The Centers for Disease Control and Prevention (CDC) has confirmed the first human infection with the New World screwworm in the US in decades, after a Maryland patient tested positive earlier this month. Officials said the patient was treated and emphasized that the public risk remains very low.
Maryland health officials reported that the patient received wound disinfection, and the larvae were manually removed. Federal and state agencies have worked together to contain the case and monitor for any potential spread.
Andrew G. Nixon, spokesperson for the US Department of Health and Human Services, said: "The public health risk in the US from this outbreak is very low."
The infection was confirmed on August 4, and details were shared with agriculture and livestock industry leaders on August 20.
Rare but dangerous
The New World screwworm fly (Cochliomyia hominivorax) lays its eggs in the wounds of warm-blooded animals, including cattle and humans. The larvae burrow into living flesh in a screw-like motion, causing painful infections that can be fatal if left untreated.
Although human cases are extremely rare, the parasite has been spreading northward through Central America since 2023. Mexico confirmed a case in July, located approximately 370 miles from the US border.
Livestock concerns
Ranchers and veterinarians have warned that the screwworm could devastate US cattle herds if it crosses the border. Analysts estimate that an uncontrolled outbreak could cost Texas alone $1.8 billion in livestock deaths, treatment costs, and lost productivity.
The US currently imports more than one million cattle annually from Mexico, even as the national herd reaches its smallest size in seven decades.
In an effort to prevent further spread, the US Department of Agriculture (USDA) announced a $750 million program to expand the production of sterile flies. This technique, which involves releasing sterilized males that mate but produce no offspring, was used to eradicate the screwworm in the US during the 1960s.
Until a new facility in Texas becomes operational, the US is relying on a plant in Panama that produces about 100 million sterile flies each week. Experts say five times that number is necessary to prevent the outbreak from advancing north.