U.S. officials say a New World screwworm was detected in Mexico roughly 25 miles from the U.S. border, the closest confirmed encounter near U.S. soil since at least last September. The U.S. Department of Agriculture reported the parasitic fly was found Thursday on a 5-year-old goat in Coahuila state, which borders southwestern Texas.
According to the USDA, investigators have documented 32 screwworm cases in Coahuila, 19 of which are currently active. Nationwide in Mexico, authorities have identified at least 26,216 cases, with more than 2,700 remaining active. The USDA issues updates twice weekly on new detections within 400 miles of the United States and emphasizes on its screwworm information page that the pest is not present in the U.S. and that the immediate risk to people, livestock and other animals in the United States is very low.
The parasite has been moving northward in recent years. In April, Texas officials noted a detection about 60 miles from the border, and state agencies have been warning outdoor enthusiasts since late 2024 to be cautious around open wounds. The screwworm has appeared increasingly farther north through Central America and into Mexico over the past three years, according to the Centers for Disease Control and Prevention.
Screwworms are parasitic flies whose larvae feed on living tissue. Adult females lay eggs in open wounds or natural openings such as the eyes, ears, nose and mouth. When the eggs hatch, larvae burrow into and consume flesh, potentially causing severe injury to animals and, rarely, humans.
U.S. health authorities last year confirmed the first New World screwworm case identified in a human in the United States: a traveler who returned to Maryland from El Salvador. Federal and state health officials said the person recovered and investigators found no evidence the infection spread to others or to animals.
Federal and state agencies are monitoring the situation and sharing regular updates. While officials describe the current risk to the U.S. as very low, they advise people who spend time outdoors or handle animals to protect wounds, check livestock regularly, and report suspicious cases to local animal health authorities.
Edited by Melissa Gaffney. Reporting contributions from The Associated Press and Sarah Lynch Baldwin.