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First US screwworm detection in six decades sparks response
Federal and state officials have launched a containment strategy after larvae of the New World screwworm were found in a Texas calf, marking the first US case since 1966. The parasitic fly poses a severe threat to livestock, though human risk remains low.
Containment efforts focus on sterile insect technique
Agriculture authorities are releasing millions of genetically altered sterile flies in a bid to disrupt the screwworm population. Females mate only once, so sterile males prevent viable offspring. However, production capacity falls far short of the 600 million flies per week experts say are needed to curb the outbreak.
Current facilities in the US and Mexico can produce just 100 million sterile flies weekly. Since the infected calf was discovered in La Pryor, Texas-30 miles from the Mexican border-officials have released 8 million sterile flies by ground and air.
Quarantine zone and border surveillance expanded
The USDA has established a 20-kilometer control zone around La Pryor, enforcing quarantines, movement restrictions, and heightened surveillance. Sniffer dogs from the "Beagle Brigade" are now stationed at border crossings to detect infested livestock or pets.
Officials warn that human transport of animals remains the primary long-distance spread vector. While the flies can travel short distances, most US cases since 1966 have involved travelers returning from Latin America.
Ranchers criticize federal response as inadequate
Cattle producers in Texas have condemned the federal government's delayed action, citing budget cuts to international monitoring programs under the previous administration. Texas Agriculture Commissioner Sid Miller accused officials of a "slow, bureaucratic" response that allowed the pest to advance unchecked through Mexico.
USDA Secretary Brooke Rollins attributed the northward spread to "open border policies" and cartel smuggling, while also criticizing Mexico's containment efforts as insufficient. Democrats, meanwhile, blamed the Trump administration's 2019 elimination of USAID's screwworm tracking program for the delayed response.
Climate change and historical outbreaks fuel concerns
The screwworm, native to tropical regions, thrives in warmer climates but may expand northward due to rising temperatures. The last major threat to US cattle occurred in the 1970s, when sterile fly releases pushed the pest south of Panama's Darien Gap. However, cases surged across Central America in 2022, reaching Mexico by 2024.
The CDC reports 2,070 human cases in the current outbreak, though fatalities are rare if treated promptly. Livestock, however, face severe risks: larvae burrow into open wounds or mucous membranes, consuming living tissue and often killing untreated hosts.
Preventive measures urged for ranchers and public
Officials advise ranchers to cover livestock wounds to prevent infestation and to report suspected cases immediately. The public is encouraged to inspect pets and themselves for signs of screwworm larvae, particularly after travel to affected regions.
"There is no reason to believe this incursion will establish the pest in the US," Rollins said. "But vigilance is critical."
USDA Secretary Brooke Rollins
