After months of warnings and increased activity in neighboring Mexican states, the New World screwworm (NWS) has been detected in a three-week-old calf in Zavala County, Texas, near the US-Mexico border. So far there is only a single detection, the US Department of Agriculture (USDA) said yesterday.
US Secretary of Agriculture Brooke Rollins confirmed the detection, saying state and federal officials were taking immediate action to control the pest and eliminate it from Texas. The fly had previously been eradicated in the United States in 1966, though erratic outbreaks have occurred as recently as 2016 in the Florida Keys.
The larva (maggot) of the parasitic fly, Cochliomyia hominivorax, poses a significant threat to livestock and pets, and it can rarely infect humans. The parasite enters any warm-blooded animal through an open wound and feeds on the animal’s flesh, and infection is fatal if not treated. NWS maggots were found in the umbilical area of the calf.
Protecting our livestock industry is a national security issue.
“Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” said Dudley Hoskins, the under secretary for marketing and regulatory programs at the USDA, in the agency release. “USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before, and we will do it again.”
Millions of sterile flies to be released
To stop the spread, officials will establish a 20-kilometer (12.4-mile) infested zone around the detection and implement subsequent quarantines, movement controls, and surveillance in that area. Millions of sterile NWS flies will be released in Texas and Mexico in the coming days, and there will be increased trapping at the border. Releasing sterile male flies outside of affected areas ensure that female NWS flies will encounter only sterile partners and not be able to reproduce, as the flies mate only once.
A month ago, the first confirmed detection of New World screwworm in the Mexican state of Coahuila prompted Texas officials to send a warning. “This screwworm detection in Coahuila is a serious wake-up call. New World screwworm has now been found only 119 miles from the Texas border—at roughly the same latitude as Zapata, Texas, and north and west of the Rio Grande Valley,” said Texas Agriculture Commissioner Sid Miller in a statement following the detection.
Since 2024, Mexico has documented a rise in both animal and human cases, especially in Chiapas state. Mexico has confirmed 27,449 cases of screwworm in animals since November 2024, and as many as 2,000 are currently active. As of February this year, 141 people had been infected.
