A New Threat: Flesh-Eating Screwworm Identified in the U.S.
A case of the flesh-eating screwworm parasite has been confirmed in a person in Maryland who had recently traveled from Guatemala, marking the first known human infection in the United States since an outbreak began to spread northward from Central America and southern Mexico. The individual received treatment in Maryland and is now under medical care. This development has raised concerns among state veterinarians and industry leaders due to the potential risks associated with the parasite.
Beth Thompson, South Dakota’s state veterinarian, shared information about the case after being informed by someone directly involved in the situation. She mentioned that the case was brought to her attention within the last week. Another source, who chose to remain anonymous, revealed that emails were sent to members of the livestock and beef sectors on August 20, confirming the presence of a human screwworm case in Maryland. These communications were part of broader efforts to alert stakeholders about the growing threat.
State veterinarians learned about the case during a recent call with the Centers for Disease Control and Prevention (CDC), as confirmed by one of the sources. A Maryland state government official also verified the case. However, the CDC did not provide direct responses to questions, instead directing officials to the state for more information. According to Thompson, “We found out via other routes and then had to go to CDC to tell us what was going on. They weren’t forthcoming at all.”
The CDC and the Maryland Department of Health have not responded to requests for comment. Meanwhile, the Beef Alliance, an industry group, has been actively communicating with stakeholders about the situation. Their emails highlighted the importance of early detection and prevention measures, emphasizing that the case had been confirmed on August 20. Despite these efforts, details about the patient remain limited due to privacy laws.
Understanding Screwworms
Screwworms are parasitic flies whose females lay eggs in wounds on warm-blooded animals. Once the eggs hatch, the larvae feed on living tissue, causing severe damage if left untreated. This feeding process resembles a screw being driven into wood, which is how the pest got its name. While primarily affecting cattle and wildlife, rare cases of human infestation have been reported. If not treated promptly, the infestation can be fatal.
Treatment involves removing hundreds of larvae and thoroughly disinfecting the wound. Early intervention significantly improves the chances of recovery. The presence of this parasite in the U.S. has sparked concern, particularly given the economic impact on the beef and cattle industries.
Economic and Political Implications
The confirmation of a screwworm case in the U.S. could have significant implications for the beef and cattle futures market, which has already experienced record-high prices due to tight supplies. With the U.S. cattle herd at its smallest size in seven decades, any disruption could lead to further price volatility.
U.S. Department of Agriculture Secretary Brooke Rollins has faced scrutiny over the handling of the outbreak, especially after pledging to keep the parasite out of the country. The USDA has taken steps such as setting traps along the border and deploying mounted officers, but some producers and analysts have criticized the pace of action. In June, Rollins announced plans for a sterile fly facility in Texas, aiming to combat the issue. However, the facility is expected to take two to three years to become operational.
Mexico has also implemented measures to control the spread of the parasite, including building a $51 million sterile fly production facility. The current plant in Panama City can produce up to 100 million sterile flies weekly, but experts estimate that 500 million would need to be released weekly to contain the infestation in the Darien Gap region.
Broader Impact and Ongoing Efforts
Screwworms have been spreading north through Mexico from Central America since 2023. The parasite is endemic in several countries, including Cuba, Haiti, and the Dominican Republic. In July, Mexico reported a new case near the U.S. border, prompting immediate restrictions on livestock trade through southern ports. The U.S. typically imports over a million cattle from Mexico annually for processing.
The parasite was eradicated from the U.S. in the 1960s through the release of sterilized male flies, which prevented reproduction. However, the current outbreak poses a serious threat, with the USDA estimating potential losses of up to $1.8 billion in Texas alone if an outbreak occurs.
As the situation continues to unfold, the focus remains on containment, transparency, and long-term strategies to prevent the spread of this dangerous parasite.
