- The U.S. CDC confirmed the first human case of travel-associated New World screwworm in Maryland, linked to recent travel from Central America.
- Screwworms are parasitic flies that infest wounds on warm-blooded animals, posing serious risks to livestock and, rarely, humans.
- The USDA and Mexican authorities are increasing sterile fly production and border controls to prevent outbreaks, with Texas and southern Mexico as key focus areas.
- The cattle industry remains cautious amid record-high beef prices and limited transparency around human and animal cases, though eradication measures from the 1960s serve as a proven model.
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U.S. Confirms First Human Case of New World Screwworm
The U.S. Centers for Disease Control and Prevention has confirmed a human case of New World screwworm in Maryland, involving a traveler who had recently returned from Central America. While some industry sources identified Guatemala as the origin of the case, official statements from the U.S. Department of Health and Human Services indicated the patient had traveled from El Salvador. HHS emphasized that the risk to public health in the United States remains very low, and no animal cases have been reported this year.
The confirmation comes amid heightened concern within the cattle industry, which remains on alert for potential infestations as screwworm moves northward from Central America and southern Mexico. The differing reports between government sources and industry stakeholders have added to uncertainty among cattle ranchers, beef producers, and livestock traders.
This announcement follows the recent visit of U.S. Department of Agriculture Secretary Brooke Rollins to Texas, where she outlined plans to establish a sterile fly facility aimed at controlling the pest. The USDA has estimated that a screwworm outbreak could cost the Texas economy approximately $1.8 billion due to livestock losses, labor, and treatment expenses.
Industry groups and state officials learned about the case through various channels before official confirmation. Beth Thompson, South Dakota’s state veterinarian, noted that state authorities were informed of the case through indirect sources and subsequently had to coordinate with the CDC for verification. A Maryland state official also confirmed the case, while the Maryland Department of Health had not immediately provided comments.
Understanding Screwworms and Their Impact
Screwworms are parasitic flies whose females lay eggs in open wounds on warm-blooded animals. When the eggs hatch, the larvae burrow into living tissue using their sharp mouths, feeding screw being driven into wood—hence the name. If left untreated, infestations can be fatal.
These pests pose a serious threat to livestock and wildlife and, though rare, can also infest humans. Treatment involves the careful removal of larvae and thorough wound disinfection. Early intervention significantly increases the chances of survival.
In the confirmed U.S. case, patient privacy laws limited the release of details. The individual was treated promptly, and preventive measures were implemented within the state. According to industry communications, the CDC reported the case to Maryland health authorities, the state veterinarian, and relevant agricultural stakeholders to minimize risk.
The beef industry remains vigilant, particularly in light of measures such as the border closure to Mexican cattle, which has been largely in place since November to prevent screwworm entry. Industry representatives remain cautiously optimistic that, with awareness largely restricted to officials and veterinarians, the likelihood of further exposure or market disruption remains low.
Effects on Beef and Cattle Markets
Livestock traders and beef producers remain cautious as the potential for screwworm cases in cattle could affect a market already facing record-high prices, driven by the U.S. cattle herd reaching its smallest size in seven decades. The confirmation of a human case, coupled with limited transparency, presents additional challenges for USDA Secretary Brooke Rollins. While the USDA has implemented border traps and deployed mounted officers, some producers and analysts have criticized the agency for not acting sooner to increase sterile fly production.
Rollins first announced plans in June to build a sterile fly facility at Moore Air Force Base in Edinburg, Texas, near the site of a production plant used during the last major outbreak 50 years ago. The facility is expected to be operational within two to three years. In parallel, Mexico has invested $51 million in a southern sterile fly production facility to limit the spread of the pest, which can kill livestock within weeks if untreated.
Currently, the only operational plant is in Panama City, capable of producing 100 million sterile screwworm flies per week. USDA estimates indicate that 500 million flies would need to be released weekly to push the pest back to the Darien Gap between Panama and Colombia.
Screwworms have been moving northward through Mexico from Central America since 2023 and remain endemic in Cuba, Haiti, the Dominican Republic, and parts of South America. A new case was reported in July in Veracruz, Mexico, prompting the USDA to close southern ports of entry to livestock trade. The U.S. typically imports over a million Mexican cattle annually for feedlots and beef production.
Screwworms were eradicated from the United States in the 1960s through large-scale releases of sterilized male flies, which mate with wild females to produce infertile eggs, demonstrating the effectiveness of this biological control method.
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Source: Reuters
