New World screwworm has been confirmed in the United States again, with Texas and New Mexico detections tracked by the USDA, and Arizona horse owners should now operate in a heightened vigilance posture rather than a business-as-usual one. The practical response comes down to three things: checking wounds properly, understanding the movement rules that now apply, and knowing when a veterinarian must be called.
Table of Contents
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What is New World screwworm and why is it a threat to horses?
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Where has New World screwworm been confirmed in the United States?
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How should I check my horse for wounds during a screwworm alert?
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What are the movement rules for horses in or near an infested area?
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Are there authorised preventives for New World screwworm in horses?
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How does Equine Salt Therapy support equine respiratory and recovery care?
What is New World screwworm and why is it a threat to horses?
New World screwworm is caused by the larvae of Cochliomyia hominivorax, which invade and consume living tissue rather than dead tissue, according to The Equine Practice Company. That distinction is what makes this pest so dangerous to horses and other warm-blooded animals.
The lifecycle moves quickly. Screwworm eggs hatch in roughly 24 hours, and the larvae then feed on live tissue for approximately seven days before dropping to the ground to pupate and become flies, according to US Equestrian. A wound that looks minor at morning feed can be actively infested by the next day.
New World screwworm is a reportable, economically significant pest. It was eradicated from the United States in the 1960s through the sterile insect technique, and a later outbreak in the Florida Keys was eliminated in 2017, according to The Equine Practice Company. The 2026 situation is a re-entry, not a theoretical risk.
The USDA confirmed that New World screwworm had entered the United States on 3 June 2026 with a case in Texas, according to US Equestrian. For Arizona horse owners, that confirmation changed the risk calculation for any horse with a wound.
Where has New World screwworm been confirmed in the United States?
The USDA has confirmed 11 cases of New World screwworm in animals within the United States, including 10 in Texas and one in New Mexico, according to The Equine Practice Company. No Arizona cases had been confirmed at the time of the most recent dashboard update.
APHIS reports cases through an individual-animal dashboard organised by county and state, animal type and species, confirmation date, and status. The dashboard also captures fly traps with at least one New World screwworm wild fly detected, according to APHIS.
The dashboard distinguishes between active and inactive animal cases. Active cases involve ongoing disease mitigation efforts until the animal is free of New World screwworm myiasis, while inactive cases are those where mitigation is no longer required, according to APHIS.
The APHIS dashboard was last modified on 21 August 2026. It is not intended to support international trade, so it functions as a situational awareness tool rather than a movement certificate, according to APHIS.
What does New World screwworm look like in a horse’s wound?
Horse owners should look for wounds that are not healing as expected and the presence of larvae within living tissue, according to The Equine Practice Company. The key visual difference is that screwworm larvae burrow into healthy flesh rather than sitting on the surface of dead material.
The core distinction is that screwworm larvae feed on live tissue, which separates a genuine concern from ordinary fly strike on necrotic material, according to The Equine Practice Company. A wound with maggots is not automatically screwworm, but the location and behaviour of the larvae matter.
The research base for horse-specific clinical progression is thin, so owners should err toward veterinary assessment rather than home diagnosis, according to The Equine Practice Company. What looks like a routine summer sore can deteriorate quickly.
The lifecycle timing is a practical check. A 24-hour hatch window means a wound can change fast between daily inspections, according to US Equestrian. Photographs taken at the same time each day are the most reliable way to judge that change.
How should I check my horse for wounds during a screwworm alert?
A full-body, hands-on inspection routine is the standard, not a glance from the gate. Run your hands over the horse from poll to tail, checking the sites owners commonly miss: the sheath or udder, the coronary bands, the ears, under the jaw, the armpits, and any old scar tissue.
Photograph and date any wound so change over 24 hours can be judged objectively. The roughly 24-hour egg hatch window means a wound can go from clean to infested between one afternoon and the next, according to US Equestrian.
Set a stricter inspection rhythm for horses recently arrived from or returning to a state with a confirmed case. Those horses warrant twice-daily checks for at least the first 14 days, according to US Equestrian.
Early detection supports the prevention window described in the FDA authorisations, which are for use at the appearance of a wound or at castration, according to The Equine Practice Company. Finding a wound on day one is materially different from finding it on day three.
What are the movement rules for horses in or near an infested area?
Once a case is confirmed, state animal health veterinarians and the USDA draw a 20-kilometre, or 12-mile, radius around the case as an infested area, according to US Equestrian. Movement within and out of that area is no longer routine.
