First Travel-Associated Human Screwworm Case Confirmed in the U.S.

First Travel-Associated Human Screwworm Case Confirmed in the U.S.

The United States has confirmed its first travel-associated human case of New World screwworm (NWS) infestation, marking a significant public health event. This case involved a Maryland resident who had recently traveled to El Salvador, a country currently experiencing an outbreak of the parasite. The detection of this flesh-eating parasitic infestation in a human within U.S. borders highlights emerging challenges in disease surveillance and control linked to global travel and animal health threats (source).

Introduction and Overview

New World screwworm, Cochliomyia hominivorax, is a parasitic fly species whose larvae feed on the living tissue of warm-blooded animals, including humans. The condition caused by these larvae is known as myiasis. While NWS primarily affects livestock, causing severe economic and animal welfare impacts, human cases have been rare and mostly reported in Central and South America and the Caribbean. The recent Maryland case is notable as it represents the first confirmed human infection in the U.S. linked to travel from an outbreak-affected country in recent decades.

The infected individual was diagnosed after returning from El Salvador, where NWS infestations have been increasing. The Centers for Disease Control and Prevention (CDC) confirmed the diagnosis in early August 2025, and the patient has since recovered without further transmission to others or animals. This case underscores the potential for travel to introduce parasitic diseases previously eradicated or controlled in the U.S. (source).

Key Aspects and Current Trends

NWS larvae are notorious for laying eggs in open wounds or body orifices, where the hatched maggots burrow into living flesh, causing painful and potentially life-threatening infections. Historically, the screwworm was a major problem for the U.S. livestock industry, especially in southern states like Florida and Texas, until eradication programs in the 1960s and 1970s successfully eliminated the parasite from the country.

However, the parasite remains endemic in parts of South America, Central America, and the Caribbean. In recent years, outbreaks have been reported in countries such as El Salvador, increasing the risk of reintroduction into the U.S. through travel or animal imports. The USDA has responded by suspending certain live animal imports at the southern border to reduce the risk of reintroduction.

The Maryland case is particularly significant because it demonstrates that human travel can serve as a vector for this parasite, even though human infections are rare compared to livestock infestations. Public health officials emphasize that the risk to the general U.S. population remains very low, but vigilance is necessary to prevent establishment or spread of the parasite within the country (source).

Main Challenges and Opportunities

The reemergence of NWS in a human case in the U.S. presents several challenges:

• Surveillance and Early Detection: Since NWS was eradicated decades ago in the U.S., awareness among healthcare providers about recognizing myiasis caused by screwworm larvae is limited. Early diagnosis is critical to prevent severe tissue damage and complications.
• Cross-Border Animal and Human Movement: Increased travel and trade between the U.S. and endemic regions raise the risk of parasite introduction. Managing this risk requires coordinated efforts between public health, agriculture, and customs agencies.
• Livestock Industry Vulnerability: The parasite poses a serious threat to cattle and other livestock, with infestations causing severe tissue damage and economic losses. The potential reintroduction could undermine decades of eradication efforts.
• Public Education and Preparedness: Informing travelers about the risks and symptoms of screwworm infestation, especially those visiting outbreak areas, is essential to prompt medical attention and containment.

On the opportunity side, the case has galvanized renewed attention and resources toward screwworm surveillance and control. The USDA has enhanced border inspections and animal import restrictions, and veterinary professionals are being equipped with better tools to identify and respond to screwworm cases. Additionally, the CDC and state health departments are collaborating to improve diagnostic capacity and public awareness.

The Maryland case also provides valuable data for research on human myiasis and the ecology of NWS, which can inform future prevention strategies. Advances in sterile insect technique (SIT) programs, which release sterilized male flies to reduce populations, remain a promising method for controlling and potentially eradicating screwworm populations in endemic regions, thereby reducing the risk of spread to the U.S.

Reflecting on the Implications

The confirmation of the first travel-associated human screwworm case in the U.S. after decades of eradication serves as a reminder of the interconnectedness of global health and the persistent threat posed by parasitic diseases. Although the immediate risk to public health is low, the incident highlights the importance of sustained vigilance, cross-sector collaboration, and public education to prevent reestablishment of this damaging parasite.

This event also underscores the need for robust surveillance systems that can detect and respond to emerging infectious threats linked to travel and trade. It calls for continued investment in research, veterinary and medical training, and international cooperation to safeguard both human and animal health.

The Maryland case is a pivotal moment that could drive improvements in how the U.S. monitors and manages parasitic infestations, ensuring that past successes in eradication are not reversed and that public health remains protected in an increasingly globalized world (source).