New World Screwworm enters the U.S.

NWS infestations were discovered just days apart on calves that grazed
roughly 5.6 miles from each another. (Photo via Hoosier Ag News) 

Despite ongoing efforts from the U.S. Department of Agriculture, the Mexican government and on-the-ground teams along the U.S.-Mexico border, last week the USDA's Animal and Plant Health Inspection Service (APHIS) confirmed two cases of New World screwworm in Texas livestock, reports Jennifer Carrico of Progressive Farmer. In both cases, the flesh-eating blowfly larvae were discovered in young calves about 6 miles apart in Zavala County, Texas.

After the second case was confirmed, Texas Governor Greg Abbott "issued an updated statewide disaster declaration for the NWS infestation," Carrico writes. At a news conference, Abbott encouraged the use of "all state resources to combat the NWS." Additionally, the executive director of the Texas Animal Health Commission, Budd Dinges, reminded the public that NWS isn't a threat to consumer food safety but rather poses a threat to livestock production. 

In response to the infestations, APHIS has "deployed mobile response trailers, and sterile fly releases are underway with 2 million aerially and 4 million released on the ground per week," Farm Journal reports. "Movement control zones have been activated at a 20-kilometer (12.4-mile) radius around each site."

Both NWS cases were found in Zavala, Texas, 
in red above. (Wikipedia map)

The discovery prompted the Canadian Food Inspection Agency to place "temporary restrictions on livestock imports from Texas," reports C.J. Miller of Hoosier Ag Today. "Under the order, cattle, horses and other livestock that originated in Texas or were present in the state within 21 days before entering Canada will be denied entry."

Although the USDA intensified its battle to prevent the NWS from reentering the U.S. including banning Mexican livestock from entering the U.S. beginning in July 2025, some ranchers don't think the government's response was enough.

"On Friday, about 100 ranchers in mud-splattered boots and cowboy hats packed a small high school cafeteria for a Texas Animal Health Commission briefing on screwworm, peppering officials with questions and venting frustration over what they saw ​as a slow federal response,” reports Heather Schlitz of Reuters. 

Even as the USDA works to contain NWS infestations, they are likely to spread throughout the summer months, Miller reports. Prior to last week, the NWS hasn't been found in the U.S. for at least 60 years.

USDA breaks ground on New World Screwworm sterile fly facility in Texas. So far, efforts have kept NWS out of U.S.

The NWS blowfly has not crossed into the U.S.
(USDA photo)

As part of U.S. efforts to keep the aggressive New World Screwworm out of the country, U.S. Department of Agriculture Secretary Brooke Rollins celebrated the groundbreaking of the USDA's domestic sterile fly production facility last week at the Moore Air Base in Edinburg, Texas, reports Jennifer Carrico of Progressive Farmer.

The new facility will add to the USDA's ongoing arsenal aimed at keeping the blowfly and its flesh-eating larvae from entering the U.S. from Mexico and infecting livestock, other warm-blooded wildlife, pets and even humans.

"Rollins said a year ago, the models showed NWS would have moved into the U.S. by now, but it has not and keeping the pest out has been a huge undertaking for all involved," Carrico writes. "Since last July, USDA has monitored over 7,000 fly traps on the border and has collected over 51,000 fly specimens, with all being negative for NWS."

Sigrid Johannes, senior director of government affairs for the National Cattlemen's Beef Association, told reporters, "The facility in south Texas will help give us a high enough inventory of sterile flies to fight NWS and hopefully eradicate it."

As NWS has moved closer to the U.S., with the closest case just 90 miles away, treatment has been top of mind for U.S. livestock producers. 

The flesh-eating larvae are not "a food safety concern, but rather an animal welfare concern. There would also be immediate trade implications for live animals," Carrico explains. The USDA also has a "Screwworm Response Playbook that outlines science-based strategies for officials at the federal, state, and local levels with how to coordinate response operations."