With threat of widespread outbreak, New World Screwworm cases confirmed within Texas
With the New World Screwworm moving within the Texas border, increased vigilance on herds and wildlife is paramount. NWS flies lay eggs in open wounds or orifices of live tissue. Left untreated, the flesh-eating maggots of the NWS fly can cause death in animals within one week of infestation.
A widespread outbreak could devastate Texas ranchers, wildlife populations, companion animals, and the broader agricultural economy. Texans are increasingly worried regarding the federal response to stop the flies’ northern migration, especially since the first case was confirmed in a three-week-old calf with an umbilical lesion in Zavala County June 3.
The case was confirmed by the National Veterinary Services Laboratory and reported to the Texas Animal Health Commission. On June 5, a second case was confirmed in a 30-day-old calf also in Zavala County, located within the existing infested zone.
And then on June 8, two new cases in a calf and a dog (initially from New Mexico) were found hundreds of miles apart in La Salle and Andrews counties. Federal officials are also investigating additional reports of infected livestock, including confirmed infestation in a goat in Gillespie County. That brings the total number of confirmed cases in Texas to five.
Animal health officials are actively working the case and continuing to expand fly trapping and surveillance efforts to identify additional flies in the area. Late May, the closest confirmed case was roughly 25 miles from the border in a five-year-old goat in Coahuila, Mexico.
Texas Agriculture Commissioner Sid Miller responded this first case in Texas, criticizing the United States Department of Agriculture for what he called a slow, bureaucratic, and incomplete response, and calling on the president to take decisive control.
“For months, the screwworm has advanced rapidly through Mexico in spite of the USDA’s existing gameplan,” Miller said. “Even though billions of sterile flies have been dispersed by USDA, the screwworm has still advanced over 1100 miles from southern Mexico to Texas, and USDA has missed an important component. Now that it appears the first screwworm has arrived in Texas, the consequences of that decision are now staring us in the face.”
To prevent further spread of NWS, TAHC has issued an executive director order that places a quarantine on all warm-blooded animals in the identified infested zone in the Zavala and Uvalde County area, surrounding La Pryor. There are concerns that feral hog, which are plentiful along the border with Mexico, will contribute to the spread, as would the whitetail deer populations.
TAHC is working in coordination with the USDA to expand fly trapping and surveillance efforts to identify any additional flies in the area and investigate potential suspect cases in animals. Epidemiological efforts are underway to learn more about this case and prevent spread of the pest.
According to the USDA, the U.S. food supply is safe at this time. USDA’s Food Safety and Inspection Service ensures that the nation’s commercial supply of meat, poultry, and egg products is safe and properly labeled. NWS do not infest meat, fruits, vegetables, or other food sources.
The U.S. Department of Agriculture authorities in Mexico confirmed 11 new cases of New World screwworm within 100 miles of the U.S.-Mexico border at the end of last month.
The USDA and the Texas Department of Agriculture stated the NWS that “the current risk to livestock, other animals, and people in the United States remains very low.”
Livestock and pet owners can help avoid infestations of NWS by staying vigilant, monitoring animals, especially those with open wounds, and reporting any suspicions of NWS flies, maggots, larvae, and secondary infections. Open wounds should be cleaned and covered straight away.
Prevention is key. Keep open wounds clean and covered and establish effective preventative treatments. When traveling, especially in NWS-infested areas, ensure pets and vehicles are inspected for NWS flies and larvae.
As of June 1, there were roughly 1,800 active cases in Mexico, bringing the total to more than 26,700 since Nov. 2024.
In 2025, U.S. Agriculture Secretary Brooke L. Rollins initiated a multi-pronged, international campaign to keep the parasite outside the United States. A main pillar is sterile fly dispersal from upgrades and newly constructed facilities – releasing sterilized male flies halts the NWS’s reproduction cycle.
In 1966, NWS was eradicated from the United States using the sterile fly method. The new construction of a sterile fly production facility at Moore Air Base in Edinburg targets an initial operational milestone isn’t until Nov. 2027. At that time, it will begin producing 100 million sterile flies per week before ramping up to its ultimate capacity of 300 million flies per week.
Rollins leveraged trade restrictions and securing cooperation agreements to force uninhibited access for USDA aircraft and eradication equipment in Mexico, and maintained stringent animal movement controls and suspensions on live cattle, bison, and equine imports originating from Mexico to secure the border. Additionally, the federal Food and Drug Administration authorized the emergency use of over-the-counter Ivermectin to treat livestock and domestic animals against potential NWS infestations.
With confirmation of these new cases, Texas Governor Greg Abbott has directed the Texas Division of Emergency Management to activate the State Emergency Operations Center at Level II, or Escalated Response, as Texas intensifies efforts to prevent the spread of deadly parasite.
On Jan. 29, Abbott issued a statewide disaster proclamation for all counties in Texas due to the threat NWS poses to the state’s livestock industry, economy, and the potential for widespread and severe property damage for Texas. Abbot has renewed the proclamation each month since.
“We’ve seen detections in four counties and two states,” Texas Department of Agriculture Commissioner Sid Miller said in a press release Monday. “This should set off alarm bells across the country. Every day we delay gives this pest another opportunity to spread.”
Miller urges the President to direct USDA to immediately deploy the Screwworm Adult Suppression System, a proven technology developed by USDA scientists and successfully used during previous eradication campaigns. SWASS uses attractants, bait, and targeted, EPA-approved insecticides to dramatically reduce adult screwworm populations, allowing sterile fly releases to finish the job.
Miller stressed that sterile fly releases remain critical but argued that sterile flies and SWASS are most effective when used together.
“SWASS was developed by USDA, tested by USDA, and successfully deployed by USDA to eradicate screwworm in Mexico and Texas when it last appeared,” Miller said. “USDA already owns the playbook; the only question is whether USDA will use it before this situation gets worse.
“I personally provided research and the SWASS bait formula to Secretary Rollins and her team on three separate occasions while the screwworm continued its northward trek to Texas. Instead of using every available tool, USDA moved too slowly and relied solely on a partial solution that takes years to fully implement.”
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