New World screwworm

New World screwworm larvae feed on living tissue. The female fly lays eggs in an open wound, and the larvae that hatch eat into the flesh. The parasite mainly attacks livestock, but any untreated wound, on an animal or a person, can host it, so human cases rise with the number of flies in the field.

Mexico's health ministry, the Secretaría de Salud, tracks human cases through a special surveillance system for screwworm myiasis. Its 2026 count had reached 575 by 18 September, roughly five times the 117 cases of the whole of 2025, El Universal reported. Since April 2025 the parasite has infested 692 people in 27 states.

Four people have died, all in 2026, in Oaxaca, Querétaro, Veracruz and Yucatán. Chiapas, on the border with Guatemala, has the most human cases, at 165, which places the heaviest burden on the route by which the fly has moved north.