WASHINGTON — Federal health officials have confirmed the first known U.S. case of a human infection from the flesh-eating New World screwworm parasite, a dangerous insect species long considered eradicated in North America.
The U.S. Department of Health and Human Services (HHS) announced that the patient, who recently returned from El Salvador, was diagnosed on Aug. 4 with New World screwworm (NWS) myiasis, an infestation of fly larvae that consume the living tissue of animals and, in rare cases, humans. The BBC first reported the case Monday.
What Is the Screwworm Parasite?
The screwworm fly (Cochliomyia hominivorax) lays its eggs in open wounds or soft tissue. When the eggs hatch, larvae burrow into flesh, causing extensive tissue damage. If untreated, infestations can lead to severe illness or even death.
While screwworm outbreaks primarily affect livestock and wildlife, humans can also become infected if exposed in regions where the parasite is active. According to the Centers for Disease Control and Prevention (CDC), people with untreated wounds or who travel to rural areas with high livestock density are at higher risk.
“This is the first human case of travel-associated New World screwworm myiasis identified in the United States,” HHS spokesperson Andrew Nixon said, emphasizing that the overall public health risk in the U.S. remains “very low.”
Spread Across Central America
The screwworm parasite is typically found in South America and the Caribbean. Despite aggressive eradication efforts, cases have been confirmed in every Central American country in recent years, including Mexico, raising fears of northward expansion.
The U.S. Department of Agriculture (USDA) noted earlier this month that an outbreak in livestock could cause severe economic disruption, threatening more than $100 billion in cattle and livestock-related industries.
“When NWS fly larvae burrow into the flesh of a living animal, they cause serious, often deadly damage,” the USDA’s Animal and Plant Health Inspection Service explained in a statement. The agency has partnered with international groups, including the Food and Agriculture Organization of the United Nations, to contain the parasite’s spread.
Case Investigation and Response
In this case, the CDC worked alongside Maryland’s Department of Health to confirm the infection after the patient returned from El Salvador, one of the countries currently experiencing outbreaks.
Authorities have not disclosed the patient’s identity or condition but stressed that immediate treatment reduces the risk of severe complications.
Potential Risks and Safeguards
Although rare, human infections highlight the parasite’s threat if it re-establishes in U.S. soil. The screwworm was previously eradicated from the U.S. in 1982 through an extensive program that released sterile male flies to collapse the breeding population.
Re-introduction, however, remains a concern. Agricultural officials warn that even a small outbreak among livestock could escalate quickly, requiring aggressive eradication measures.
“Even a single case, in either humans or animals, serves as a reminder of the vigilance required to prevent screwworm re-establishment,” said Dr. Emily Larsen, a veterinary epidemiologist at Texas A&M University.
Outlook
For now, officials maintain that the likelihood of widespread human infection in the U.S. is low. Still, health authorities are urging travelers to Central America and the Caribbean to take precautions — particularly covering open wounds, using insect repellents, and seeking immediate medical attention if unusual lesions or maggot infestations occur.
“This incident underscores the importance of coordinated animal and human health surveillance,” the USDA stated, noting that protecting livestock also protects communities.
The case comes as U.S. agencies balance agricultural biosecurity, global travel risks, and public health preparedness against a parasite that once posed one of the most destructive threats to North American livestock.