New World screwworm confirmed in Texas dog as US case count rises to four

Today, the US Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed NWS in a calf in La Salle County and a dog in Andrews County. The new cases extend the parasite's known reach beyond the initial detections in Zavala County.

According to the USDA, a veterinarian in Andrews County submitted the samples from the infested dog. Epidemiological investigations for both cases remain ongoing.¹

"Over the past week, USDA has identified and expeditiously confronted four confirmed detections of New World screwworm," Dudley Hoskins, USDA under secretary for Marketing and Regulatory Programs, said in a USDA announcement.¹ "We need the partnership of animal owners across the region—please stay vigilant, check your animals closely, and report anything that looks suspicious."

The growing case count comes as parasitologists warn that confirmed detections may represent only a fraction of the true number of infestations. Christopher Lee, DVM, MPH, DACVPM, DACVM (Parasitology), assistant professor of microbiology at Lincoln Memorial University's Orange Park College of Veterinary Medicine in Orange Park, Florida, told dvm360 last week that the single confirmed case at the time likely represented only part of the picture. "The likelihood is that we have potentially hundreds to thousands of these flies here already," he said.

Kathryn E. Reif, PhD, MSPH, associate professor in the department of pathobiology at Auburn University's College of Veterinary Medicine, said the initial detection was not unexpected. "We knew it was a when and not an if," Reif said in a statement provided to dvm360.

NWS has spread through Panama, Central America, and Mexico over the past several years. "This is not going to be an isolated incident," Lee said. "This is the early stages of reestablishment."

The first US detection in nearly 60 years was confirmed June 3 in a 3-week-old calf in Zavala County, with larvae found in the umbilical area. A second Zavala County case followed June 5, located 5.6 miles from the initial detection.²

The June 8 detection in a calf in neighboring La Salle County expands the area in which the parasite has been identified, with the county located roughly 80 miles from the initial Zavala County cases.

Andrews County, where the infested dog was identified, lies nearly 400 miles northwest of Zavala County, though early reports indicate the dog had recently been in Mexico.

Veterinarians at the frontline: What to watch for and what to do if case is suspected

Reif urged veterinarians, livestock owners, and pet owners to remain vigilant but avoid panic. "[NWS] is an important and serious animal health concern, but early detection, rapid reporting, and a coordinated management response are how we prevent spread," she said.

She advised animal owners and clinicians to check animals carefully, paying particular attention to the navel area of newborns, tick bites, surgical sites, injuries, and any wounds that appear to be worsening, draining, painful, or infested with larvae.

"If you do see larvae or maggots in a wound, or suspect [NWS] infestation, please contact your veterinarian, state animal health official, or USDA APHIS right away," Reif emphasized.

Larval specimens preserved in alcohol—at least 10 maggots when possible—should be submitted to the National Veterinary Services Laboratories for confirmatory identification. A cigar-shaped maggot with prominent hooks at the pointed end and two dark pigmented tracheal trunks visible at the blunt end warrants immediate submission, as these features are telltale signs of NWS. "If you have maggots and you're concerned, send as many as you can to your lab," Lee said.

Dogs and cats are at risk, but isoxazoline-based combination parasite prevention offers protection. Lee urges veterinarians to reinforce consistent, monthly use of those products with clients.

Reif also emphasized proactive prevention measures, including routine parasite control, prompt wound care, and management practices that reduce opportunities for infestation.

Economic stakes and food safety

Beyond animal welfare, livestock producers in affected regions could be drastically impacted. The detections come as the US cattle herd remains at its lowest level since 1951,³ with supplies already constrained by years of drought, herd reductions, and rising production costs.

In areas where NWS is endemic, Lee noted, beef producers can lose 10% to 30% of their livestock solely due to the parasite. "That is a margin that in the United States is not a sustainable loss long term," he said in an interview with dvm360.

Historical estimates illustrate the potential scale of those losses. USDA analyses have estimated that an outbreak comparable to the 1976 Texas infestation could cost producers approximately $732 million annually and result in roughly $1.8 billion in broader economic losses.⁴ USDA has also projected cattle prices will continue to rise as supplies remain limited.

Live animal exports present a particular vulnerability. USDA has warned that trading partners that are currently free of NWS could restrict imports of live animals from affected areas as detections accumulate. "Certain countries may not want to import meat once we have screwworm within our borders," Lee told dvm360. "When we think about live animal export, that risk is higher."

On food safety, USDA officials have emphasized that the US food supply is not at risk. Screwworms do not infest meat, fruits, vegetables, or other food products, and any affected animal would be identified during USDA Food Safety and Inspection Service inspection before entering commerce.¹

The road to re-eradication

The USDA and TAHC have activated a unified incident command with 75 personnel on the ground and hundreds more providing laboratory, logistics, and operational support nationwide. Per the NWS Response Playbook, each detection triggers a 20-kilometer infested zone with quarantines, movement controls, and heightened surveillance. USDA has activated a sterile fly dispersal facility at Moore Air Base in Edinburg, Texas, with aerial dispersal flights beginning June 9. Ground release chambers are simultaneously deploying 4 million sterile flies per week near detection zones.

Experts cautions that re-eradication could take years. During the original campaign, three production facilities combined to release 600 to 800 million sterile flies per week. "It can take up to a year and a half, two years to get to full production," Lee told dvm360.

"This is probably not a problem that gets solved in the next month," Lee said. "This could realistically be a scenario where we're looking at a couple of years or more."

While officials continue scaling up surveillance and sterile fly releases, Reif emphasized that limiting the parasite's spread will require vigilance across the animal health community.

"We're in this together: veterinarians, livestock owners, pet owners, animal caregivers, and the general public," she said. "We all have a role to play to be vigilant and promptly report to prevent the spread of New World screwworm in the US."

References

1. USDA Confirms Two Additional Cases of New World Screwworm in the United States. News release. USDA. June 8, 2026. Accessed June 8, 2026.
2. Bautista-Alejandre A, Mazzolini C. New World screwworm updates: The latest on government, industry response, new cases. dvm360. June 8, 2026. Accessed June 8, 2026. https://www.dvm360.com/view/new-world-screwworm-updates-the-latest-on-government-industry-response
3. Roeloffs Whitfill M. Screwworm Cases Rise To 4 In Texas—Here’s How It Could Drive Up Beef Prices. Forbes. June 8, 2026. Accessed June 8, 2026. https://www.forbes.com/sites/maryroeloffs/2026/06/08/screwworm-cases-rise-to-4-in-texas-heres-how-it-could-drive-up-beef-prices/
4. Historical Economic Impact Estimates of New World Screwworm in the United States. USDA. January 2025. Accessed June 8, 2026. https://www.aphis.usda.gov/sites/default/files/nws-historical-economic-impact.pdf