The United States has recorded its first human case of the New World screwworm, a parasitic fly that infests flesh.
According to NBC News, the infected person had recently returned from El Salvador and is now under evaluation by the Maryland Department of Health and the U.S. Centers for Disease Control and Prevention.
According to Department of Health and Human Services spokesman Andrew G. Nixon, the infection was confirmed by the CDC on August 4. He reassured the public, stating, “The risk to public health in the United States from this introduction is very low.” Nixon also told Axios, “This is the first human case of travel-associated New World screwworm myiasis, parasitic infestation of fly larvae, from an outbreak-affected country identified in the United States.”
New World screwworm flies have been spreading north from South America in recent years. The female flies lay eggs on warm-bodied animals, including livestock. Humans are rarely affected, though infections can occur, particularly when the larvae find their way into open wounds or exposed areas.
Colin Woodall, CEO of the National Cattlemen’s Beef Association, explained to NPR, “The [fly] larva does exactly what the name would suggest. It screws or bores into the flesh of our cattle and, in essence, eats the animal from the inside out. It is a horrific parasite.”
The CDC has emphasized that the infestation is “very painful,” with maggots often visible or felt around the infection site.
In addition to skin wounds, larvae can infest a person’s nose, eyes, or mouth. Medical intervention is required to remove the larvae, which is sometimes achieved through surgery. Despite the pain, the infection is treatable and rarely fatal if addressed promptly.
However, untreated cases can pose serious health risks. The U.S. Department of Agriculture has taken steps to prevent the spread of the parasite.
On August 15, Secretary of Agriculture Brooke L. Rollins announced plans to release sterile male screwworms into the wild. NPR noted that because female screwworms mate only once, this approach can significantly reduce the population and the threat they pose.
These measures are part of a five-part strategy announced by the USDA in June 2025.
Previous reports by Reuters mentioned a Maryland resident infected after traveling to Guatemala, although it is unclear whether this involves the same individual. The Department of Health and Human Services referred inquiries about the patient to the Maryland Department of Health.
The emergence of this case serves as a reminder that parasites primarily affecting livestock can occasionally infect humans. Monitoring, early detection, and proper medical care are essential to controlling these infections and protecting public health.
