The United States Food and Drug Administration has issued its 11th Emergency Use Authorization in the ongoing fight against New World Screwworm, a parasitic fly that was eradicated from the continental United States decades ago but has re-emerged as an active threat to American livestock. The July 15, 2026 EUA authorizes Ivermectin Liquid for Horses (ivermectin oral solution) for the short-term prevention of New World Screwworm infestations in horses when administered within 24 hours of birth or during initial wound care, according to the FDA press announcement.
The authorization applies only to horses and is prescription-only. It does not authorize the product for use in other species, and it is authorized for prevention of new infestations, not for treatment of wounds already infested with larvae.
Why This Matters
New World Screwworm (Cochliomyia hominivorax) is one of the most destructive parasites in North American livestock history. The female fly lays eggs in the open wounds or natural body openings of living warm-blooded animals, including horses, cattle, deer, dogs, cats, and, in rare cases, humans. The larvae burrow into the surrounding living tissue, feeding and multiplying, and what begins as a small wound can progress to a severe, life-threatening infestation within days if untreated.
The fly was eradicated from the United States in the 1960s through a landmark biological control program using sterile male flies. That eradication was among the most successful agricultural pest control programs in U.S. history. Its return, driven by detected cases in Mexico and then along the southern U.S. border, represents the type of agricultural emergency that the FDA has been responding to with escalating urgency since early 2026.
Eleven EUAs in a matter of months signal a federal response to a threat that is not contained. Each EUA adds a new tool or a new species-specific authorization to the response toolkit, and each reflects the FDA's assessment that the threat remains credible enough to justify emergency authorization rather than waiting for standard approval timelines.
"The Trump administration will use every available tool to stop New World screwworm from threatening America's horses and livestock," said HHS Secretary Robert F. Kennedy Jr. in the FDA announcement.
What We Know So Far
The FDA's July 15 EUA is specifically for Ivermectin Liquid for Horses, an oral solution of ivermectin that is administered to horses within 24 hours of birth to protect the vulnerable umbilical area, or at the time of initial wound care to protect open wounds from fly infestation. Acting FDA Commissioner Kyle Diamantas noted in the announcement that "this marks the FDA's 11th Emergency Use Authorization deployed against New World screwworm."
Prior EUAs in this response cycle have covered multiple species and product types:
- Negasunt Powder (coumaphos, propoxur, and sulfanilamide topical powder) for prevention and treatment in cattle, swine, goats, sheep, horses, donkeys, and domestic hybrid equids (April 27, 2026)
- F10 Antiseptic Wound Spray for prevention and treatment in cattle, horses, hoof stock, and wild and pet birds (March 10, 2026)
- Dectomax/Dectomax-CA1 (doramectin injection) for prevention and treatment in dairy cattle, swine, horses, sheep, and deer (May 19, 2026)
- IVOMEC 1% Injection (ivermectin) for cattle (first EUA, early 2026)
The July 15 ivermectin oral solution EUA specifically addresses horses at the most vulnerable moments: newborn foals, whose healing umbilical stumps attract screwworm flies, and horses undergoing any surgical or wound procedure that leaves open tissue.
Confirmed New World Screwworm cases in the United States have been documented in Texas and New Mexico as of available data, with cases in dogs, goats, and cattle confirmed. Florida has also been under heightened surveillance following proximity to Mexico-originating populations.
Where the Risk Is Highest
New World Screwworm risk is highest in states with:
- Proximity to Mexico, where the fly is still present
- Warm, humid conditions that support fly survival
- High livestock and equine populations
Texas, New Mexico, Arizona, and Florida are the states at highest risk based on geography and climate. California has also been identified as a state where surveillance has been heightened. Livestock and equine operations in these states are the primary target of both the screwworm prevention tools and the federal surveillance program.
Equine operations face particular risk because horses often have wounds from fence injuries, dental procedures, hoof work, and castrations. Newborn foals have fresh umbilical wounds that are a primary fly attraction site. Trail horses and horses used in hunting or outdoor recreation in border states face environmental exposure not seen in primarily indoor or urban equestrian settings.
What Doctors and Vets Say
The FDA noted in the EUA documentation that the veterinary review concluded there is sufficient scientific evidence to believe ivermectin oral solution may be effective for the short-term prevention of NWS infestations in horses, and that its potential benefits outweigh the known and potential risks when used as directed.
The EUA is limited to short-term prevention, meaning a single-dose application at the time of birth or wound care, not ongoing suppressive treatment. If infestation occurs despite preventive treatment, or if a wound is already infested at the time of initial care, ivermectin liquid for horses is not authorized for treatment and veterinary consultation is required to determine the appropriate treatment approach.
The USDA has emphasized that New World Screwworm infestations are reportable conditions and that any suspected case should be reported immediately to USDA's Animal and Plant Health Inspection Service (APHIS) at 1-866-4-US-SCREWWORM (1-866-487-7396).
