Screwworm Detected in U.S. Human for First Time in Decades

Public health officials have confirmed a startling development: a human in Maryland has been diagnosed with the New World screwworm parasite—marking the first such case in the United States in decades. The patient had recently returned from El Salvador, where ongoing outbreaks have raised health and agricultural concerns.

What Is the Screwworm and Why It Matters

The New World screwworm (Cochliomyia hominivorax) is a type of parasitic fly whose larvae burrow into living tissue. While most often affecting livestock—including cattle, pets, and wildlife—it can, in rare cases, infest humans. The larvae feed on healthy flesh, which can lead to serious tissue damage if not treated promptly.

This parasite was largely eradicated from the U.S. by the early 1980s through a pioneering insect sterilization program. But recent outbreaks in Central America and Mexico have prompted renewed vigilance from U.S. agencies.

U.S. Officials Confirm the Case and Sound the Alarm

The Maryland Department of Health and the Centers for Disease Control and Prevention confirmed the screwworm diagnosis on August 4, based on expert review of submitted larvae images.

Although there was early confusion—some industry sources suggested the patient had traveled from Guatemala—officials clarified the patient’s travel history points to El Salvador.

Federal agencies emphasize that public health risk remains very low, stressing that the parasite does not spread from person to person.

Measures Underway to Stop the Threat

To prevent further spread, officials are reviving methods first used decades ago: releasing sterile male screwworm flies to reduce reproduction among wild populations. A new sterile fly production facility in Texas is in the works, with another planned in southern Mexico.

Additionally, agricultural authorities are monitoring livestock—and have imposed import restrictions on animals from affected regions near the U.S.–Mexico border.

Why the Screwworm Matters—Economically and Politically

While human cases are extremely uncommon, the screwworm poses a significant threat to the livestock industry. Officials estimate that an outbreak in Texas could cost the cattle industry up to $1.8 billion in lost livestock, treatment, and labor.

The health scare has also fueled criticism that federal agencies, including the USDA, have been slow to respond—raising concerns among ranchers and supply chain stakeholders.