[REVISION HISTORY]

US-Mexico screwworm outbreak: containment and human impact

Updated 20 times since CLSTR started tracking revisions of this situation.

What changed

2026-09-15 21:42 UTC → 2026-09-18 15:14 UTC · added ~~removed~~

The New World screwworm outbreak continues to impact the U.S.–Mexico border, with containment efforts facing new biosecurity challenges. While the USDA-APHIS has lifted the infested zone in New Mexico following a single confirmed case in a dog on 7 June 2026, the parasite remains a threat near the border. The resurgence, which began in 2023, has resulted in over 144,000 animal cases and 1,100 human cases across the region. In ~~Mexico, Senasica reports~~ the United States, a ~~national total of 2,011 cases, including 845 in cattle and 769 in dogs. In Coahuila, 38 confirmed cases have~~ second case has been ~~reported across various species, including cattle, dogs, horses, pigs, sheep, and goats. Local officials~~ confirmed in ~~Monclova have noted that many treatments applied~~ a horse in ~~June and July are “losing their effectiveness,” necessitating urgent renewed medication applications by Senasica and regional livestock unions.~~ Grant County, New ~~activity~~ Mexico. Despite this, U.S. Agriculture Secretary Brooke Rollins announced that the Santa Teresa port is scheduled to reopen for Mexican cattle imports on 24 September, following a closure of over a year. The USDA has ~~been reported~~ invested over $1.3 billion in ~~Sonora, where Senasica recorded 55 active~~ containment, including drone monitoring and the release of more than one billion sterile flies. In Mexico, livestock management remains critical. Sonora reports approximately 59 cases across ~~nine~~ 11 municipalities, including Hermosillo, with ~~the highest concentrations in Álamos and Huatabampo. Control strategies there include movement restrictions and sterile fly~~ weekly releases ~~to protect cattle exports to the United States.~~ of over 12 million sterile flies. In the State of Mexico, ~~authorities reported 19 active cases concentrated in the southern region. To combat the spread, officials have implemented~~ biological trapping ~~barriers, a strategy that has reportedly “prevented the birth of approximately~~ barriers have prevented an estimated 29 million ~~larvae.” Human impact remains severe. Mexico has recorded four deaths~~ larvae from hatching. Tamaulipas reports 24 active cases, while cattle exports from Coahuila to the ~~parasite in 2026,~~ U.S. may face delays of up to four months due to sanitary protocols. Human impact persists, with ~~the latest fatality in~~ Veracruz ~~during the week of 16–22 August. Since~~ reporting the ~~start~~ highest number of ~~2026,~~ human cases in Mexico ~~has~~ for 2026, totaling 113 confirmed ~~516~~ cases as of 11 September—roughly 20 percent of the 564 national cases. Veracruz has also recorded one death. Other states with significant human ~~cases, totaling 633 since 2025.~~ cases include Chiapas, Oaxaca, Puebla, Yucatán, Guerrero, and San Luis Potosí.

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