A parasite the United States spent decades keeping out has turned up in an Arizona dog. On October 28, the U.S. Department of Agriculture confirmed the state's first case of New World screwworm in a dog in Cochise County, near the southern border. It is the first time the flesh-eating pest has been detected in Arizona, and it pushes a northward-creeping outbreak into a third state.
The good news first: the dog is under veterinary care, federal health officials say the overall risk to people and pets across the country remains very low, and this is a problem with a known playbook. But if you share your life with a dog, this is a story worth understanding, because the single most important defense against screwworm is an owner who knows what to look for.
What happened in Arizona
According to the Arizona Department of Agriculture, a Cochise County veterinarian examined a dog on the evening of October 26 and found a prominent wound on the animal's back that was heavily infested with maggots showing the classic markers of New World screwworm. Diagnostic samples were sent to the APHIS National Veterinary Services Laboratories in Ames, Iowa, where testing confirmed the parasite two days later.
Cochise County sits along a busy stretch of the Arizona-Mexico border and the I-10 livestock corridor, which is part of why officials moved quickly. USDA's Animal and Plant Health Inspection Service (APHIS) is working with the state on a joint containment response that follows the agency's standard screwworm playbook: a roughly 20-kilometer "infested zone" around the detection site, animal movement controls within that zone, expanded surveillance and fly trapping, and the release of sterile flies to collapse the local population. Officials have not released the dog's exact location or how it was likely exposed.
What New World screwworm actually is
New World screwworm (Cochliomyia hominivorax — the species name literally means "man-eater") is a parasitic fly, and it earns its reputation. Unlike ordinary maggots that feed on dead tissue, screwworm females lay their eggs at the edge of an open wound, a scratch, a tick bite, or even a moist body opening like the nose, ears, or eyes. When the larvae hatch, they burrow into living flesh with tiny hooked mouths, screwing themselves deeper as they feed. A single wound can attract more flies, and an untreated infestation can become life-threatening for a dog depending on its location and severity.
This is exactly why the pest was such a scourge for American ranchers and pet owners through the mid-20th century, and why its return is being taken so seriously. The U.S. eradicated screwworm in 1966 using the sterile insect technique — mass-rearing male flies, sterilizing them with radiation, and releasing them so wild females mate without producing offspring. That program, run jointly with countries to the south, held a biological barrier in Panama for decades. The current outbreak represents a breach of that line.
How big is the outbreak?
The first domestic case of this outbreak was confirmed on June 3, 2026, in a calf in Zavala County, Texas. From there it spread through South Texas and into New Mexico. By July 23, USDA had confirmed 42 U.S. animal cases — 21 in cattle, 13 in sheep, 5 in goats, and 3 in dogs — across 16 Texas counties and one New Mexico county. The count has continued to climb through the fall, and the Arizona detection marks the outbreak's first jump to a third state.
Because the numbers change frequently, USDA maintains a public dashboard at screwworm.gov that is updated regularly with confirmed detections. Most cases so far have been in livestock, which is why much of the coverage frames screwworm as a threat to the roughly $113-billion U.S. cattle industry. But dogs are clearly susceptible, and companion animals that roam, hunt, or travel near the border deserve the same vigilance ranchers are giving their herds.
Signs to watch for in your dog
Screwworm infestations, a form of myiasis, usually start at a break in the skin. The warning signs are often visible to an attentive owner:
- A wound that seems to grow larger, deeper, or won't heal normally
- Visible maggots or cream-colored egg masses in or around a wound
- A foul or unusual odor coming from a sore
- Bloody or draining discharge
- Restlessness, head-shaking, or signs of pain and irritation
- Lesions around body openings — the ears, nose, eyes, genitals, or any recent surgical or bite site
Even very small wounds matter. A nicked ear, a cracked footpad, a tick-bite scab, or a spot from a recent spay or neuter can all become entry points, so a quick daily once-over is the best habit you can build right now.
How to protect your dog
You do not need to panic, and you do not need to keep your dog indoors forever. A few sensible steps go a long way, especially if you live in or travel through the Southwest.
Check wounds daily and keep them clean
Run your hands over your dog after outdoor time, paying attention to the ears, face, paws, and any existing cuts or hot spots. Clean and cover fresh wounds promptly, and don't let a minor scrape go unwatched.
Stay current on parasite prevention
Dogs with outdoor access should be on year-round external-parasite prevention, and this outbreak is a good reminder to confirm your dog isn't overdue. If you're not sure what your dog is covered for, your vet can sort it out in a single visit. (For more on staying ahead of seasonal pet-health hazards, see our recent coverage of product and poisoning alerts.)
Be extra careful near the border and when traveling
If you live in an affected county or plan to travel with your dog to or from Mexico or Latin America, ask your veterinarian whether any pre-travel treatment is advisable and inspect your dog carefully on the way home. Federal officials specifically flag travelers and animals moving out of infested areas as higher-risk.
What to do if you suspect screwworm
If you find maggots in a wound, do not try to dig them out yourself. Removing larvae at home often leaves some behind and can make it harder for a veterinarian to confirm the diagnosis. Instead, contact your vet immediately — screwworm is a federally reportable pest, which means suspected cases are reported to state animal-health officials and USDA, and your vet knows exactly who to call. Treatment typically involves veterinarian-prescribed parasiticides, thorough wound care, and a recheck to confirm every larva is gone. The FDA has authorized several lotilaner-based products for emergency use against screwworm in dogs and cats, so effective tools exist; the key is getting your dog in front of a professional fast.
It's also worth keeping the risk in perspective. The CDC says the current risk to the public and to animals in the United States remains very low, and there have been no reports of locally acquired human infestations. Screwworm is serious, but it is also treatable and, historically, beatable — the response now underway is the same strategy that wiped the pest out of this country once before.
The bottom line for dog owners
Arizona's first case doesn't mean screwworm is coming for your backyard, especially if you live far from the border. What it does mean is that the most old-fashioned pet-care habit there is — actually looking at your dog's skin — has quietly become one of the most useful. A thirty-second wound check during tonight's belly rub costs you nothing and catches the thing that matters most.
At Sidewalk Dog, we'll keep tracking this outbreak and the guidance that comes with it. Bookmark sidewalkdog.com and sign up for our newsletter so the next health alert that affects your dog lands in your inbox before it lands in your yard.
