The flesh-eating New World screwworm has been confirmed in a Texas calf — the first detection of the parasite in U.S. livestock in decades.
The Department of Agriculture announced Wednesday that a three-week-old calf in Zavala County, Texas, tested positive for New World screwworm, a parasite whose larvae feed on the living tissues of warm-blooded animals.
The screwworm infestation was found in the calf’s umbilical area. The parasite typically enters animals through open wounds, where larvae burrow into the flesh and feed on living tissue.
“All models showed New World screwworm entering the country in 2025; however, thanks to the hard work across the entire Trump administration and our industry, state, and local partners, we were able to buy time for this moment.”
Dudley Hoskins, Under Secretary for Marketing and Regulatory Programs, said protecting America’s livestock is a national security issue “of the utmost importance.”
“USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico,” Hoskins said. “The United States has defeated this pest before, and we will do it again.”
The U.S. case comes after the screwworm was found last week in a five-year-old goat in Coahuila, the Mexican state that borders southwestern Texas. A separate case was reported Sunday in a dog in Tamaulipas, another bordering Mexican state.
The current outbreak in Mexico prompted Secretary of Agriculture Brooke Rollins to shut down livestock trade across the southern border in May 2025. There was one confirmed U.S. case last year from a person who returned to Maryland after traveling to El Salvador.
Federal officials said no additional cases have been identified in the United States. The USDA noted the food supply is safe because screwworms do not infest meat, fruits, vegetables, or other food sources.
The USDA reports that screwworm maggots cause painful, foul-smelling wounds — and that maggots can sometimes be seen or felt in open wounds or in body openings, including the nose, mouth, eyes, ears, and genitals.
If the infestation isn’t caught early and treated quickly, it can lead to extensive tissue damage and sometimes death.
Adult screwworm flies are the size of a housefly, with orange eyes, a metallic blue or green body, and three dark stripes along their backs. The parasite is typically found in South America and parts of the Caribbean, but has been found farther north in Central America and Mexico over the last three years.
The USDA warns that if you see signs of maggot infestations in live or very recently dead wild animals, especially near the U.S.-Mexico border, call 866-487-3297 or report it to your local USDA Wildlife Services office.
