The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service announced on June 4, 2026 [4], that a New World screwworm parasite was found in a calf in Texas.
The discovery is significant because the flesh-eating parasite was eradicated from U.S. livestock in the 1960s [2]. Its return poses a potential threat to the agricultural economy, pets, and local wildlife.
Officials identified the parasite in a three-week-old calf [1] located in Zavala County. The animal was found near the town of La Pryor, which is approximately 62 miles from the U.S.–Mexico border [3].
The New World screwworm is known for invading the living tissue of warm-blooded animals. Because the parasite remains endemic in neighboring Mexico, officials said it likely entered the U.S. from across the border [2].
This detection marks the first case of the parasite in U.S. livestock since the 1960s [2]. The USDA-APHIS is now monitoring the region to prevent further spread of the infestation.
Agricultural experts said that the parasite can cause severe tissue damage and death if left untreated. The proximity of the infection to the border highlights the ongoing challenge of maintaining biological barriers against endemic pests from neighboring regions.
“The parasite was eradicated from U.S. livestock in the 1960s.”
The reappearance of the New World screwworm after six decades suggests a breach in the biological containment strategies that have kept the U.S. livestock industry free from the parasite. Because the parasite is endemic in Mexico, this case indicates a high risk of re-introduction, potentially necessitating an increase in border surveillance and the deployment of sterile insect technique (SIT) to prevent a widespread outbreak.
