The United States Department of Health and Human Services (HHS) has confirmed the nation’s first human case of travel-associated New World screwworm, a flesh-eating parasite, in a patient who recently returned from El Salvador.
The case, verified by the Centers for Disease Control and Prevention (CDC) on August 4, was investigated in collaboration with the Maryland Department of Health, according to HHS spokesman Andrew G. Nixon. He stressed that “the risk to public health in the United States from this introduction is very low.”
The confirmation follows reports from industry sources claiming the CDC had earlier linked a Maryland case to travel from Guatemala, raising questions over conflicting accounts of the infection’s origin. Nixon did not comment on the discrepancies.
Screwworms are parasitic flies whose larvae invade the flesh of warm-blooded animals. While infestations can be fatal if untreated, human cases remain rare.
The development has alarmed US cattle ranchers and beef producers, who fear potential economic fallout should the parasite spread northward from Central America and southern Mexico. The US Department of Agriculture (USDA) has warned that a widespread outbreak could cost Texas — the nation’s largest cattle-producing state — an estimated $1.8 billion in livestock deaths, labour, and treatment expenses.
Beth Thompson, South Dakota’s state veterinarian, criticised the federal response, saying she only learned of the case through informal channels. “We found out via other routes and then had to go to CDC to tell us what was going on,” she told Reuters. “They weren’t forthcoming at all.”
Internal emails obtained by Reuters show the Beef Alliance alerted its members about the human case while noting that patient privacy laws restricted the release of details. The patient has since been treated, and containment measures have been put in place in Maryland.
In response to the growing threat, US Agriculture Secretary Brooke Rollins announced plans to establish a sterile fly production facility in Texas to curb the pest’s spread. Mexico, which reported new cases in July, has begun constructing a $51 million facility in the south of the country.
Currently, the only operational sterile fly plant is in Panama, producing about 100 million flies per week — far below the 500 million the USDA says are necessary to push screwworms back to the Darien Gap between Panama and Colombia.
The screwworm was eradicated from the US in the 1960s through mass releases of sterilised male flies, but its resurgence in Central America since 2023 has reignited fears of a renewed outbreak. A recent case in Mexico, just 370 miles south of the US border, forced the suspension of livestock trade at southern ports of entry.
Livestock traders caution that even the perception of a US screwworm outbreak could rattle already strained cattle markets, with the national herd at its lowest level in seven decades.
