FDA authorizes Negasunt Powder for New World screwworm under emergency use

The FDA has issued an emergency use authorization (EUA) for Negasunt Powder (coumaphos, propoxur, and sulfanilamide topical powder) for the prevention and treatment of New World screwworm (NWS) myiasis, the latest in a series of regulatory actions the agency has taken since declaring the parasite a significant public health threat last August.

The authorization covers a broad range of species, including cattle, swine, goats, sheep, horses, donkeys, domestic hybrid equids such as mules, and captive wild, exotic, and zoo mammals.¹ Negasunt Powder is sponsored by Elanco, based in Indianapolis, Indiana.

The EUA, issued on April 27, 2026, comes 3 days after the FDA issued another EUA for F10 Antiseptic Barrier Ointment With Insecticide on April 24,² and continues a regulatory push that began in December 2025 following an emergency declaration made by the Department of Health and Human Services (HHS) in August of that year.³

Threat context

NWS (Cochliomyia hominivorax) was eradicated from the United States decades ago, but has been advancing northward since 2022. By fall 2025, confirmed cases had reached Nuevo León, a Mexican border state adjacent to Texas, which included a calf infestation. The larvae feed on living tissue, causing progressive wounds that may be fatal without treatment.

Currently, no NWS-infested zones have been confirmed within US borders. Still, federal agencies continue to monitor the southern border, with the US Department of Agriculture (USDA) deploying sterile fly releases, including from a newly completed dispersal facility in Edinburg, Texas, and jointly monitoring nearly 8000 traps with Mexican authorities. Earlier this month, the US Army Corps of Engineers also announced a ceremonial groundbreaking for a sterile fly production facility at Moore Air Base, which officials expect to be fully operational by November 2027 and to produce approximately 300 million sterile flies weekly.⁴

Authorization and access

Distribution of Negasunt Powder will be routed exclusively through the USDA, which will allocate it to authorized users. Prior to any US incursion, access is limited to employees of federal, state, and local agencies, and of federally recognized tribal agencies, and to those working under their direct authority.

Should NWS establish itself within US borders, licensed veterinarians practicing in USDA-designated infested zones or adjacent surveillance zones—as defined in the USDA's NWS Response Playbook—would also be authorized to obtain and use the product.

Safety and food safety considerations

Two active ingredients, coumaphos and propoxur, pose a neurotoxicity risk to humans, animals, and the environment. The FDA has issued a boxed warning for the product and established specific requirements for its use and disposal. Veterinarians and authorized users should review the full fact sheet before use. Food safety withdrawal requirements are as follows¹:

• Slaughter: Treated animals must not be slaughtered for human consumption within 28 days of the last treatment.
• Milk: A milk discard time has not been established; do not use in animals producing milk for human consumption.
• Veal: A withdrawal period has not been established in preruminating calves; treated calves and calves born to treated cows must not be processed for veal.

The EUA remains in effect until revoked or until the HHS Secretary terminates the underlying emergency declaration. More information on Negasunt Powder, including the full fact sheet, can be found here.

References

1. FDA issues emergency use authorization for topical powder to prevent and treat New World screwworm in multiple species. FDA. April 27, 2026. Accessed April 27, 2026. https://www.fda.gov/animal-veterinary/cvm-updates/fda-issues-emergency-use-authorization-topical-powder-prevent-and-treat-new-world-screwworm-multiple
2. Mazzolini C. FDA grants EUA for antiseptic barrier ointment against New World screwworm. dvm360. April 24, 2026. Accessed April 27, 2026. https://www.dvm360.com/view/fda-grants-eua-for-antiseptic-barrier-ointment-against-new-world-screwworm
3. HHS. Declaration of emergency pursuant to the Federal Food, Drug, and Cosmetic Act for New World screwworm. Federal Register. August 20, 2025. Accessed April 27, 2026. https://www.federalregister.gov/documents/2025/08/20/2025-15918/declaration-of-emergency-pursuant-to-the-federal-food-drug-and-cosmetic-act-for-new-world-screwworm
4. Coppock KC. US sterile fly production facility is under construction. dvm360. April 24, 2026. Accessed April 27, 2026. https://www.dvm360.com/view/us-sterile-fly-production-facility-is-under-construction