First U.S. Case of New World Screwworm Parasite Linked to Travel to Central America

A recent case in the United States has brought attention to the presence of the New World screwworm parasite, a fly known for its larvae that infest open wounds and bodily orifices. The individual, who traveled to El Salvador — a country currently experiencing an outbreak of this parasite — was diagnosed with the infection. The Centers for Disease Control and Prevention (CDC) confirmed the diagnosis on August 4, 2025. While the specific details of the patient's condition have not been publicly disclosed, this case marks the first known instance of the parasite in the U.S. associated with travel-related exposure.

The New World screwworm is a parasitic fly that typically lays its eggs in open wounds, including areas like the eyes, ears, nose, and mouth. Although it primarily affects livestock, infections in humans are rare. Importantly, the parasite does not transmit from person to person, which means it poses a limited risk to the general public. However, its presence is a significant concern for the agricultural sector, especially cattle ranching.

Historically, this parasite was a major threat to American cattle, leading to extensive control efforts until the 1970s, when the U.S. eradicated it. Recently, though, there are concerns about its northward movement through Central America and Mexico, highlighting the importance of ongoing surveillance and prevention measures.

U.S. health and agricultural officials, including the CDC and the U.S. Department of Agriculture, are actively working together to monitor and prevent the spread of the parasite. Efforts include tracking cases, controlling outbreaks in livestock, and preventing further human infections. This incident underscores the importance of travelers exercising caution and of continued vigilance to safeguard both health and agriculture in the region.