First U.S. Case of New World Screwworm Disease in Humans Confirmed

The U.S. Department of Health and Human Services (HHS) has validated the initial instance of New World screwworm infection in a human within U.S. borders. This parasitic disease, known for its devastating effects, is prevalent in certain Central American and South American countries but seldom affects humans. The infected individual had recently returned from El Salvador, which is currently experiencing an outbreak. Official confirmation came on August 4, following an examination by the Maryland Department of Health and the Centers for Disease Control and Prevention (CDC). Andrew G. Nixon, an HHS spokesperson, relayed this information to Reuters via email.

Reuters had previously reported the person was from Guatemala, but Nixon did not address this discrepancy, adding to the growing uncertainty, especially in the livestock sector. "The public health risk in the United States from this introduction is very low," Nixon assured, aiming to alleviate fears of a potential nationwide outbreak.

Understanding the Screwworm

The New World screwworm is a flesh-eating parasitic fly, scientifically known as Cochliomyia hominivorax. Female flies lay eggs in open wounds of animals or humans. Upon hatching, the larvae use sharp mouthparts to burrow and consume living flesh, leading to infections that can be fatal if untreated. The pest gets its name from the way the larvae embed themselves in the body, akin to a screw boring into wood. These infestations are particularly destructive to livestock and wildlife.

"Treatment is complex and involves removing hundreds of larvae and thoroughly disinfecting wounds," note the CDC. However, with early detection, the disease can be managed successfully. The human case identified in Maryland received appropriate treatment, and state authorities have implemented preventive measures, though details are withheld for privacy reasons.

Veterinary Sector Concerns Over Transparency

The case has stirred discontent within the veterinary and agricultural sectors due to the CDC's lack of transparency. Beth Thompson, the state veterinarian for South Dakota, mentioned that many learned of the case "through other channels" and had to pressure the CDC for information. "They were not transparent at all. They left it up to the state to confirm anything that may have occurred or been found in this traveler," Thompson told Reuters. Other state veterinarians also reported discovering the case through a CDC call, without direct or immediate notification.

A Marketplace on High Alert

The news breaks at a sensitive time for the American livestock industry. Cattle traders and meat producers are on edge over potential animal infestations, particularly with livestock prices reaching historic highs. The national cattle herd is at its lowest in seven decades. According to the U.S. Department of Agriculture (USDA), a screwworm outbreak could cost Texas's economy an estimated $1.8 billion in losses from animal deaths, labor costs, and veterinary treatments.

"We remain optimistic that, since awareness is currently limited to industry representatives and state veterinarians, the likelihood of a positive case leaking is low, minimizing the market impact," wrote an executive from the industrial group Beef Alliance in an internal email obtained by Reuters.

The Growing Threat from Central America

The screwworm was eradicated in the United States in the 1960s through a successful sterile male fly release program, a strategy still in use. However, since 2023, the pest has begun advancing again from Central America through Mexico. In July, Mexico reported a new case in Ixhuatlán de Madero, Veracruz, only 370 miles from the U.S. border. In response, the USDA ordered the closure of livestock trade through southern entry ports, intensifying a measure in place since November.

Currently, only one operational sterile fly production plant exists in Panama City, capable of producing 100 million specimens weekly. But the USDA estimates at least 500 million weekly are needed to contain the pest's spread southward, especially toward the Darién Gap between Panama and Colombia. Meanwhile, Mexico announced in July the construction of its own $51 million plant to produce these flies, while in the U.S., Agriculture Secretary Brooke Rollins announced plans for a new plant at Moore Air Force Base in Edinburg, Texas, although it won't be operational for another two to three years.

A Health and Political Challenge

This first human case could become a political issue for Secretary Rollins and health authorities if the pest isn't contained. Pressure is mounting among ranchers as the USDA faces criticism for its perceived slow response in expanding sterile fly production and securing the southern border. Additionally, discrepancies in information—such as the patient's country of origin (Guatemala or El Salvador)—and unclear management by the CDC have left a bitter taste among experts and local authorities.

While U.S. officials insist that the risk to the population is "extremely low," this first human screwworm case serves as an early warning of a potential health and economic crisis if animal outbreaks aren't contained. Historical experience shows that the disease can be eradicated with well-funded and coordinated strategies. But time is of the essence, and the multi-billion-dollar livestock industry cannot afford improvisation.

"An undetected infestation can kill cattle within weeks," warn USDA experts. With traps, mounted patrols at the border, and fly factories under construction, the United States seeks to prevent a once-defeated parasite from taking root again.