Screwworm Has Reached U.S. Dogs: What to Check and Who to Call
New World screwworm crossed into the U.S. this year, and a dog was Arizona's first case. Here is where it has been found, the signs to check for, the products the FDA has authorized, and who to call, as of early November 2026.
On this page
New World screwworm, a fly whose maggots infest open wounds and body openings of living animals, reached the United States in 2026, and dogs are among the confirmed cases. USDA confirmed a dog case in Texas in June and Arizona’s first case, a dog in Cochise County, on October 28, 2026. USDA still rates the risk to animals and people in the U.S. as very low, but if you live in Texas, New Mexico or Arizona, or travel with your dog to Mexico or Central America, a quick daily check is now worth the minute it takes.
Vets call this kind of infestation myiasis. Mexico’s animal health agency, SENASICA, describes screwworm myiasis in pets as debilitating and possibly fatal, depending on how fast it is diagnosed and treated, how heavy the infestation is and where it is on the body. Caught early, it is a treatable wound problem; left alone, it is not.
Where it has been found
In the U.S. (as of October 28, 2026): 71 confirmed animal cases since June, 18 still active, in Texas, New Mexico and Arizona. The first was a calf in Zavala County, Texas, on June 3. A dog reported from Andrews County, Texas, was confirmed on June 8; early reports said it had recently been in Mexico. The first wildlife case, an elk, followed on October 21, and Arizona’s first case, a dog, on October 28. Every detection triggers a control zone of 20 km around the site, extra trapping and the release of sterile flies, which cannot reproduce. USDA’s dashboard updates daily at 6:00 p.m. Eastern.
In Mexico: from the first case in November 2024 to July 15, 2026, SENASICA recorded 33,698 cases of gusano barrenador del ganado. Dogs are the second most affected species after cattle, with about 7,400 dog cases (my sum of the agency’s regional tables), most of them in the south. Earlier in 2026 the most dog cases were in Chiapas, Yucatán, Oaxaca, Veracruz and Campeche.
Elsewhere: USDA also lists cases in Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua and Panama. Pets coming into the U.S. from these countries must meet USDA and CDC import requirements.
What to check, and how often
If you’re in or near an affected area, look your dog over once a day. USDA’s list of signs:
- Wounds that drain or keep getting bigger, even small ones.
- Maggots or egg masses in a wound.
- Discomfort or irritability, a dog that keeps licking, chewing or scratching at one spot.
- Sores around body openings: the ears, nose, genital area and navel.
SENASICA adds bloody discharge, wounds that won’t close, a feeling of movement in the wound and a foul smell. Because the fly lays its eggs in open wounds, getting every cut, scrape or surgical site looked after promptly is part of prevention too.
If you find something
Call your vet right away. Don’t try to pull larvae out or treat the wound with home products: SENASICA’s guidance is that all treatment should be recommended and supervised by a veterinarian.
Report it. USDA asks anyone who suspects an infestation to contact a veterinarian, their state animal health official or USDA right away. In Mexico, SENASICA takes reports at 800 751 2100, on WhatsApp at 55 3996 4462 and by email at gestioncpa.dgsa@senasica.gob.mx, according to its official releases.
The products the FDA has authorized for dogs
Because screwworm was approaching, the FDA moved quickly. As of September 3, 2026, it had issued 15 emergency use authorizations and 3 conditional approvals across all species. For dogs:
| Date | Product | What for |
|---|---|---|
| Oct 24, 2025 | Credelio (lotilaner), prescription | Emergency authorization to treat infestations in dogs and puppies |
| Dec 17, 2025 | Credelio Quattro-CA1, prescription | Conditional approval to treat it in dogs and puppies at least 8 weeks old and 3.3 lb |
| Feb 18, 2026 | NexGard (afoxolaner), prescription | Emergency authorization to treat it in dogs and puppies |
| Aug 13, 2026 | Simparica TRIO, prescription | Emergency authorization to treat it in dogs and puppies |
| Sep 3, 2026 | Capstar and generic nitenpyram, over the counter | The first authorization to prevent as well as treat, in dogs and cats at least 2 lb and 4 weeks old |
Two cautions from the FDA itself. Emergency authorizations only require that a product may be effective, which is a lower bar than full approval; no drug is fully approved for screwworm yet. And the isoxazoline drugs on this list (lotilaner, afoxolaner and relatives) have been associated with neurologic reactions, including muscle tremors, wobbliness and seizures, so they’re a conversation with your vet, not something to start on your own. The FDA also asks that these drugs be used judiciously, to slow resistance.
Keeping it in proportion
Much of the news coverage calls screwworm a “flesh-eating parasite,” and the pictures are hard to look at. The facts are steadier: USDA rates the current U.S. risk as very low, and the FDA says most U.S. pets are at low risk. If you live far from the border and aren’t traveling south, a regular look-over is enough. If you’re in Texas, New Mexico or Arizona, or heading to Mexico or Central America, make the daily check a habit, keep a first aid checklist handy, and note anything odd on a symptom log so your vet gets a clear picture fast.
Frequently asked questions
- Is screwworm in the United States?
- Yes. USDA confirmed the first U.S. case in June 2026, and by October 28, 2026 there had been 71 confirmed animal cases in Texas, New Mexico and Arizona, 18 of them active. Arizona's first case was a dog. USDA still describes the risk to animals and people in the U.S. as very low, and its public dashboard is updated daily.
- What does screwworm look like on a dog?
- USDA lists draining or enlarging wounds, maggots or egg masses in a wound, signs of discomfort or irritability, and sores around the ears, nose, genital area or navel. Mexico's SENASICA adds bloody discharge, wounds that won't close and a foul smell. Any of these is a reason to call your vet right away.
- Is there a preventive for dogs?
- On September 3, 2026, the FDA issued emergency use authorizations for nitenpyram tablets (Capstar and a generic) to prevent and treat screwworm in dogs and cats that weigh at least 2 lb and are at least 4 weeks old. Several prescription products are authorized for treatment. These are emergency authorizations, not full approvals, so ask your vet which, if any, fits your dog.
- Can people catch screwworm from a dog?
- Screwworm is spread by the fly, which lays eggs in open wounds of people and animals. As of the CDC's October 22, 2026 update there had been no human cases acquired in the U.S. If your dog is infested, let your vet handle the wound and keep your own cuts covered.
Educational content only — not veterinary or professional behavior advice. Consult your vet, or a certified trainer or behaviorist, for your pet. Read the full disclaimer →
