A parasitic fly once eradicated from the United States has come back, and your dog or cat could be at risk.
On June 3, 2026, the USDA confirmed the first U.S. case of New World screwworm (NWS) in a Texas calf. The parasite has already spread through Mexico and Central America for the past two years. If you have a pet — especially one who spends time outdoors — here’s what you need to know right now.
What Is New World Screwworm?
New World screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae feed exclusively on the living tissue of warm-blooded animals, including dogs, cats, and people. This is what makes it so dangerous: unlike regular flies that go after dead tissue, screwworm maggots burrow into living flesh, drilling deeper if left untreated.
The fly is attracted to any open wound, no matter how small. A scratch from playing outside, an insect bite, a small cut — any break in the skin can become an entry point.
Without treatment, infestations may become fatal within days.
Should Pet Owners Be Worried?
If you live in or near South Texas, or if your pet has recently traveled through affected areas in the Southwest, yes — you should be on alert. The current outbreak is concentrated in Zavala County, Texas, but the fly has been advancing northward from Central America and Mexico for two years.
The good news: the risk for most pet owners in the U.S. remains low right now. The federal government is actively releasing 100 million sterile flies per week in the U.S. and Mexico to suppress the population. But the situation is evolving quickly, and early awareness and prevention are your best protection.
What Are the Warning Signs in Dogs and Cats?
Screwworm infestations can look deceptively mild at first, then deteriorate fast. Check your pet regularly, especially after outdoor time, and watch for:
- A wound that seems to be getting larger rather than healing
- Unusual discharge or a foul smell coming from any wound
- Visible maggots in fur or around a wound (they’re cream-colored and small)
- Your pet scratching, biting, or licking one spot obsessively
- Fly eggs near body openings — nose, ears, eyes, or genitals
- Lethargy, loss of appetite, or behavioral changes without obvious cause
- Any wound that just “doesn’t look right”
Even tiny wounds matter. Don’t dismiss a small cut as nothing, especially if you live in or have recently visited a high-risk area.
What Should You Do If You’re Concerned?
Call your vet immediately. Don’t wait to see if it gets better. If screwworm larvae are present, hours matter.
- Tell your vet where your pet has been recently
- Don’t attempt to remove larvae yourself without guidance — improper removal can cause larvae to burrow deeper
- If you can see maggots, cover the wound loosely and get to a vet or emergency animal clinic the same day
Are There FDA-Approved Treatments for Pets?
Yes. The FDA has moved quickly to authorize treatments specifically for NWS in dogs and cats. Here’s what’s currently available:
For dogs:
- Credelio Quattro-CA1 (lotilaner, moxidectin, praziquantel, pyrantel) — conditionally approved chewable tablet for NWS treatment
- Credelio (lotilaner) chewable tablets — Emergency Use Authorization for NWS treatment in dogs and puppies
- NexGard (afoxolaner) chewable tablets — Emergency Use Authorization for NWS treatment in dogs and puppies
For cats:
- Credelio CAT (lotilaner) — Emergency Use Authorization for NWS treatment in cats and kittens
- NexGard COMBO (esafoxolaner, eprinomectin, praziquantel topical) — Emergency Use Authorization for cats and kittens
These require a veterinary prescription. Some are brands pet owners may already recognize from flea and tick prevention — but the NWS-specific authorizations are distinct, so always consult your vet rather than using products you have at home without guidance.
The FDA continues to update the approved drug list. Check the FDA’s official NWS page for veterinarians for the latest.
How to Protect Your Pet Starting Today
You don’t need to panic, but you do need to be proactive:
1. Get your pet on a flea and tick preventative. Isoxazolines such as Bravecto, Simparica, and others have demonstrated efficacy against NWS.
2. Inspect your pet after every outdoor outing. Run your hands through their coat, check ears, paws, around the mouth, and any spot they seem to be bothering. Make it part of your routine.
3. Clean and cover any wound promptly. Don’t leave open wounds unattended. Clean cuts or scrapes right away and keep them covered until healed.
4. Call your vet and ask about NWS. Even if your pet is healthy, it’s worth a conversation to understand what to watch for and what treatments your vet has access to.
5. Avoid high-risk areas if possible. If you’re in South Texas or near the border, reduce prolonged outdoor exposure in brushy, fly-heavy environments during peak fly hours (typically daytime).
6. Stay updated. The situation is changing week to week. Bookmark screwworm.gov and the FDA’s NWS page for official updates.
Is This a Food Safety Issue?
No. U.S. health officials are clear that this does not affect the safety of meat or any food product. This is an animal health issue. For pet owners, that means focusing on protecting your companion animals, not your groceries.
The Bottom Line
New World screwworm is a serious threat that’s new to this generation of American pet owners. Most of us have never encountered it, which means it’s easy to dismiss a warning sign as something minor.
Don’t. Know what to look for, check your pet regularly, and have your vet’s number ready. The parasite moves fast — but so can you.
This article is for informational purposes only and does not constitute veterinary or medical advice. Always consult a licensed veterinarian for your pet’s health concerns.
