New World Screwworm Has Reached Texas. Here Is What Every Horse Owner Needs to Know | What It Is, What to Watch For, and How to Protect Your Horses Now
Key Takeaways
- As of June 8th 2026, five screwworm cases have been confirmed across Texas and one in New Mexico, marking the first detections in the continental U.S. in decades¹
- New World Screwworm larvae feed on living tissue, not dead tissue, making them uniquely dangerous to horses, livestock, and other warm-blooded animals
- Any open wound, surgical site, or mucous membrane can serve as an entry point for infestation
- Early detection is critical. Infestations that go untreated can be fatal
- Any suspected case must be reported to your state veterinarian immediately. This is a federally reportable foreign animal disease
- Early detection and response is critical to stop the spread¹
Quick Answer
New World Screwworm is a parasitic fly whose larvae burrow into the living tissue of warm-blooded animals. Unlike common flies that feed on dead or decaying tissue, screwworm larvae feed on living flesh and will continue to damage tissue until treated. The fly lays eggs in open wounds or mucous membranes. Once hatched, the larvae cause rapid, serious damage. Texas horse owners should inspect every horse daily, treat and cover all wounds immediately, and contact their state veterinarian if anything looks suspicious.
What Is New World Screwworm?
New World Screwworm is caused by the larvae of the fly species Cochliomyia hominivorax. The name refers to the corkscrew shape of the larvae as they burrow into tissue. What makes this parasite uniquely dangerous is that the larvae do not feed on dead or decaying tissue. They feed exclusively on the living flesh of warm-blooded animals.
Using sterile insect technique, the United States eradicated New World Screwworm in 1966 and successfully eliminated a small outbreak from the Florida Keys in 2017.³ For most horse owners in the U.S., this has been a distant concern for decades.
That changed on June 3, 2026.
Since 2023, an outbreak of New World Screwworm has moved northward through Central America and Mexico, primarily infesting livestock, pets, and wildlife, but also people.³ As of June 8, 2026, five cases have been confirmed in Texas and one in New Mexico, marking the first detections in the continental U.S. in decades. Early detection and response is critical to stop the spread.¹
How Horses Get Infested
The screwworm fly is attracted to open wounds, surgical sites, and moist mucous membranes. Common entry points in horses include cuts, abrasions, and lacerations, branding or dehorning wounds, surgical incision sites, the nose, eyes, sheath, and other natural body openings, umbilical areas in newborn foals, and tick bites or other minor skin breaks.
The larvae are deposited on wounds or superficial body cavities such as the nose and sheath of horses, where they feed and grow. Untreated wounds often develop multiple infestations which are more likely to kill the animal.¹ The fly lays creamy white eggs at the edges of wounds. Once hatched, the larvae begin feeding and burrowing into tissue within hours. A wound that looks minor can become life-threatening very quickly if screwworm larvae are present.
Signs of Infestation
Know what to look for. These are the signs that warrant immediate veterinary contact and reporting:
- A wound that is getting worse rather than healing
- Foul-smelling discharge from a wound
- Visible maggots or larvae in or around a wound
- Creamy white eggs at the wound edges
- Restlessness, head shaking, or obvious signs of pain around a wound
- Rapid enlargement of a wound
- Swelling, tissue discoloration, or tissue death around the affected area
Any wound that is worsening, smells bad, or contains visible larvae should be treated as a suspected screwworm case until proven otherwise.
What to Do If You Suspect a Case
This is a federally reportable foreign animal disease. Do not attempt to treat it on your own.
Contact your state veterinarian immediately. In Texas, that is the Texas Animal Health Commission at 1-800-550-8242. Federal and state officials will guide you through the appropriate diagnostic testing, treatment protocol, and biosecurity requirements.
Do not allow larvae removed from the wound to enter the environment. Federal and state protocols require that larvae be destroyed according to official guidelines.
