USDA reports three new cases of screwworm, bringing total to 15

The number of U.S. cases of New World screwworm has risen to 15 after three more animals tested positive in Texas, the Department of Agriculture said in a post on social media on Sunday. 

The USDA announcement comes nearly three weeks after the first domestic screwworm infestation ​in six decades was found in a Texas calf. 

New World screwworm is a parasitic fly that eats warm-blooded animals alive and can infect livestock, pets, wildlife and, in rare cases, people. The larvae burrow into the living tissue of animals and cause severe wounds that can eventually kill, leading to signficant economic losses for ranchers. 

The USDA said it will continue aggressive eradication efforts in affected areas, including the dispersal of tens of millions of sterile flies that halt screwworm reproduction. 

One lamb in Crockett County and two calves in Edwards County, Texas tested positive for screwworm in the past 24 hours, according to the USDA's Sunday evening post on X. 

Texas ranchers have been bracing for screwworm to cross into the U.S. for the past ​year, as the pest advanced north in Mexico. Experts have predicted that a widespread outbreak could cost the ​state $1.8 billion in economic damage and devastate wildlife.

The USDA broke ground in April on a facility to produce sterile flies, which experts describe as the best tool for combating the pest, ​but it will not come online until late 2027.