First U.S. Case of Flesh-Eating Screwworm Confirmed
Federal health officials have confirmed the first human case of the flesh-eating “New World screwworm” parasite in the United States, raising concerns about the potential threat to both people and livestock. The Department of Health and Human Services (HHS) announced Monday that the infection, linked to recent travel to El Salvador, was confirmed by the Centers for Disease Control and Prevention (CDC) and the Maryland Department of Health on August 4.
The First Confirmed Human Case
According to Maryland health officials, the infected resident has since recovered, and investigations determined there was no risk of transmission to other individuals or animals. HHS spokesperson Emily G. Hilliard stressed that this is the first documented case of travel-associated New World screwworm myiasis — a parasitic infestation of fly larvae — in the U.S.
“The risk to public health in the United States from this introduction is very low,” Hilliard said.
While human cases are rare, they can be fatal if untreated. Most infections, however, respond to proper medical care.
What Is the Screwworm Parasite?
The screwworm, scientifically known as Cochliomyia hominivorax, is the larval form of the New World screwworm fly. Unlike typical flies, female screwworms lay eggs in the wounds or soft tissue of warm-blooded animals. Once hatched, hundreds of larvae burrow into flesh with sharp, screw-like mouths, consuming living tissue. This destructive process can cause severe injury, secondary infections, and even death in untreated cases.
The parasite poses a far greater threat to livestock and wildlife than to humans. Outbreaks can devastate cattle herds, spread rapidly in the wild, and even kill household pets.
A History of Outbreaks
The New World screwworm has a history of catastrophic outbreaks in Central America, with major infestations in the 1980s and 1990s. Eradication campaigns, which involved the release of sterilized male flies to collapse breeding populations, eventually eliminated the pest at enormous financial cost. However, in recent years, the parasite has returned to parts of Central America and Mexico.
The fly is considered endemic in Cuba, Haiti, the Dominican Republic, and several South American nations. Its steady northward spread has worried U.S. agriculture officials for years. In July, Mexico reported a case in Ixhuatlán de Madero, Veracruz—just 370 miles from the Texas border. That prompted immediate suspensions of cross-border cattle trade by the Department of Homeland Security, following earlier shutdowns in November and May.
The U.S. Response
U.S. Secretary of Agriculture Brooke L. Rollins announced a five-part plan on August 15 to combat the parasite’s spread. Central to the strategy is the mass release of sterilized screwworm flies across southern Texas and Mexico. When sterile males mate with wild females, the eggs fail to hatch, reducing populations over time. This method successfully eradicated screwworms in the U.S. during the 1960s.
The program, however, was initially projected to take “two to three years” before becoming fully operational—a timeline some officials argue must be accelerated.
Texas Governor Greg Abbott has been outspoken about the risks, citing the state’s $867 billion agriculture industry and its two million jobs. “All of this is at risk because of the New World screwworm,” Abbott warned.
A 2024 USDA report estimated that an uncontrolled screwworm outbreak in Texas could cost at least $1.8 billion in livestock deaths, veterinary care, labor, and treatment expenses.
Public Health Risk Remains Low
Despite the alarming headlines, experts emphasize that the risk of widespread human infection remains extremely low. Cases of human screwworm infestations are rare and treatable when promptly identified. Still, the parasite’s presence so close to U.S. borders has renewed urgency around prevention efforts.
The Maryland case, while isolated, underscores the importance of surveillance and rapid response. Health agencies are reminding clinicians to be alert for unusual parasitic infections in patients returning from affected regions.
For now, officials say the U.S. public should not be alarmed but remain informed. The focus remains on protecting livestock, wildlife, and agriculture—the areas where screwworm infestations can cause devastating losses.
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