Common Fly Larvae vs. New World Screwworm: At a Glance
| Common Fly Larvae | New World Screwworm | |
|---|---|---|
| Feeds on | Dead or decaying tissue | Living tissue only |
| Wound progression | Wound stays stable or improves | Wound rapidly worsens |
| Odor | Minimal | Strong, foul odor |
| Larvae appearance | Varies by species | Cream-colored, corkscrew shape |
| Risk to animal | Low to moderate | High, potentially fatal |
| Reportable disease | No | Yes, federally reportable |
Actionable Checklist: Protecting Your Horses Now
- ✓ Inspect every horse from head to tail daily, paying close attention to any wound, cut, or skin break
- ✓ Clean and cover all wounds immediately, no matter how minor
- ✓ Check moist areas including the nose, eyes, sheath, and any surgical sites
- ✓ Monitor newborn foals closely around the umbilical area
- ✓ Implement consistent fly control in stalls, paddocks, and anywhere horses congregate
- ✓ Maintain clean stalls and remove manure regularly to reduce fly populations
- ✓ Know your state veterinarian contact information before you need it
- ✓ If you see a wound that smells bad, is worsening, or contains visible larvae, call your vet and state officials immediately
- ✓ Do not move potentially infested animals without guidance from animal health officials
Frequently Asked Questions
What is New World Screwworm and why is it dangerous? New World Screwworm is a parasitic fly whose larvae feed exclusively on living tissue. Unlike common flies whose larvae feed on dead tissue, screwworm larvae actively burrow into and destroy living flesh. Untreated infestations can be fatal.
Has New World Screwworm been confirmed in the United States? Yes. On June 3, 2026, the USDA confirmed a case in Zavala County, Texas.¹ This is the first confirmed case in the continental United States in decades and represents a significant development for livestock and horse owners, particularly in Texas and neighboring states.
What wounds are most at risk? Any open wound is a potential entry point. Common targets include cuts, branding wounds, surgical sites, tick bites, and natural body openings including the nose, sheath, and eyes. Newborn foals are particularly vulnerable around the umbilical area.
What does a screwworm infestation look like? A wound that is worsening rather than healing, has a foul smell, or contains visible larvae or creamy white eggs at the wound edges. The wound may enlarge rapidly and the horse may show signs of pain, restlessness, or head shaking.
Is screwworm the same as regular maggots in a wound? No. Common fly larvae feed on dead tissue and are sometimes used therapeutically to clean wounds. Screwworm larvae feed on living tissue and cause progressive, serious damage. Any wound containing larvae should be evaluated by a veterinarian to confirm the species.
What should I do if I suspect my horse has screwworm? Contact your veterinarian and your state veterinarian immediately. Do not attempt to treat it without guidance. This is a federally reportable disease and specific protocols must be followed for treatment, disposal of larvae, and biosecurity.
Can screwworm affect people? No locally acquired human infestations have been reported in the United States.³ However, screwworm can infest people who have open wounds and are in contact with infested animals or in endemic areas. Practicing good wound hygiene and wearing protective clothing when handling potentially infested animals reduces risk.⁴
Are horses being restricted from travel? Movement restrictions are developing rapidly. Canada has suspended imports of livestock including horses originating from or present within Texas within 21 days before entry.² Check with your state animal health officials for the most current movement requirements before hauling horses across state or international borders.
Is there an approved treatment for horses? F10 antiseptic spray and ointment has received FDA emergency use authorization for multiple species including horses.⁵ Treatment should always be directed by a veterinarian and follow the guidance of state and federal animal health officials. Treatment typically involves mechanical removal of larvae, wound cleaning, and approved topical and systemic insecticides.
When to Call Your Veterinarian
Call immediately if you see any wound that is worsening, has a foul odor, contains visible larvae or eggs, or if your horse is showing signs of unusual pain or irritation around a wound. Do not wait. Screwworm infestations progress quickly and early intervention is critical.
Texas horse owners should keep these contacts on hand:
- Texas Animal Health Commission: 1-800-550-8242
- USDA APHIS: aphis.usda.gov
- AAEP Screwworm Resources: aaep.org/guidelines-resources/new-world-screwworm
The Takeaway
New World Screwworm is now on Texas soil. The best thing horse owners can do right now is know the signs, inspect horses daily, treat every wound immediately, and know who to call.
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References
- U.S. Equestrian Federation. Alert: Screwworm Confirmed in the United States. usef.org. June 3, 2026.
- Canadian Food Inspection Agency. Suspension of livestock imports from Texas. June 5, 2026.
- USDA Animal and Plant Health Inspection Service. New World Screwworm. aphis.usda.gov. Accessed June 2026.
- Centers for Disease Control and Prevention. New World Screwworm Outbreak Situation Summary. cdc.gov. April 2026.
- DVM360. New World Screwworm Confirmed in United States. dvm360.com. June 2026.
