The first human case of the flesh-eating New World screwworm parasite has been confirmed in the United States, according to the Department of Health and Human Services (HHS).
The case involves a patient who had recently traveled to El Salvador and was diagnosed with screwworm infestation—formally known as myiasis—on August 4. The diagnosis was confirmed by the Centers for Disease Control and Prevention (CDC) and the Maryland Department of Health.
“This is the first travel-associated human case of New World screwworm myiasis from an outbreak-affected country to be identified in the U.S.,” said HHS spokesperson Emily G. Hilliard. She emphasized that the overall risk to public health in the U.S. remains very low.
The parasite, the larvae of the New World screwworm fly (Cochliomyia hominivorax), is known to cause severe damage to livestock, wildlife, and pets by burrowing into the flesh of warm-blooded animals. The infestation can be fatal if untreated.
Historically, major outbreaks occurred across Central America during the 1980s and 1990s before the pest was eradicated through extensive and costly control efforts. However, the parasite has reemerged in recent years and has been spreading northward from Central America into Mexico.
In response to the growing threat, U.S. Secretary of Agriculture Brooke L. Rollins traveled to Texas on August 15 to announce a five-part strategy aimed at containing the screwworm. Central to the plan is the mass breeding and aerial release of sterile male flies over southern Texas and northern Mexico. These sterile males, when they mate with wild females, produce no offspring—gradually reducing the population over time. A similar method was successfully used during the last U.S. outbreak in the 1960s.
Originally, the sterilization program was not scheduled to be fully operational for another two to three years, but the recent developments may prompt calls to accelerate its implementation.
Texas Governor Greg Abbott underscored the economic stakes, pointing out that the state’s agriculture industry—supporting around 2 million jobs and valued at $867 billion—is directly threatened by the parasite.
A 2024 USDA report estimated that a full-scale outbreak in Texas could cost the state over $1.8 billion due to livestock deaths, increased labor demands, and veterinary treatments.
The USDA has noted that screwworms remain endemic in parts of the Caribbean and South America, including Cuba, Haiti, the Dominican Republic, and several South American countries. In July, Mexico reported a confirmed screwworm case in Ixhuatlán de Madero, Veracruz—approximately 370 miles from the Texas border. In response, the Department of Health and Human Services temporarily halted cross-border cattle trade, following earlier suspensions in May and November.
Though human cases of screwworm infestation are rare and typically treatable, they can be fatal if not addressed promptly. The parasite’s larvae—named for their screw-like burrowing motion—emerge from eggs laid in wounds or exposed tissue, causing severe and often gruesome infections.