Darién Gap
Roadless Forest region on the Panama-Colombia border.
The sterile-fly barrier at the Darién Gap held New World screwworm out of Central America until its breach in 2023; by 18 September 2026 Mexico had recorded 575 human cases that year, five times the 2025 total.
Last refreshed: 4 October 2026
Timeline for Darién Gap
Mentioned in: Screwworm cases in Mexico rise fivefold
Pandemics and BiosecurityBackground
The Darién Gap is roughly 106 km of roadless rainforest between Yaviza in Panama and Turbo in Colombia, where the PAN-American Highway is interrupted. More than 520,000 migrants crossed it in 2023 and about 300,000 in 2024.
It was also where the Americas held back New World screwworm. After the United States eradicated the parasite in the 1960s and Mexico was declared free in 1991, a sterile-fly barrier zone was pushed south to the gap from 2006. COPEG, the Panama-US screwworm Commission, says Panama was the biological barrier until June 2023, and it stopped dispersing sterile flies there in May 2024. The breach in 2023, helped by illegal cattle movements north through Central America, opened the parasite's current spread.
The cost now shows up FAR to the north. Mexican health data show four screwworm deaths this year and a fivefold rise in human infestations on 2025. Restoring a barrier depends on sterile-fly supply. Until June 2026, when Mexico opened a plant at Metapa in Chiapas, COPEG's facility near Panama City produced all of the region's sterile flies.