Full Breakdown
Resurgence of New World Screwworm Threatens Livestock and Human Health in North America
8/13/2026, 12:58:59 AM
Reappearance of the Parasite in Mexico and the United States
Researchers analyzing Mexican health data identified a sharp rise in New World screwworm (Cochliomyia hominivorax) infestations after the fly re-established itself in late 2024. Between April 2025 and March 2026, 204 human cases were reported, most on lower limbs, with six deaths and one directly attributed to the parasite. A later Ministry of Health report cites over 500 human cases since the re-emergence. In the United States, the first confirmed infestation was recorded in Texas in June 2025; as of August 9, 45 animal cases had been confirmed in Texas and New Mexico, with no locally acquired human cases.
Historical Context and the Broken Barrier
For decades, a coordinated sterile-insect technique (SIT) program created a biological barrier that stopped the fly’s range at Panama. Mexico was declared free of screwworm in 2003 and Panama in 2006. The barrier collapsed after 2022, allowing the parasite to move northward, re-appearing in Mexican livestock in late 2024 and reaching the United States three years later.
Key Data and Economic Stakes
- Human cases (Mexico): 204 confirmed (April 2025 – March 2026) vs. > 500 reported later.
- Human deaths: Six, with one directly caused by screwworm myiasis.
- Animal cases (U.S.): 45 confirmed in Texas and New Mexico as of August 9.
- Animal cases (Mexico): More than 36,000 reported by early August 2026, with nearly 2,000 active.
- Economic risk: USDA estimates the Texas outbreak could threaten up to $1 billion in livestock losses.
- Sterile-fly production: Panama facility outputs ~100 million sterile males weekly; the Texas plant is slated for 100 million per week by end 2027 and up to 300 million by late 2028.
Official Statements and Federal Response
The USDA and DHS signed a Memorandum of Understanding to coordinate surveillance, information sharing, and rapid response. USDA’s New World Screwworm Rapid Response X account announced the Texas sterile-fly facility at Moore Air Base will open spring 2027, seven months ahead of schedule, providing a domestic source of sterile insects.
USDA also launched an expanded drone-surveillance program. Since June 3 2026, more than 1,000 drone flights have surveyed over 20,000 animals in Texas, using high-resolution and thermal sensors to locate wounds that could harbor larvae. On June 18, APHIS teams used drones near Junction, Texas, to map livestock, water sources, and fence lines, then alerted landowners for ground-team follow-up. DHS contributes border-surveillance assets and trains CBP personnel to recognize screwworm signs.
Conflicting Reports and Information Gaps
The discrepancy between the 204 confirmed human cases (April 2025 – March 2026) and the later claim of over 500 cases highlights a gap in publicly available surveillance data. Neither source provides a breakdown of the additional cases, nor does any outlet report confirmed human infections in the United States, leaving the true scope of the public-health threat uncertain.
Upcoming Milestones
- Spring 2027: Opening of the Texas sterile-fly production facility.
- End 2027: Facility reaches 100 million sterile flies per week.
- Late 2028: Capacity expands to up to 300 million sterile flies weekly.
- Ongoing drone surveillance and trap monitoring continue throughout 2026-2028, with monthly audits of Mexican response and coordinated border-state actions.
