Texas Reports First Screwworm Case in Decades, Raising Livestock Concerns

The United States has confirmed its first domestic case of the New World screwworm in decades after the flesh-eating parasite was detected in a calf in southern Texas, triggering emergency containment efforts and renewed concerns for the nation’s livestock industry.

According to the U.S. Department of Agriculture (USDA), laboratory tests confirmed the presence of the parasite in a three-week-old calf in Zavala County, near the U.S.-Mexico border. The discovery marks the first confirmed infestation in U.S. livestock since the pest was eradicated from the country in 1966 through an extensive sterile-fly eradication program.

The New World screwworm is a parasitic fly whose larvae infest open wounds and feed on the living tissue of warm-blooded animals. If left untreated, infestations can cause severe injuries, infections, and death. Although livestock are most vulnerable, wildlife, pets, and in rare cases humans can also be affected.

Federal officials said the parasite has been steadily advancing northward through Mexico, where tens of thousands of cases have been recorded since late 2024. Just days before the Texas detection, Mexican authorities reported a screwworm case in the border state of Coahuila, only about 25 miles from Texas.

In response, the USDA and Texas animal health authorities have established a quarantine zone around the affected area, restricted the movement of susceptible animals, increased surveillance, and expanded trapping operations. Officials are also deploying sterile male flies, a proven strategy that helped eliminate the pest from the United States more than half a century ago.

While authorities emphasized that the discovery does not pose a threat to the U.S. food supply, agricultural experts warn that a wider outbreak could have major economic consequences. Estimates suggest that an uncontrolled spread could cost Texas’ livestock sector as much as $1.8 billion and disrupt cattle markets across the country.

The infected calf is reportedly receiving treatment, and no additional cases have been confirmed so far. Officials expressed confidence that aggressive containment measures can prevent the parasite from becoming established in the United States once again.