NWS preventive drug for cattle receives the FDA’s emergency use authorization

Officials with the FDA have granted Emergency Use Authorization (EUA) for a parasiticide to help prevent New World screwworm (NWS) infestation in cattle. Ivermectin injectable solution (Ivomec 1%; Boehringer Ingelheim Animal Health) is an over-the-counter drug that was previously approved by the FDA to treat and control more than 30 parasite species and stages in cattle, as well as uses for swine, reindeer and American bison.1,2

NWS is a “devastating pest” that infests warm-blooded animals, according to the USDA. This parasitic fly lays larvae that burrow into the flesh of living animals that include livestock, pets, wildlife, birds and, in rare cases, humans. These maggots cause severe wounds and complications that can lead to death.3,4

Adult screwworms are the approximate size of a common housefly. They are identifiable by orange eyes, a metallic or green body, and 3 dark stripes on their backs, according to the USDA.4 In a dvm360 article, author Christopher Lee, DVM, MPH, DACVPM, said NWS can also be identified by the “prominent hooks on its anterior end— imagine a vampire maggot.” He noted that although many maggots have hooks, they are large on NWS.5

Mammals and birds with NWS larvae infestation may show signs that include irritated behavior, head shaking, and a smell of decay.4 Signs of infestation, evidence of a fly strike and the presence of maggots in wounds should be reported by animal health professionals to state animal health officials and APHIS Area Veterinarians in Charge. Animals owners should also report these findings to their veterinarian.4,5

“Having worked in regions where New World screwworm is endemic, I’ve seen firsthand that effective readiness depends on access to preventive tools and strong producer education,” Gustavo Sabatini, PhD, MBA, MS, global technical manager for ruminant parasiticides for Boehringer Ingelheim, said.6 “Screwworm strikes cattle when they are most vulnerable, including at birth, and demands more labor‑intensive management on the ground. That’s why prevention is essential – not only to protect animal health, but also to safeguard the food supply and the livelihoods of cattle producers.”

Based on available scientific evidence, FDA officials found ivermectin may be effective for preventing NWS larvae infestations in cattle when the drug is administered with 24 hours of birth, at the time of castration or when a wound appears. The known and potential benefits outweigh the drug’s known and potential risks, according to the agency.1

The drug should not be used for female dairy cattle producing milk for human consumption nor calves that will be processed for veal, according to the FDA. The slaughter withdrawal period is 35 days for cattle.1

“Emergency Use Authorization for Ivomec (ivermectin) 1% Injection provides cattle producers and veterinarians with an important preventive tool against New World screwworm. We appreciate the proactive approach of the FDA and USDA in response to this emerging animal health threat and remain dedicated to supporting veterinarians, producers, and government as we work together to protect cattle herds,” Steve Boren, Vice President, US livestock for Boehringer Ingelheim, said.6

In September 2025, the FDA issued a conditional approval for a drug indicated to prevent and treat NWS larval infestations in cattle. Doramectin injection solution (Dectomax-CA1 Injectable; Zoetis) is also indicated for the prevention of NWS reinfestation for 21 days in cattle.7

“New World screwworm has the potential to bring unprecedented economic and animal health harm to livestock producers,” Mike Lormore, DVM, MS, MBA, head of cattle and pork technical services at Zoetis, said.7 “Our top priority is to support keeping animals healthy and provide timely, efficacious solutions to our customers and partners.”

Additionally, the FDA has issued EUAs for other drugs for prevention of NWS infestation in companion animals. These include lotilaner (Credelio; Elanco) for treating NWS infestation in dogs8, and lotilaner chewable tablets (Credelio Cat; Elanco) for treating feline infestation of NWS larvae9, both of which require a prescription.

