US Detects Its First Case of Flesh-Eating Screwworm in a Human

A case of the flesh-eating screwworm parasite has been identified in a person in Maryland who had traveled to the United States from Guatemala, according to four sources familiar with the situation.

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BUENOS AIRES/CHICAGO —

The person, who received treatment in Maryland, is the first confirmed case in the US of New World screwworm, a parasite that eats cattle and other warm-blooded animals alive, since an outbreak began to escalate and move northwards from Central America and southern Mexico late in 2024.

Dr. Beth Thompson, South Dakota's state veterinarian, told Reuters on Aug. 24 that she was notified of the case within the last week by a person with direct knowledge of the Maryland case.

A second source, who asked not to be identified, said they had seen emails sent by an executive of industry group Beef Alliance on Aug. 20 to about two dozen people in the livestock and beef sectors, informing them that the US Centers for Disease Control and Prevention (CDC) had confirmed a case of screwworm in Maryland in a person who had traveled to the US from Guatemala.

State veterinarians learned about the human case in Maryland during a call last week with the CDC, according to one source. A Maryland state government official also confirmed the case.

CDC deferred questions to Maryland on a call with state animal health officials, Dr. Thompson said. "We found out via other routes and then had to go to CDC to tell us what was going on," she said. "They weren't forthcoming at all. They turned it back over to the state to confirm anything that had happened or what had been found in this traveler."

A CDC spokesperson and a spokesperson for the Maryland Department of Health did not immediately respond to requests for comment.

The confirmed case comes just over a week after US Department of Agriculture (USDA) Secretary Brooke Rollins and other government officials traveled to Texas to announce plans to build a sterile fly facility there as part of efforts to combat the pest.

WHAT ARE SCREWWORMS?