Health Officials Confirm First Human Case of Travel-Associated New World Screwworm in the U.S.
The U.S. Department of Health and Human Services announced on Sunday the first recorded human case of New World screwworm, a parasitic organism associated with outbreaks in specific countries, within the nation.
The Maryland Department of Health, in collaboration with the U.S. Centers for Disease Control and Prevention (CDC), confirmed on August 4 that the patient had recently traveled from El Salvador. HHS spokesperson Andrew G. Nixon conveyed this information via email to Reuters.
Previously, industry insiders reported that the CDC had identified a human case of New World screwworm in a Maryland resident who had traveled from Guatemala.
Nixon did not clarify the conflicting reports regarding the origin of the confirmed human case.
He emphasized that “the risk to public health in the United States from this introduction is very low.”
So far, the government has not identified any animal cases this year.
The contrasting narratives from government and industry sources regarding the human case may further unsettle cattle ranchers, beef producers, and livestock traders who are already vigilant about a potential infestation as the screwworm spreads from Central America and southern Mexico.
The government’s announcement relates to a week after U.S. Department of Agriculture Secretary Brooke Rollins visited Texas to outline initiatives to combat the pest, including plans to establish a sterile fly facility.
The USDA has indicated that an outbreak of screwworms could cost Texas — the country’s largest cattle-producing state — approximately $1.8 billion, factoring in livestock losses, labor costs, and medical expenses.
An executive with the Beef Alliance informed roughly two dozen individuals across the livestock and beef sectors last week that the CDC had confirmed a human case in Maryland related to travel from Guatemala, as per a source who chose to remain anonymous.
Beth Thompson, South Dakota’s state veterinarian, informed Reuters that she became aware of the Maryland human case within the last week. According to her, the CDC referred questions back to Maryland state officials during a recent call with animal health representatives. “We discovered it through other means and then sought confirmation from the CDC,” she noted, stating that the agency was not forthcoming.
Another informed source revealed that state veterinarians learned of the Maryland case during a discussion with the CDC last week. A representative from the Maryland government corroborated the human case.
A spokesperson for the Maryland Department of Health did not respond immediately to inquiries for comment.
What Are Screwworms?
Screwworms are parasitic flies whose larvae hatch in the wounds of warm-blooded animals. Once hatched, the larvae burrow into living flesh using sharp mouthparts, which can be fatal if untreated.
Their feeding behavior resembles a screw being driven into wood, hence their name.
Screwworm infestations can decimate cattle and wildlife populations and are rarely seen in humans. However, if either case occurs, it can be deadly.
Treatment is labor-intensive, necessitating the removal of numerous larvae and thorough wound disinfection. Timely treatment usually ensures survival.
The emails from the Beef Alliance executive noted that due to privacy laws, detailed information regarding the human screwworm case is restricted. The individual received treatment, and precautionary measures were undertaken in the state, according to these emails.
A livestock economist from Texas A&M University has been asked to prepare a report assessing the border closure’s impact on cattle imports from Mexico, which has predominated since November to avert the entry of screwworms.
The CDC is mandated to notify Maryland health officials and the state’s veterinarian upon confirming a positive New World screwworm case, as noted in one of the emails. The agency also informed other agricultural stakeholders.
“We remain optimistic that given awareness is currently confined to industry personnel and state veterinarians, the likelihood of a case being leaked is minimal, thereby reducing market disruption,” wrote the beef industry executive.
The Beef Alliance declined to provide further comments.
Effects on Beef and Cattle Markets
The livestock and beef industries are on high alert concerning the possibility of cattle infestations amid soaring prices due to the declining U.S. cattle herd, now at its lowest in 70 years.
The confirmation of a human case and the ensuing opacity may pose political challenges for Rollins. While the USDA has installed traps and dispatched mounted officers along the border, some cattle producers and market analysts have criticized the agency for not accelerating efforts to boost fly production.
Rollins earlier announced intentions to build a sterile fly facility at Moore Air Force Base in Edinburg, Texas. This location is near a facility that effectively battled screwworms during the last significant outbreak 50 years ago. The USDA spokesperson has yet to respond to requests for comment. Meanwhile, Mexico has undertaken measures to restrict the pest’s spread, establishing a $51 million sterile fly production facility in the southern region.
Currently, the only operational facility is located in Panama City, with a production capacity of 100 million sterile flies weekly. The USDA estimates that approximately 500 million flies would need to be released every week to push the infestation back to the Darien Gap, the rainforest between Panama and Colombia.
Since 2023, screwworms have been advancing northward through Mexico from Central America. They are already present in Cuba, Haiti, the Dominican Republic, and various South American nations, as documented by the USDA.
In July, Mexico reported a new case approximately 370 miles south of the U.S. border in Ixhuatlan de Madero, Veracruz. Following this, the USDA mandated a halt to livestock trading through southern ports of entry, having previously suspended imports in November and May.
The United States typically imports over one million cattle annually from Mexico for feeding and processing into beef.
Screwworms were eradicated from the United States in the 1960s, following the release of large quantities of sterilized male flies that mated with wild females, resulting in infertile eggs.
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