Furthermore, lotilaner, moxidectin, praziquantel and pyrantel chewable tablets (Credelio Quattro; Elanco) received the FDA’s conditional approval for treating NWS larvae infestation in dogs.10 “Credelio Quattro is indicated for use in dogs and puppies 8 weeks of age and older, 3.3 pounds or greater,” Casey Locklear, DVM, US medical strategic lead for Elanco Animal Health, said in an earlier dvm360 interview.11

To address the threat of NWS infestation in the US, Texas Governor Greg Abbott issued a statewide disaster declaration in January 2026, following cases reported in northern Mexico. "Although the New World screwworm fly is not yet present in Texas or the US, its northward spread from Mexico toward the US southern border poses a serious threat to Texas' livestock industry and wildlife," Abbott said in a news release. "With this statewide disaster declaration, the Texas NWS Response Team can fully utilize all state government prevention and response resources to prevent the re-emergence of this destructive parasite. Texas is prepared to fully eradicate this pest if need be."12

The US is also addressing the threat of NWS infestation by opening a sterile fly dispersal facility in Mexico. Announced in November 2025, the facility allows the USDA to disperse sterile flies aerially across northeastern Mexico, thus preventing infestation in the US.7

Two methods are used to disperse sterile insects: aerial dispersal and ground release chambers. “Aerial operations are preferred because they allow for dispersal at a steady rate through a large area, and because sterile insects may be dispersed in areas that are unreachable from the ground,” USDA officials said in a news release.7

The USDA is also responding to the threat of NWS infestation with the construction of a domestic sterile fly facility at Moore Air Base in Edinburg, Texas. This facility is projected to open and begin sterile fly production in 2026.7

References

1. FDA issues Emergency Use Authorization for over-the-counter injectable to prevent New World screwworm in cattle. News release. FDA. February 5, 2026. Accessed February 5, 2026. https://www.fda.gov/animal-veterinary/cvm-updates/fda-issues-emergency-use-authorization-over-counter-injectable-drug-prevent-new-world-screwworm?utm_medium=email&utm_source=govdelivery
2. Ivomec (ivermectin). Boehringer Ingelheim. Accessed February 5, 2026. https://bi-animalhealth.com/cattle/products/ivomec
3. United States and Mexico reach agreement to resume eradication efforts on New World Screwworm. News release. USDA. April 30, 2025.
4. New World screwworm. US Department of Agriculture. April 3, 2025. Accessed February 5, 2026. https:// www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm
5. Lee C. Screwworms: when the larvae don’t care about boundaries. April 11, 2025. Accessed February 5, 2026. dvm360. https://www.dvm360.com/view/screwworms-when-the-larvae-don-t-care-about-boundaries
6. Boehringer Ingelheim secures Emergency Use Authorization for Ivomec (ivermectin) 1% Injection to help protect cattle against New World screwworm. News release. Boehringer Ingelheim. February 5, 2026.
7. Crossley KC. USDA opens sterile fly dispersal facility in Mexico. dvm360. November 14, 2025. Accessed February 5, 2026. https://www.dvm360.com/view/usda-opens-sterile-fly-dispersal-facility-in-mexico
8. Bautista-Alejandre A. Antiparasitic receives FDA emergency authorization to treat New World screwworm in cats. dvm360. November 21, 2025. Accessed February 5, 2026. https://www.dvm360.com/view/antiparasitic-receives-fda-emergency-authorization-to-treat-new-world-screwworm-in-cats
9. Bautista-Alejandre A. FDA grants emergency use authorization for lotilaner to treat New World screwworm in dogs. dvm360. October 24, 2025. Accessed February 5, 2026. https://www.dvm360.com/view/fda-grants-emergency-use-authorization-for-lotilaner-to-treat-new-world-screwworm-in-dogs
10. Crossley KC. FDA conditionally approves combination parasiticide for New World screwworm. dvm360. December 18, 2025. Accessed February 5, 2026. https://www.dvm360.com/view/fda-conditionally-approves-combination-parasiticide-for-new-world-screwworm
11. Locklear C, Crossley KC. Novel therapy protects against 6 parasites. dvm360. February 25, 2025. Accessed February 5, 2025. https://www.dvm360.com/view/novel-therapy-protects-against-6-parasites
12. Governor Abbott issues disaster declaration to prevent New World screwworm fly infestation. Office of the Texas Governor. January 29, 2026. Accessed February 5, 2026. https://gov.texas.gov/news/post/governor-abbott-issues-disaster-declaration-to-prevent-new-world-screwworm-fly-infestation