WASHINGTON, D.C. — New World screwworm (NWS), a parasitic, flesh-eating insect last seen in the U.S. in 1966, has been confirmed in a calf in Zavala County, Texas, U.S. Ag Secretary Brooke Rollins announced during a hastily called June 4 news tele-conference. 

‘We have a confirmed positive detection of NWS in a three-week-old calf in LaPryor, Texas. USDA and Texas officials have taken immediate action to contain and eradicate in South Texas,” said Rollins. “We have a unified incident command team with the Texas Animal Health Commission (TAHC) and have deployed APHIS (USDA’s Animal and Plant Health Inspection Service) as of yesterday immediately down to the area. We have established a 20-kilometer control area or zone around the detection and have implemented quarantines and movement controls in the area.”

In addition, USDA is expediting the targeted release of “millions” of additional sterile flies in addition to ongoing releases in an effort to disrupt breeding, according to Rollins. “We’re increasing trapping and surveillance for NWS flies along the border just outside of the dispersed area,” she said. “The release of the sterile flies is how we beat this back.”

NWS surveillance in wildlife is likewise being increased, with a “couple of possibilities” of cases eliminated by APHIS in the hours prior to the news conference, Rollins added. In addition, all domestic pets and service animals entering the U.S. through Customs will be inspected for screwworms by the USDA’s “beagle brigade.”

Rollins said the confirmation of a single case of NWS should not be interpreted as indicative of a looming outbreak. “What happened was something that was never supposed to happen again, and that was the breaching of (Central America’s) Darien Gap. But as it began to move up a couple of years ago, the models said that no matter what we did the NWS would be here by summer or early fall,” she said. 

“If we all work together and follow these treatment and movement restriction guidelines there is no reason to believe that this incursion will result in any kind of establishment of the pest on our side of the border, which is different from when it hit us in the 1950s and 1960s.”

An on-site veterinary inspection of the LaPryor ranch where the confirmation occurred revealed no further evidence of NWS in other livestock, according to Texas State Veterinarian Lewis “Bud” Dinges of the TAHC. “There is no evidence of recent movement of other animals onto or off of that premises,” said Dinges. “Our responders are already in the area conducting site visits and evaluating the situation to ensure we have the correct information we need to mitigate the spread.” 

Because NWS travels with livestock movements, the TAHC announced an executive order placing a quarantine on “all warm-blooded animals in the infested zone in the Zavala County area.” The order can be read at bit.ly/NWS-EDO6-3-2

NWS is described as a parasitic fly whose larvae burrow through living flesh and can kill an animal — and even a human — if left untreated. There have been 2,075 confirmed human cases of NWS in Central America and Mexico according to Paul Cantey of the Center for Disease Control. Ten of those cases resulted in death. 

The NWS does not present a food security issue, Rollins stressed. “This is not a disease, it is not a virus, it is simply an insect that lands in a wound and lays eggs that like to eat the flesh around the wound. There is no food safety issue here at all. Once that larva is removed and the wound is cleaned, animals treated early enough will survive and recover,” she said.

A laboratory located on the U.S. side of the Mexican border that will be capable of producing up to 300 million flies per week will not be online until the fall of 2027, Rollins said.

Find USDA updates on the movement of NWS on screwworm.gov.