First U.S. Human Case of Travel-Linked Screwworm Confirmed by HHS

• Aug 25, 2025

The U.S. has confirmed its first human case of New World Screwworm infestation linked to international travel, health officials announced. The case was identified in a patient who had recently returned from El Salvador and later tested positive for the parasite.

According to the Department of Health and Human Services (HHS), the Centers for Disease Control and Prevention (CDC) confirmed the case on August 4, working closely with Maryland’s health department. “This is the first human case of travel-associated New World screwworm myiasis from an outbreak-affected country identified in the United States,” said HHS spokesperson Andrew Nixon. He emphasized that the current risk to the U.S. public remains “very low.”

New World Screwworm myiasis is caused by parasitic flies whose larvae, or maggots, feed on the flesh of living animals. The larvae burrow into open wounds or natural body openings such as the nostrils, eyes, or mouth, causing painful infestations that can expand wounds and, if untreated, may lead to severe tissue damage or even death. The U.S. Department of Agriculture (USDA) warns that while livestock, pets, and wildlife are the most common victims, humans can also be infected in rare cases.

The condition is most common in South America and the Caribbean, particularly in rural regions where livestock is raised. The CDC notes that people with open sores, wounds, or other vulnerabilities face greater risk of infection. Currently, there is no medication to treat New World Screwworm; instead, infestations must be managed through medical or veterinary intervention to remove larvae.

Concerns about the spread of screwworms have been rising in recent years. Late in 2024, Texas authorities issued an advisory after the parasite was found in cattle in southern Mexico’s Chiapas state. Officials warned that the pest had been moving north through the Americas, prompting a call for farmers and pet owners near the Texas border to monitor animals closely for signs of infection.

In June, the U.S. government unveiled a new policy initiative designed to prevent the spread of New World Screwworm through livestock and animal imports. Plans include building an insect dispersal facility in Texas as part of wider efforts to protect the country’s agriculture and wildlife.

While this case marks the first travel-related human infection in the U.S., health experts say strict monitoring and prevention measures remain essential to limit future risks.