USDA Urged to Ramp Up Efforts Against New World Screwworm

A bipartisan group of lawmakers, including 25 from Texas, is urging the U.S. Department of Agriculture (USDA) to expand their New World screwworm (NWS) eradication and containment efforts to protect the U.S. cattle industry.

In a letter to U.S. Secretary of Agriculture Brooke Rollins, U.S. Rep. Tony Gonzales (R-TX) said a growing number of NWS cases in Mexico is concerning.

“In November 2024, we first received reports of NWS detected in the Mexican state of Chiapas. The number of reported cases has surged from five to now at least 33 and has spread to the states of Campeche and Tabasco,” Gonzales wrote. “This raises a critical question of how many cases are truly out there and whether we have mechanisms in place to ensure the safety of U.S. livestock and wildlife.”

Screwworms were eradicated from the U.S. in the 1960s. Since then, USDA said there have been a few cases, but not widespread.

If NWS were to become widespread in the U.S. again, USDA Animal and Plant Health Inspection Service (APHIS) officials said it could cost hundreds of millions of dollars in lost animals, treatments and labor.

It could affect U.S. trade, as well.

NWS larvae live off the flesh of living mammals. They burrow into wounds, causing extensive and serious damage, often deadly, to animals.

“Left unchecked, an outbreak could cost livestock producers millions of dollars per year and inflict detrimental economic losses on the national economy,” the letter said.

NWS was successfully eradicated from the U.S. thanks to a sterile fly technique that involves dropping sterile flies out of airplanes over an infected area to disrupt the flies’ reproduction cycle.

The technique was developed in Kerrville.

Gonzales said there are concerns that if NWS is detected in the U.S., there will not be enough sterile flies available to protect livestock and wildlife.

“The current and only accessible sterile fly production facility in Panama, which is operated jointly by USDA and the Panamanian government, is maxed out at producing 100 million sterile flies per week,” the letter said. “This output is no longer sufficient to maintain an effective barrier against NWS migration.”

Gonzales wrote that to successfully push the NWS population back into Central and South America, it is estimated that an additional 100 million sterile flies per week will be needed.

“To address this growing concern across our livestock, farming and wildlife industries, we urge the USDA to work with state, local and relevant industry stakeholders to proactively address this emerging threat—including considering the feasibility of establishing a sterile fly production facility in Texas or the southwest,” the letter said.

The letter is signed by Gonzales and the following representatives from Texas: Monica De La Cruz, Ronny Jackson, Henry Cuellar, Vicente Gonzalez, Sylvia Garcia, Michael Cloud, Marc Veasey, Jasmine Crockett, John Carter, Jake Ellzey, Jodey Arrington, August Pfluger, Morgan Luttrell, Pete Sessions, Keith Self, Craig Goldman, Michael McCaul, Brian Babin, Nathaniel Moran, Troy Nehls, Lance Gooden, Pat Fallon, Dan Crenshaw and Brandon Gill.

“It goes to show that in Texas, lots of members are tracking this issue, and I wanted to put it on paper so that way not only are we tracking it, but we are unified in making sure that we get ahead of any problems,” Gonzales told the Texas Farm Bureau Radio Network.

Gonzales said he believes the letter to USDA was well received.

“I think the new secretary understands Texas really well,” Gonzales said of Rollins, who is from the Lone Star State. “She certainly understands the ag space really well. I think the letter will resonate.”

TFB President Russell Boening thanked Gonzales for leading the letter highlighting the need to be proactive and safeguard against the risk NWS pose to the U.S. livestock and wildlife industries.

“The New World screwworm is a devastating pest that would cripple the United States livestock industry, and an infestation would cause significant losses to livestock and wildlife populations,” Boening said. “Therefore, it’s critical to be vigilant and provide resources to swiftly respond. Farmers and ranchers need assurance that needs will be met since this pest has not been on the mainland United States in many decades.”

NWS was found in a cow in southern Mexico last November at a checkpoint Mexico had set up to protect the country from NWS.

At the time, APHIS officials told the Texas Farm Bureau Radio Network they believed the cow was illegally taken into Mexico from Guatemala.

All imports of cattle from Mexico were temporarily halted to ensure NWS did not enter the United States, and APHIS worked with Mexico to distribute sterile flies in the impacted areas in an effort to contain NWS.

Mexico was also reportedly considering building a sterile fly facility of its own.

Since then, APHIS has reopened the border to cattle from Mexico and has set up check points and a system at the U.S.-Mexico border to evaluate and treat all cattle entering the U.S. for screwworms.

Texas Animal Health Commission (TAHC) is urging people to monitor their animals for screwworms.

Clinical signs include: irritated or depressed behavior, loss of appetite, head shaking, smell of decaying flesh, evidence of fly strike, presence of fly larvae (maggots) in wounds and isolation from other animals or people.

To avoid introduction of NWS, TAHC encourages keeping open wounds clean and covered. People should also treat clothing, gear and people with proper repellents.

Those traveling, especially in NWS-infested areas, should ensure pests and vehicles are inspected for NWS flies and larvae.

Suspected cases of NWS should be reported to your veterinarian or TAHC.