A flesh-eating parasitic fly not found in the United States since 1966 has now been confirmed in two states, federal officials announced this week, reigniting concerns about the agricultural threat that devastated American livestock before a landmark binational eradication campaign.
The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) confirmed the first U.S. case of the current outbreak on June 3 in Zavala County, Texas. By June 8, the total had climbed to five: four in Texas — spanning Zavala, La Salle, and Gillespie counties — and one in a dog in Lea County, New Mexico, the first confirmed case in a companion animal and the first case outside Texas.
Cochliomyia hominivorax (Latin: “man-eater”) lays eggs in open wounds of warm-blooded animals; larvae burrow into living tissue, causing severe injury and death if untreated. The United States declared the country free of indigenous screwworms in 1966 following a cooperative sterile-insect program with Mexico in which more than 94 billion sterile flies were released from 1962 to 1975. The pest was subsequently pushed south through Mexico by 1991. The current outbreak has moved northward through Central America and Mexico since late 2024, with Mexico recording more than 28,200 cases since November of that year.
On June 9, Mexico announced the suspension of most live-animal imports from the United States — covering cattle, horses, pigs, sheep, and goats — citing a need to protect screwworm-free northern states. In response, the United States paused planned reopenings of border ports to livestock trade.
The Centers for Disease Control and Prevention classifies human-infestation risk as low; no locally acquired human cases have been reported in the current outbreak. However, any open wound — including scratches, insect bites, or surgical incisions — can attract egg-laying flies in affected counties. Residents and travelers in Zavala, La Salle, Gillespie, and Lea counties should keep wounds cleaned and covered, use insect repellent, and wear long-sleeved clothing outdoors. Healthcare providers who suspect an infestation should report immediately to their state or local health department.