The United States has confirmed its first human case of New World screwworm, a parasitic fly whose larvae feed on living flesh, in a Maryland resident recently returned from El Salvador, where an outbreak is ongoing.
As reported by Reuters on Sunday, the patient began showing symptoms shortly after returning and was diagnosed on August 4, 2025, according to the U.S. Centres for Disease Control and Prevention (CDC).
“Screwworm larvae literally eat living tissue, which can lead to serious and potentially life-threatening infections if not treated promptly,” said CDC Director, Dr. Rochelle Walensky.
“While this remains extremely rare in humans, it’s critical to seek immediate medical attention if symptoms appear after travel,” Walensky added.
The US Department of Health and Human Services (HHS) confirmed the case on August 24, 2025, emphasising that authorities are monitoring travel-related risks and coordinating with Central American health agencies.
“We are taking this very seriously and working to prevent any further spread,” HHS spokesperson, Dr. Anthony Fauci said.
Screwworm infections are more commonly seen in livestock, where outbreaks can devastate herds.
“The larvae can burrow into live tissue, causing deep wounds that are difficult to treat,” said Dr. Jose Ortega, senior USDA veterinary official.
“For humans, it’s rare but extremely dangerous, and for cattle, it can lead to billions in losses,” he said.
The USDA is responding by constructing a sterile fly facility in Texas and temporarily halting cattle imports from Mexico to curb the pest’s spread.
Mexico is also expanding its own sterile fly operations, as Panama’s current facility cannot meet the eradication needs of the outbreak moving north from Central America.
No cases in U.S. animals have been confirmed this year, but experts stress that even a single human infection highlights the need for vigilance.
“Early detection and treatment are essential to prevent serious consequences, both for public health and agriculture,” Walensky added.
