USDA: New World Screwworm Not Yet in the U.S., But Threat Draws Closer

In response, USDA and Texas authorities have launched an aggressive prevention strategy centered on surveillance, movement controls, sterile-fly releases, border inspections, and rapid-response plans designed to contain any potential outbreak before it can establish itself.

This is a reminder that good stewardship often means acting before disaster arrives rather than after. The screwworm is not merely a livestock problem—it threatens wildlife, rural economies, and the people whose livelihoods depend on healthy animals. The encouraging news is that officials appear united around a proven strategy; the challenge now is maintaining vigilance while the pest remains just beyond our doorstep.

NOTE: this article was sent by email to us via Livestock Weekly on Wednesday, June 3rd. It may be out of date.

Despite unverified claims circulating on social media, the New World screwworm (NWS) has not been detected in the United States. However, it is now significantly closer to the border than it was just two weeks ago.

That was the message Secretary of Agriculture Brooke Rollins delivered during a special virtual media briefing held yesterday.

Late last week, Mexico confirmed eight new cases of NWS in the state of Coahuila. The closest case—a five-year-old goat, initially reported as a sheep—was detected just 25 miles from the U.S.-Mexico border.

Rollins told reporters that USDA has been preparing for a potential border breach for more than a year and already has a five-pronged action plan in place focused on:

• Detection
• Containment
• Eradication
• Preparedness
• Sterile fly production

“If the southern border of America is breached, we are preparing to implement the plan the very moment the fly makes it into our country,” Rollins said.

“If we have a domestic detection, USDA and relevant state animal health officials will immediately put in place quarantines and movement restrictions to limit the pest's spread. We will initiate additional trapping and surveillance in the immediate area. We will release sterile New World screwworm flies to eliminate any reproducing populations. The response will be scientifically tailored to the specific incident.”

“We are ready, and we will communicate every step of the process with the public,” she added.

Risk Remains Low for Humans

Rollins emphasized that NWS is a parasitic fly larva capable of infesting livestock, pets, wildlife, and, in very rare cases, humans.

“To be clear, the current risk to public health in the U.S. is extremely low,” Rollins said. “The real risk is obviously to our livestock and our wildlife population.”

As part of the response effort, detector dogs have been deployed at all legal border crossings, and tick rider patrols along the border have been expanded.

Rollins also highlighted new facilities, management tools, prevention strategies, and public outreach efforts underway to prepare for any potential spread into the United States.

“The scale and technological prowess of our response to NWS have been unprecedented,” she said. “We have done everything we can possibly do on our side of the border to keep it out.”

However, Rollins expressed concern over Mexico’s response.

“Mexico has failed to lock down cattle movement in infected zones, and they have failed to check their fly traps daily,” she said.

“We do have a USDA team on the ground in Mexico trying to alleviate that. We have since last year, but it continues to be a problem.”

USDA plans to provide media updates twice weekly going forward.

Rollins also pointed citizens to screwworm.gov, which provides the latest information on confirmed cases, locations, affected species, and age data. USDA has also established a dedicated email address—screwworm@usda.gov—which is monitored 24 hours a day, seven days a week for public questions and concerns.

Current Situation in Mexico

Rear Admiral Michael Schmoyer, Associate Administrator for APHIS and Director of the New World Screwworm Directorate, reiterated that NWS is not currently present in the United States.

According to Schmoyer:

• Approximately 1,882 active cases currently exist.
• More than 26,754 total cases have been recorded since the response began in November 2024.

While cases have increased within 100 miles of the U.S. border, all of those detections remain inside the sterile-fly dispersal zone.

When asked how the pest is spreading, Schmoyer noted that data published on screwworm.gov indicates the majority of cases are associated with animal movement.

Texas Officials Say State Is Ready

Texas State Veterinarian and Executive Director of the Texas Animal Health Commission (TAHC), Dr. Bud Dinges, reminded participants that NWS is not an infectious disease.

“It is an ectoparasite,” Dinges said.

“We’ve dealt with the cattle fever tick in this state for over 100 years, and we understand how to deal with an ectoparasite. We understand the importance of movement controls, inspections, and treatments to prevent the spread of such a pest throughout the rest of the nation.”

Dinges said TAHC has spent the last two years developing an NWS-specific response plan, coordinating outreach efforts, and training personnel.

“We are prepared to respond to New World screwworms immediately,” he said.

“Texas Animal Health Commission continues to work with our partners at all levels of government, across all sectors of the animal agriculture industry, with veterinarians and animal owners, to ensure preparedness and that our efforts are methodically efficient and coordinated.”

TAHC is also increasing personnel in South Texas to expand outreach and public awareness efforts.

“TAHC personnel are not responding to a detection of New World screwworm in Texas or the United States,” Dinges emphasized.

“As a precaution, USDA and TAHC staff are leveraging and expanding existing ground release sites for the distribution of sterile flies in South Texas near the Texas-Coahuila border.”

He explained that aerial dispersal grids and surveillance trap locations are continuously adjusted based on scientific assessments to maximize the effectiveness of sterile-fly releases and detection efforts.

What Animal Owners Should Do

Dinges urged livestock owners and pet owners to remain vigilant.

“Monitor animals closely and as often as possible for wounds and suspicious larvae,” he said.

Any suspected infestation should be reported immediately to a local veterinarian and/or the Texas Animal Health Commission.

“Quick notification leads to quick detection, and a quick response is what will stop this pest from spreading,” Dinges said.

Animal owners should also promptly treat and cover wounds.

“That is what the fly is attracted to,” he reminded.

Finally, Dinges stressed the importance of maintaining an active veterinarian-client-patient relationship.

“Stay vigilant and stay aware. From government agencies to individual animal owners to veterinarians to the great agriculture industries of Texas and beyond, it is going to take all of us to prevent the spread of New World screwworm.”