The AAEP Infectious Disease Committee has prepared this overview of currently available prevention and treatment options that equine veterinarians may consider for New World Screwworm (NWS) in horses. It is intended as a practical reference to support clinical decision-making during preparedness planning and, if needed, response to a confirmed incursion.
Because product availability and regulatory status continue to evolve, practitioners should consult current guidance from the U.S. Food and Drug Administration (FDA) and the U.S. Department of Agriculture (USDA) when selecting and using products for NWS prevention, treatment, and environmental control.
The information below reflects currently identified options for equine use, including approved, conditionally approved, and emergency use authorized products, as well as examples of EPA-registered pesticides that may support fly control where labeled. These options should be used within the context of an overall biosecurity and wound-management plan, with careful attention to label directions
Preventative and Therapeutic Treatments for Horses
The Food and Drug Administration’s Center for Veterinary Medicine is working with animal drug sponsors to identify potential products for approval/authorization for the prevention or treatment of New World Screwworm myiasis.
Product availability for NWS may include conditionally approved drugs, emergency use authorized products, and, where legally appropriate, extra-label use of FDA-approved animal drugs under a valid veterinary-client-patient relationship and applicable regulations.
The current challenge is lack of published specific studies or research in horses for New World Screwworm. More concerning is that there are no studies on the duration of efficacy for any product for the long-term prevention of screwworm infestation.
In the event of a confirmed screwworm incursion in the United States, the limited authorized products for practitioners’ consideration are the following:
- Dectomax injectable – Emergency Use Authorization for the Prevention of NWS Myiasis in horses at least 1 year of age.
- F10 Antiseptic Wound Spray with Insecticide (topical)- Emergency Use Authorization for prevention and treatment of NWS Myiasis in horses.
- F10 Antiseptic Barrier Ointment with Insecticide (topical)- Emergency Use Authorization for Prevention and Treatment of NWS myiasis in horses.
- Negasunt Powder (topical) – Emergency Use Authorization for prevention and treatment of NWS myiasis in horses.
Note: Oral Ivermectin has been historically used in other countries for treatment and prevention of New World Screwworm; however, there have been no published studies documenting the efficacy of this product in horses. Practitioner use of the product for the prevention of screwworm would be considered extra-label use. Judicious use of avermectins considers the likelihood of resistance of clinically relevant internal parasites of horses.
This list will be updated as additional products become available. For the most current list of conditionally approved or authorized products for NWS treatment and prevention, click here.
Pesticides for Control of New World Screwworm
Several pesticides are currently registered by the Environmental Protection Agency for use against screwworm. Examples of approved equine-labeled products and their active ingredient include but not limited to:
- Claire Bed Bug, Lice and Dust Mite Spray (PLZ Corp.) - Active Ingredient: Permethrin
- Co-Ral Coumaphos Flowable Insecticide (Elanco US, Inc.) - Active Ingredient: Coumaphos
- Permethrin Insecticide Spray (Elanco US, Inc.) - Active Ingredient: Permethrin
An example of an approved product for the outside surfaces of buildings and perimeter treatment is EP152 EW Insecticide (Environmental Science US LLC) with active ingredient Zeta-Cypermethrin. Additionally, DeltaGard Fly Insecticide products (Environmental Science US LLC) with active ingredient Deltamethrin is approved for this use.
For a complete list of the current approved products, click here.
Additional Considerations
Currently available prevention and treatment options for New World Screwworm in horses remain limited and are supported by evolving regulatory pathways rather than a robust equine-specific evidence base.
Veterinarians should interpret these options cautiously and rely on the most current guidance from the FDA, USDA and state animal health officials. Any product use should be incorporated into a broader strategy that includes prompt wound care, fly control, surveillance, and sound biosecurity practices.
As additional data and products become available, recommendations may change, making continued review of official resources essential for informed clinical decision-making.
Any prevention and treatment recommendation may be dictated by state or federal animal health officials. Visit the USDA www.screwworm.gov website or your state veterinarian’s webpage for the most up-to-date guidance for NWS prevention and response.
