Federal authorities have confirmed the first known U.S. case of the New World screwworm in nearly 60 years, raising concerns among agriculture and public health officials.
The discovery was made in a calf in Texas, marking the first confirmed domestic case since the parasite was eradicated from the United States in 1966.
What Exactly Is a Screwworm?
The New World screwworm is a parasitic fly whose larvae feed on living flesh. According to the Centers for Disease Control and Prevention, the flies lay eggs in open wounds or body openings of warm-blooded animals and, in rare cases, humans.
Once the eggs hatch, the maggots burrow into tissue and begin feeding, potentially causing severe and sometimes deadly damage if left untreated.
Officials Move Quickly to Contain It
U.S. Agriculture Secretary Brooke Rollins said federal and Texas officials are already working to contain and eradicate the parasite after it was discovered in a 3-week-old calf in Zavala County, Texas.
Authorities stressed that there are currently no additional confirmed cases in the United States.
Why Experts Are Taking This Seriously
Screwworm outbreaks once caused major losses for livestock industries before eradication efforts largely removed the parasite from the country decades ago.
The pest has continued to exist in parts of South America and has recently spread northward through Central America and Mexico, increasing concern among U.S. officials.
How the Parasite Spreads
Even small cuts or wounds can allow screwworm flies to lay hundreds of eggs at a time. The larvae then feed on living tissue for several days before dropping into soil and eventually becoming adult flies.
Health officials warn that infestations can rapidly worsen without medical or veterinary treatment.
Rare Human Cases Have Also Been Reported
While screwworm infections in humans are uncommon in the United States, officials previously confirmed a case involving a traveler returning from El Salvador in 2025.
The CDC advises people never to attempt removing deeply embedded larvae themselves and to seek medical care immediately if an infestation is suspected.
How Officials Previously Defeated the Pest
The USDA says one of the most successful historical strategies involved releasing sterile male flies to stop reproduction and gradually eliminate screwworm populations.
Officials say those same tools remain available if broader containment efforts become necessary.
Authorities Urge Vigilance
Agriculture officials are asking ranchers, veterinarians and the public to remain alert for unusual wounds or infestations in animals. Any suspected new cases are being encouraged to be reported immediately to federal authorities.
For now, officials say the situation appears contained, but the reappearance of the parasite after nearly six decades is drawing serious attention nationwide.
