FDA Authorizes Emergency Use of Ivermectin to Protect Horses from New World Screwworm

The U.S. Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for Ivermectin Liquid for Horses, providing veterinarians with an additional tool to help protect horses against New World screwworm (NWS) infestations. The emergency authorization is part of the U.S. government’s broader effort to contain the spread of the destructive parasite and safeguard livestock, equine populations and agricultural communities.

The authorization allows the prescription-only oral ivermectin solution to be used for short-term prevention of New World screwworm in two situations:

• Within 24 hours of birth in newborn foals.

• At the time of initial wound care for horses of any age with fresh wounds that may attract screwworm flies.

New World Screwworm Remains a Serious Animal Health Threat

New World screwworm is caused by the larvae of the fly Cochliomyia hominivorax, which feed on the living tissue of warm-blooded animals. Unlike many other fly larvae that consume dead tissue, screwworm larvae invade healthy flesh, creating painful wounds that can rapidly enlarge, cause severe infections and, if left untreated, become fatal.

Livestock such as cattle, sheep, goats and horses are particularly vulnerable, although wildlife, companion animals and, in rare cases, humans can also be affected. The parasite poses significant risks to animal welfare, livestock production and international animal trade.

Emergency Authorization Supports Disease Preparedness

According to the FDA, available scientific evidence suggests it is reasonable to believe that the ivermectin oral solution may provide effective short-term protection against screwworm infestation under the emergency conditions specified in the authorization. The agency concluded that the expected benefits outweigh the known and potential risks in the current disease situation.

The product is available only by prescription from a licensed veterinarian and can be administered either as an oral drench or, when appropriate, through a nasogastric tube.

FDA Emphasizes That Protection Is Temporary

While the authorization provides veterinarians with an important preventive option, the FDA stressed that ivermectin is not a standalone solution.

The agency estimates that the protective effect lasts no more than 24 hours, meaning horses with wounds that remain exposed continue to require additional preventive measures, including:

• Proper wound bandaging

• Fly repellents

• Physical fly barriers

• Ongoing wound monitoring

• Good stable hygiene and fly-control programs

If an animal is already infested with screwworm larvae, the ivermectin solution authorized under the EUA is not intended as a treatment, and veterinarians should consider appropriate therapeutic options.

Part of a Broader Federal Response

The latest authorization builds on a series of FDA emergency actions introduced during the ongoing response to New World screwworm.

Since late 2025, the agency has authorized or conditionally approved several veterinary products targeting screwworm prevention or treatment in multiple animal species, including cattle, horses, dogs and cats. These include injectable antiparasitic drugs, topical sprays, ointments and oral medications designed to expand the range of tools available to veterinarians and livestock producers.

Federal agencies, including the FDA and USDA, continue working together to strengthen surveillance, improve disease preparedness and reduce the risk of further spread across U.S. livestock populations.

Why This Matters for the Animal Health Industry

The FDA’s latest Emergency Use Authorization highlights the growing importance of rapid regulatory action when responding to emerging livestock disease threats.

New World screwworm has long been regarded as one of the most economically damaging livestock parasites because infestations can lead to animal deaths, reduced productivity, increased veterinary costs and trade restrictions. As outbreaks and detections continue to prompt heightened surveillance, regulators are expanding access to preventive veterinary medicines while supporting veterinarians and livestock owners with additional disease-control options.

The authorization also demonstrates how emergency regulatory pathways can accelerate the availability of veterinary products during disease outbreaks, helping protect animal health while reducing the potential economic impact on the livestock industry.