Mexico Confirms Second Screwworm Case in Two Days as Outbreak Persists

Mexican agricultural authorities reported on Jan. 2 that a goat in the State of Mexico tested positive for New World screwworm and received treatment, marking the second confirmed detection in two days. The announcement followed a Dec. 31, 2025 finding of the parasite in a six-day-old calf in Tamaulipas. Authorities said both animals were treated and were the only positives at their respective locations.

At the goat's site, officials tested 20 other animals, all of which returned negative results and were given preventive treatment. Regional authorities launched active surveillance and preventive measures at nearby farms and ranches, stepping up sanitary alerts and livestock controls to contain further spread.

New World screwworm is a parasitic fly whose larvae develop in wounds, burrowing through animal flesh and, if untreated, potentially killing the host. The pest had been eradicated from much of North America before its recent resurgence. Government reporting notes the outbreak has advanced northward from Central America into southern and then more central and northern Mexican states, taking advantage of climates that favor the fly's life cycle.

Through Dec. 31, 2025, Mexican government data show a cumulative total of 13,106 screwworm cases since November 2024, with 671 active cases on record. The most affected states by confirmed case totals are Chiapas, followed by Oaxaca, Veracruz and Yucatan, all regions with climates conducive to the pest.

Control efforts have relied on testing all animals at sites of detection, treating positives, and administering preventive treatments to exposed livestock. Authorities have also declared heightened sanitary alerts and intensified active surveillance on farms and ranches in affected areas. Officials say binational coordination is under way with neighboring countries to limit cross-border spread, reflecting the pest's capacity to travel with livestock movements and wild animal hosts.

The outbreak has also had immediate trade and market consequences. The United States has kept its southern border largely closed to Mexican livestock since May, and the discovery of additional cases is expected to delay any reopening of the border to Mexican feeder-cattle imports. Market observers reported rapid price moves after the Jan. 2 announcement: February live cattle rose $4.40 to close at $236, a weekly gain of $6.35, and March feeder contracts jumped $7.625 to $352.95.

Veterinarians and livestock growers face a race to maintain containment while minimizing economic damage. The combination of active infections, preventive campaigns and border restrictions underscores the challenge of eradicating a pest that can multiply rapidly in warm, humid conditions. With the outbreak still active across multiple states, authorities cautioned that continued surveillance, quick treatment of any new detections and coordinated regional action will be essential to preventing further spread and restoring trade confidence.