New World screwworm found 25 miles from U.S. border in Mexico

The U.S. Department of Agriculture reported a New World screwworm in a 5-year-old goat in Mexico's Coahuila state on Thursday. The location sits 25 miles from the U.S. border, the closest detection since at least last September. U.S. officials have recorded 32 cases of the parasitic fly in Coahuila, including 19 active cases.

Across Mexico, at least 26,216 cases have been identified, with more than 2,700 remaining active.

Background on the parasite The New World screwworm is a parasitic fly whose larvae feed on living tissue of warm-blooded animals and humans. It typically occurs in South America and parts of the Caribbean but has moved farther north in recent years.

The department updates case data twice weekly for detections within 400 miles of the U.S. border. Its dedicated webpage states the pest "is not currently present" in the United States and the risk to livestock, other animals, and people remains very low.

Prior detections In April, the screwworm was found at a site 60 miles from the U.S. border. Texas officials issued an advisory to outdoor enthusiasts in late 2024 after a case appeared in southern Mexico. Last year, the first human case in the U.S. was confirmed in a traveler who returned to Maryland from El Salvador.

Maryland health officials later said the person recovered and no transmission occurred.