Horses that have been in a state with a confirmed screwworm case in the past 14 days may be subject to documentation of veterinary inspection requirements, according to US Equestrian. That means a certificate of veterinary inspection may be required even for travel that previously needed no paperwork.
Finalised state and federal movement protocols within an infested area, and state-specific inspection and treatment requirements, remain open questions. Horse owners should confirm current requirements with their state animal health authority before moving any horse, according to US Equestrian.
Some states restrict animal gatherings or effectively prohibit horse shows within infested areas, and this varies by jurisdiction, according to US Equestrian. A show that is running in one county may be cancelled or restricted in the next.
Are there authorised preventives for New World screwworm in horses?
Yes, but only for prevention, not treatment. On 31 August 2026, the FDA published notice in the Federal Register covering three Emergency Use Authorizations for animal drugs used in the New World screwworm response, according to The Equine Practice Company.
Dectomax/Dectomax-CA1, a doramectin injection sponsored by Zoetis, is authorised for prevention of New World screwworm myiasis in horses one year of age and older, at the appearance of a wound or at the time of castration. The duration of protection beyond 24 hours remains unknown, according to The Equine Practice Company.
Ivermectin Liquid for Horses, an ivermectin oral solution sponsored by Alberta Vet Labs, is authorised by prescription for short-term prevention in newborn foals within 24 hours of birth, or in horses of any age at initial wound care. The FDA estimates protection lasts no more than 24 hours, according to The Equine Practice Company.
Neither Dectomax nor Ivermectin Liquid for Horses is authorised to treat an existing New World screwworm infestation in horses, according to The Equine Practice Company. A horse with active larvae needs a veterinarian, not a preventive dose.
When should I call a veterinarian about a suspected case?
Call a veterinarian when a wound has larvae present, when a wound is deteriorating despite normal care, when any horse with a wound has been in a confirmed-case state in the past 14 days, or when any horse is inside a declared infested area, according to The Equine Practice Company and US Equestrian.
Treatment of an existing infestation is a veterinary matter because the authorised products are prevention-only, according to The Equine Practice Company. There is no over-the-counter or authorised farm treatment for active screwworm myiasis.
Confirmation triggers a formal response and infested-area declaration, so a call is a disease-control action, not just a clinical one, according to US Equestrian. Reporting a suspect case protects every other horse in the district.
Have documentation ready when you call, given the 14-day veterinary inspection requirements for recent travel from affected states, according to US Equestrian. Travel history, wound photographs, and any treatment records will help the veterinarian assess the case quickly.
How does Equine Salt Therapy support equine respiratory and recovery care?
Equine Salt Therapy positions salt therapy as a complementary wellbeing and recovery aid for horses in training, rehabilitation and breeding programs. It is not a wound treatment and not a screwworm preventive.
The Ultisalt™ dry salt aerosol delivery system uses a fine mist of treatment salt distributed through the room via a halo-generator. The standard protocol is a 15-minute session over three consecutive days, supporting respiratory comfort and recovery in equine athletes.
Equine Salt Therapy offers Licensed Business Opportunities and Master Licenses across Equine, Poultry, Swine and Companion Animals. Territories are sold under license, with pricing from $110,000 to $1,000,000. Treatments start at $100 per horse.
The platform is protected by granted patents in multiple jurisdictions, with the precise scope of protection defined by the claims of each applicable patent. The Ultisalt™ system ties the acronym DSAT, Dry Salt Aerosol Therapy, to the Animal Kingdom.
Key Takeaways
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New World screwworm is caused by Cochliomyia hominivorax larvae, which feed on living tissue rather than dead tissue.
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The USDA has confirmed 11 cases in animals in the United States, including 10 in Texas and one in New Mexico.
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Screwworm eggs hatch in roughly 24 hours and larvae feed for about seven days before dropping to the ground to pupate.
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A confirmed case triggers a 20-kilometre, or 12-mile, infested area drawn by state animal health veterinarians and the USDA.
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Horses that have been in a confirmed-case state in the past 14 days may face veterinary inspection documentation requirements.
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Dectomax and Ivermectin Liquid for Horses are authorised for prevention only, not for treating an existing infestation.
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The FDA estimates protection from Ivermectin Liquid for Horses lasts no more than 24 hours, and Dectomax duration beyond 24 hours is unknown.
References
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New World Screwworm: What Equine Veterinarians Need to Know — The Equine Practice Company
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New World Screwworm: What Horse Owners Need to Know — US Equestrian, 13 October 2026
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Confirmed Detections of New World Screwworm — APHIS, 21 August 2026
