reported that Moore Airbase in Texas will become a “fly factory — a facility that it’s claimed will produce up to 300 million sterile flies every week. It’s set to work alongside similar facilities in Panama and Mexico, with the latter receiving $21 million in funding from the USDA for renovations that will see it produce an extra 60 to 100 million sterile flies.”
Sterile flies were used in the 1960s during a previous infestation. The sterile flies mate with wild female flies, which don’t produce offspring. Over time, the New World screwworm fly population was eliminated.
Health effects of screwworm infestation
Screwworm flies look like common houseflies, but have orange eyes and metallic green or blue bodies and three dark stripes on their back.
Animals that have been infested may become irritable, smell like decaying flesh, have head shaking and have visible maggots in wounds.
According to Reuters in April, the first human case of screwworm in Mexico was successfully treated with antibiotics after the larvae were removed.