New World screwworm updates: the latest on government, industry response

This is a developing story. dvm360 is tracking the US response to New World screwworm (NWS) and will update this page as new information becomes available. The most recent updates appear first.

New World screwworm, a parasitic fly whose larvae burrow into the living flesh of warm-blooded animals, has reached the United States after a years-long northward advance through Central America and Mexico. The pest was eradicated from the US decades ago, and its return poses a serious threat to livestock, wildlife, and companion animals — as well as, in rare cases, humans. This page consolidates dvm360's ongoing coverage of confirmed detections, the federal and state response, and the treatment and prevention options available to veterinarians. For clinical background, see dvm360's prior reporting on NWS identification, reporting requirements, and the slate of FDA emergency use authorizations issued over the past year.

Here is the latest:

June 4, 2026 — Elanco outlines treatment options available for NWS

Elanco Animal Health announced a portfolio of treatment and prevention options for NWS across livestock and companion animals, several of which received emergency regulatory authorizations ahead of the confirmed US detection.

For dogs: Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, and pyrantel) holds FDA Conditional Approval for treatment of NWS larvae infestations. Credelio (lotilaner) carries an FDA Emergency Use Authorization (EUA) for the same indication.

For cats: Credelio CAT (lotilaner) holds a comparable EUA.

For livestock: Negasunt Powder (coumaphos, propoxur, and sulfanilamide) and Tanidil (coumaphos, propoxur) have received emergency authorizations but will be available exclusively through USDA APHIS and its National Veterinary Stockpile, distributed in coordination with state animal health officials. Catron IV (permethrin), which kills and controls screwworm fly and maggots in livestock, remains available through standard channels under existing EPA approval.

Veterinarians should note that Negasunt Powder carries a neurotoxicity warning requiring full personal protective equipment (PPE) including chemical-resistant gloves and a NIOSH-approved respirator, and treated animals cannot be slaughtered for human consumption within 28 days of last treatment. It is not authorized for use in dogs, cats, birds, or free-ranging wildlife.

"New World screwworm could have a devastating impact on animal health, welfare, and producer livelihoods," said Jeff Simmons, Elanco's President and CEO, adding that the company is working alongside the broader U.S. animal health industry to help fight the parasite.

June 3 - Agriculture groups respond to NWS detection

National farm and livestock organizations responded to the Zavala County detection with a common set of themes: support for USDA's preparation, reassurance on food safety, and calls for a science-based, adequately resourced response.

The National Milk Producers Federation (NMPF) framed the return as an anticipated setback.

"The return of New World screwworm to the United States decades after its initial eradication is a disappointing milestone, but it's also one for which dairy producers have been preparing for more than a year," President and CEO Gregg Doud said.

He stressed that the detection has no effect on food safety, said dairy and other livestock producers pledge close collaboration with USDA and state and local officials, and urged that decisions affecting animal movements follow scientific guidance to avoid economic harm greater than the pest itself. NMPF also asked that adequate resources be devoted to the response.

Oklahoma Farm Bureau (OKFB) President Stacy Simunek called the detection a moment for the agriculture community to come together.

"With today's news of the first case of New World screwworm in the United States in decades, this is a time for farmers, ranchers and our entire agriculture community to work together to ensure this pest is contained and eliminated as quickly as possible," Simunek said.

Simunek urged producers across the state to learn what an infestation would look like on their operation and to step up vigilance, anticipating market volatility from the discovery, and thanked USDA and Secretary Brooke Rollins for the past year's preparatory work while asking the administration to keep prioritizing NWS monitoring and response.

June 3, 2026 — USDA confirms NWS detection in South Texas calf

The US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) confirmed the detection of New World screwworm in a bovine in Zavala County, Texas. The affected animal is a 3-week-old calf, with larvae identified in its umbilical area; APHIS reported no further detections at the time of the announcement. The specimen was sent to USDA's National Veterinary Services Laboratories in Ames, Iowa, for confirmatory testing.

USDA and Texas officials activated a unified Incident Command Team with the Texas Animal Health Commission, establishing a 20-km infested zone around the detection with quarantines, movement controls, and surveillance, and expediting the release of sterile NWS flies in the area. The agency emphasized that the US food supply is not at risk, as screwworms do not infest meat or other food sources. Veterinarians who suspect infestation should contact their state animal health official or USDA area veterinarian in charge immediately. Full coverage here.