Parasiticide receives EUA for prevention and treatment of NWS infestation

Officials with the FDA have issued an emergency use authorization (EUA) for doramectin injection (Dectomax/Dectomax-CA1; Zoetis) for the prevention and treatment of New World screwworm (NWS) infestations in dairy cattle, swine, horses, sheep, and deer. This EUA will be effective until it is revoked or the US Department of Health and Human Services’ declaration that the potential public health emergency presented by NWS justifies the EUA of animal drugs for this purpose is terminated.¹

The EUA indication includes lactating and dry dairy cows, replacement dairy heifers aged 20 months or older, and horses aged at least 1 year. However, this indication excludes calves that will be processed for veal and lactating sheep.¹

NWS is a “devastating pest” that infests warm-blooded animals, according to the US Department of Agriculture (USDA). This parasitic fly lays larvae that burrow into the flesh of living animals, including livestock, pets, wildlife, and, in rare cases, humans. These maggots cause severe wounds and complications that can lead to death.^2-4

Adult screwworms are approximately the size of the common housefly. They are identifiable by their orange eyes, metallic or green bodies, and 3 dark stripes on their backs, according to the USDA.^2,3

Mammals and birds with NWS larvae infestation may show signs such as irritated behavior, head shaking, and a smell of decay. 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 Animal and Plant Health Inspection Service Area Veterinarians in Charge. Animal owners should also report these findings to their veterinarian.^2,4,5

Doramectin injection is a parasiticide that previously received conditional approval from the FDA for the prevention and treatment of NWS infestation in beef cattle, female dairy cattle younger than 20 months, pregnant beef cows, newborn calves, and bulls.⁶ Based on the totality of the scientific evidence available, the FDA has concluded that it is reasonable to believe that doramectin injection may be effective for the EUA’s new indications and species, and the known and potential benefits of the product outweigh its known and potential risks.¹

According to the FDA, food products obtained from animals treated with doramectin injection are safe for human consumption when the conditions of use granted by the EUA are followed. These conditions include adhering to the milk discard time and withdrawal periods to help avoid unsafe drug residues in animal-derived human foods.¹

“Milk taken from lactating dairy cows, dry dairy cows, and replacement dairy heifers during treatment and for 468 hours [19.5 days] after treatment must not be used for human consumption,” the FDA said in a news release.¹

Additionally, food producers must wait the specified number of days after the last dose of doramectin injection before slaughtering treated animals for human consumption. These specifications include the following¹:

• Lactating dairy cows, dry dairy cows, replacement dairy heifers: 35 days
• Swine: 24 days
• Sheep: 35 days
• Deer: 35 days

Livestock producers are encouraged to work closely with their herd veterinarian to implement strategic prevention and control measures. “[NWS] has the potential to bring unprecedented economic and animal health harm to livestock producers,” Michael Lormore, DVM, MS, MBA, head of cattle and pork technical services at Zoetis, said in a news release.⁷ “Our top priority is to support keeping animals healthy and provide timely, efficacious solutions to our customers and partners.”

References

1. FDA issues emergency use authorization for over-the-counter injectable drug for New World screwworm in dairy cattle, horses, swine, sheep, and deer. News release. FDA. May 19, 2026. Accessed May 19, 2026. https://www.fda.gov/animal-veterinary/cvm-updates/fda-issues-emergency-use-authorization-over-counter-injectable-drug-new-world-screwworm-dairy-cattle?utm_medium=email&utm_source=govdelivery
2. Crossley KC. NWS preventive drug for cattle receives the FDA’s emergency use authorization. dvm360. February 5, 2026. Updated February 6, 2026. Accessed May 19, 2026. https://www.dvm360.com/view/nws-preventive-drug-for-cattle-receives-the-fda-s-emergency-use-authorization
3. New World screwworm. USDA. Updated May 6, 2026. Accessed February 5, 2026. https://www.aphis.usda.gov/livestock-poultry-disease/cattle/ticks/screwworm
4. United States and Mexico reach agreement to resume eradication efforts on New World Screwworm. News release. USDA. April 30, 2025. Accessed February 5, 2026. https://www.usda.gov/about-usda/news/press-releases/2025/04/30/united-states-and-mexico-reach-agreement-resume-eradication-efforts-new-world-screwworm
5. Lee C. Screwworms: when the larvae don’t care about boundaries. dvm360. April 11, 2025. Accessed February 5, 2026. https://www.dvm360.com/view/screwworms-when-the-larvae-don-t-care-about-boundaries
6. Dectomax-CA1 injectable conditionally approved for New World screwworm. Zoetis. Accessed May 19, 2026. https://www.zoetisus.com/content/_assets/docs/Cattle/New-World-Screw-Worm-Dectomax-Sell-Sheet.pdf
7. Zoetis receives conditional approval for Dectomax-CA1 injectable for the prevention and treatment of New World screwworm myiasis in cattle. News release. Zoetis. September 30, 2025. Accessed May 19, 2026. https://news.zoetis.com/press-releases/press-release-details/2025/Zoetis-Receives-Conditional-Approval-for-Dectomax-CA1-Injectable-for-the-Prevention-and-Treatment-of-New-World-Screwworm-Myiasis-in-Cattle/default.aspx