What the Evidence Shows and What It Does Not
MedicalDaily Evidence Check
- Regulatory action type: FDA Emergency Use Authorization (EUA) for an animal health product
- Product authorized: Ivermectin Liquid for Horses (ivermectin oral solution)
- Date of EUA: July 15, 2026 (the 11th NWS EUA in the current response)
- Species authorized: Horses only; not approved for use in other species
- Use authorized: Short-term prevention of NWS infestation; must be administered within 24 hours of birth or at time of initial wound care
- Use NOT authorized: Treatment of existing infestations; use in species other than horses; ongoing suppressive therapy
- Confirmed U.S. cases: Dogs, goats, and cattle in Texas and New Mexico (as of available USDA data)
- What it shows: An active, escalating federal response (11 EUAs) to a parasitic fly threat that has been confirmed in multiple species in at least two U.S. states
- What it does not show: Whether NWS is establishing a stable breeding population in the United States or whether containment is succeeding; USDA surveillance data will determine this over the coming months
- Human risk: Rare but documented; humans can be infested, particularly through wounds or nasal/oral exposure. This is not a common public health threat for most Americans.
- What readers should know: Horse owners and livestock producers in Texas, New Mexico, and border states should contact their veterinarian about NWS prevention now. Any suspected animal infestation should be reported to USDA immediately.
Who Faces the Greatest Risk?
The animals most at risk from NWS infestation are:
- Newborn foals and calves with fresh umbilical wounds
- Horses with open wounds from surgery, injury, dental work, castration, or other procedures
- Cattle, goats, and sheep with any open wound
- Wildlife in affected areas, including deer
- Pets (dogs and cats) with wounds in affected states
Rare human cases typically involve people with open wounds who spend time in areas where the fly is active. Most documented human NWS cases in modern history have occurred in travelers returning from regions of Central or South America where the fly is endemic, not in U.S. residents. The current domestic emergence creates a new theoretical risk for U.S. residents with open wounds in affected areas.
Symptoms of NWS Infestation to Watch For in Animals
Horse owners and livestock producers should watch for:
- Unusual wound behavior: a wound that appears to grow larger, deeper, or more severe rather than healing
- Foul odor from a wound that was healing
- Unusual restlessness or pain in an animal with any wound
- Visible larvae (maggots) in a wound — these may appear cream-colored and spiral-shaped
- Swelling and tissue death around a wound site
- Animals rubbing a wound excessively
Any wound showing these signs should prompt immediate veterinary evaluation. Delayed treatment allows larvae to burrow deeper into tissue and increases mortality risk.
For human exposure concern, any person who develops an unexplained wound with increasing severity, particularly after outdoor activity in Texas, New Mexico, or other border states, should seek medical evaluation and disclose their geographic location and any potential wound exposure.
What You Can Do Now
- Horse owners in Texas, New Mexico, and other border states should contact their veterinarian about obtaining prescription ivermectin oral solution under the July 15 EUA before foaling season or ahead of any planned procedures that involve open wounds.
- Report any suspected NWS infestation in any animal immediately to USDA APHIS at 1-866-4-US-SCREWWORM (1-866-487-7396).
- Monitor the USDA APHIS New World Screwworm tracking page for the most current confirmed detection map.
- Implement standard fly control measures on equine and livestock operations: wound care protocols, clean bedding, prompt treatment of all injuries, and minimizing conditions that attract flies.
- People with open wounds who spend time outdoors in affected states should keep wounds properly covered and seek evaluation if any wound shows unusual progression.
Cost and Access: What Patients Should Know
Ivermectin Liquid for Horses under this EUA is a prescription product. Horse owners need a veterinary prescription to obtain it. Veterinarians in affected states should be familiar with the EUA; owners who have difficulty obtaining a prescription should contact their state veterinarian's office or USDA APHIS for guidance.
For livestock producers facing confirmed or suspected NWS infestations, USDA APHIS provides an emergency response hotline and has stated it will work directly with producers to facilitate access to authorized prevention and treatment products.
What Happens Next
USDA surveillance data will determine whether the confirmed U.S. cases represent an isolated incursion or the beginnings of population establishment. The sterile insect release program that eradicated NWS in the 1960s may be reactivated in border areas; USDA has cited this tool in its response planning. Additional EUAs may be issued as the FDA and USDA identify additional species-specific needs. MedicalDaily will report on new confirmed U.S. case reports, additional EUAs, and any changes to the USDA containment status.
The Bottom Line
The FDA's 11th Emergency Use Authorization for New World Screwworm specifically authorizes ivermectin oral solution as a prescription preventive treatment for horses within 24 hours of birth or at the time of initial wound care. With confirmed NWS cases in dogs, goats, and cattle in Texas and New Mexico, horse owners and livestock producers in border states face a real and active threat from a parasite whose larvae destroy living tissue. Veterinary consultation, prophylactic treatment for vulnerable animals, and immediate reporting of any suspected infestation are the three most important actions available right now.
