New World screwworm is back in the United States, and it doesn’t only affect livestock: several dogs have been infested in New Mexico and Arizona this fall. Should you be worried about your dog?
For most dogs in the US, the risk remains low. But screwworm in dogs starts with something every owner can spot: a wound that doesn’t heal. Here’s how to recognize the signs, which dogs are most exposed and what to do if you find maggots in a wound.
What is screwworm? #
The New World screwworm (Cochliomyia hominivorax) is a fly whose larvae feed on living flesh. The female lays her eggs in an open wound or a body opening: the nose, ears, navel or genital area. According to veterinarian Barri J. Morrison on PetMD, each female lays hundreds of eggs that hatch within a day.
The larvae, or maggots, then burrow deeper into the tissue as they feed. This infestation is called myiasis. Unlike ordinary flies, which lay eggs on dead tissue, screwworm attacks healthy flesh, and the wound gets bigger every day. Left untreated, an infestation can be fatal for an animal within about 10 days, according to the USDA.
Screwworm affects all warm-blooded animals: cattle, horses, sheep, wildlife, dogs, cats and, more rarely, people.
New World screwworm in the US: where are we? #
Screwworm was eradicated from the United States in the 1960s, apart from a brief outbreak in the Florida Keys in 2016. After moving north through Central America and Mexico, it was detected again in Texas and New Mexico in June 2026.
As of early November, the USDA had confirmed more than 100 cases in animals across Texas, New Mexico and Arizona, as reported by the American Veterinary Medical Association. Most involve livestock, but dogs are among them: seven in New Mexico in October and November alone. In Arizona, the first case confirmed by USDA APHIS on October 28 was a dog in Cochise County, and a fifth case, also a dog, was reported in Graham County on November 6, with no known travel history.
The USDA publishes confirmed detections on its screwworm.gov dashboard, updated daily. Authorities are also releasing sterile flies, which mate without producing offspring, to stop the fly from spreading.
Which dogs are most at risk? #
Any dog with an open wound can attract the fly, but some situations increase the risk:
- dogs living in or traveling to affected areas: southern Texas, New Mexico, Arizona, Mexico, Central and South America;
- dogs who spend a lot of time outdoors, on a ranch or near livestock;
- dogs with a recent wound: a cut, a bite, a scratch on a wire fence;
- dogs with a recent surgical incision, after spaying or neutering, for example;
- dogs with irritated skin, scratching from fleas or an old tick bite;
- puppies, through the navel, and senior or sick dogs who groom themselves less.
Don’t forget the skin under the collar: a collar that rubs or a metal chain can create a small wound that goes unnoticed under the fur.
Screwworm symptoms in dogs #
The first signs are those of a wound that’s getting worse, not better. PetMD and the USDA list:
- a wound that doesn’t heal, gets bigger or suddenly worsens;
- swelling, redness, or a bloody or smelly discharge;
- a strong, unpleasant odor coming from a wound or a body opening;
- your dog licking, chewing or scratching the same spot over and over;
- pain when you touch the area, restlessness or irritability;
- head shaking or pawing at the face, if the ears or nose are affected;
- maggots or white egg masses visible in the wound.
In more advanced cases, a dog may lose their appetite, become lethargic or run a fever.
What to do if you find maggots in your dog’s wound #
Call your vet right away: screwworm is an emergency, and only a veterinarian can treat it.
- Don’t try to remove the maggots yourself or squeeze the wound: the larvae burrow deep and you risk leaving some behind.
- If you need to touch the area, wear disposable gloves and wash your hands afterward.
- Keep your dog away from other animals until they’ve been seen.
- If possible, take a photo of the wound to show your vet.
At the clinic, the vet removes the larvae and sends them for identification, cleans the wound and removes damaged tissue. Most dogs also need an oral medication to kill any remaining larvae. On November 3, the FDA issued an emergency use authorization for a fluralaner-based treatment for dogs and puppies, available by prescription only. Your vet will decide which treatment suits your dog.
Screwworm is a reportable pest: your vet will notify state animal health officials or the USDA, which helps stop the spread.
How to protect your dog from screwworm #
Prevention comes down to one habit: checking your dog every day, especially if you live in or are visiting an affected area.
- Inspect their body daily: look for wounds, scratches and irritated skin, and check the ears, nose, belly, navel and the skin under the collar.
- Treat every wound quickly: clean it, keep it dry and follow your vet’s instructions until it has fully healed.
- Watch surgical incisions until they’re completely closed, and stop your dog from licking them.
- Keep parasite prevention up to date: ask your vet which product to use, as some flea and tick medications are also authorized to treat screwworm.
- Secure your yard: barbed wire, sharp branches and loose metal can cause small wounds.
- Plan ahead before traveling to Mexico or Central or South America, and check your dog carefully on your return.
🐾 Know what's normal for your dog
No collar can spot a wound for you: daily checks remain the best protection. But a dog in pain often changes their habits, moving less, sleeping badly or getting restless at night. The Biotracker follows your dog's activity and sleep every day and compares them with their own usual patterns, so you notice when something changes. Combined with a quick daily check, it gives you one more reason to call your vet early.
Can humans get screwworm from their dog? #
No, not directly. Larvae don’t pass from one animal to another, or from an animal to a person: infestation only happens when a fly lays eggs in a wound. Human cases are rare, and as of early November, there had been no locally acquired human case in the US.
If you live in an affected area, the same rules apply to you as to your dog: keep any wound clean and covered, use an EPA-registered insect repellent outdoors, and see a doctor if a wound doesn’t heal.
FAQ — screwworm in dogs #
Is screwworm in dogs common in the US? #
No. Most of the more than 100 cases confirmed since June involve livestock, and the risk remains low for most dogs. Dogs living in or traveling through southern Texas, New Mexico and Arizona should still be checked every day.
What does screwworm look like on a dog? #
It usually starts as a wound that gets bigger instead of healing, with a foul smell and discharge. You may see small white or cream-colored maggots moving inside the wound, or white egg masses at its edges.
Can my dog die from screwworm? #
Yes, if the infestation isn’t treated: the larvae destroy tissue quickly. Treated quickly by a vet, a dog can recover: the first dog diagnosed in Arizona is recovering under veterinary care.
Do flea and tick treatments protect against screwworm? #
Some products in the same family as certain flea and tick treatments are authorized to treat screwworm in dogs, but none replaces a daily check of your dog’s skin. Ask your vet which prevention suits your dog and your area.
Should I report a screwworm case? #
Your vet takes care of it, but you can also contact your state animal health official or the USDA directly if you suspect an infestation in an animal.
In short #
New World screwworm is a fly whose larvae feed on living flesh, and it has been confirmed in dogs in New Mexico and Arizona this fall. The risk remains low for most dogs, but any wound that doesn’t heal, smells bad or contains maggots needs a vet the same day. Check your dog every day, treat every wound quickly, keep parasite prevention up to date and be extra careful if you live in or travel to an affected area.