New World screwworm has now been confirmed in a dog in Arizona, the first case in the state and the third US state affected in 2026. The parasite’s larvae feed on living tissue in wounds, so any wound with maggots, a foul smell, or rapid worsening needs same-day veterinary care. Daily wound checks are the best protection.
What is New World screwworm? New World screwworm is a parasitic fly (Cochliomyia hominivorax) whose females lay eggs in open wounds or body openings. The larvae burrow into living tissue and feed for about a week. Unlike ordinary maggots, which feed mostly on dead tissue, screwworm larvae eat living flesh, so an infested wound can deepen fast and turn life-threatening without treatment. Eradicated from the US in 1966, the pest has returned in 2026.
What just happened in Arizona?
On October 28, 2026, the US Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) confirmed screwworm in a dog in Cochise County, Arizona, which borders Mexico. Samples were confirmed at the APHIS National Veterinary Services Laboratories in Ames, Iowa; the Arizona Department of Agriculture said the dog had a maggot-infested wound on its back and was receiving veterinary care.
Arizona is the third US state with cases in 2026, after Texas and New Mexico; the first US detection came on June 3, 2026, in a calf in Zavala County, Texas. Reuters reported the USDA had recorded 71 cases since June, with 18 active as of October 28, and that the agency has set up a 20-kilometre (12-mile) infested zone with movement controls, extra surveillance, and releases of sterile flies. For dog owners: this is no longer only a livestock story.
How does screwworm in dogs start?
A female screwworm fly, drawn to the smell of a wound, lays clusters of white eggs along its edges or around body openings such as the ears, nose, eyes, genitals, or navel. The larvae burrow deep and feed on living flesh for roughly seven days before dropping to the ground to pupate.
State guidance stresses that wounds as small as a tick bite can attract a screwworm fly, with infestations more likely around the face and genital area. Outdoor dogs and dogs recovering from surgery, bites, or sores carry the most risk. Screwworm is not spread between dogs by play or licking, nor through food: it starts when a fly lays eggs in a wound.
What are the warning signs of screwworm in dogs?
Check your dog’s skin daily, and harder after walks, play, and travel. Call your veterinarian promptly if you see any of these, especially in combination:
- Maggots or white egg masses in or around a wound
- A wound draining, enlarging, or suddenly deepening instead of healing
- A foul, decay-like smell coming from a wound
- Bloody discharge or pus that will not dry up
- New pain, irritability, scratching, or head shaking
- Lethargy, loss of appetite, or a dog that withdraws and hides
- Sores around the ears, nose, eyes, genitals, or navel
One caution: maggots alone do not prove screwworm. Other flies lay eggs in wounds too, but their larvae usually sit on the surface rather than burrowing deep. Only laboratory testing confirms the species, so a suspicious wound belongs in front of a veterinarian.
What should you do if you find maggots in your dog’s wound?
Act the same day. Do not wait to see if the wound improves, and do not try to treat suspected screwworm yourself:
- Call your veterinarian immediately. Describe what you found, when you noticed it, and any recent travel or time near livestock or wildlife. If your clinic is closed, call an emergency clinic.
- Keep your dog calm and protected. Prevent licking and scratching if you safely can, and keep your dog indoors and away from flies until seen.
- Do not apply insecticides, home chemicals, or unprescribed medicines. Treatment means wound cleaning and larva removal plus protection against secondary infection; your vet will choose what is safe.
- Report it through your veterinarian. Suspected cases go to your state animal health official or USDA APHIS, and your vet will know the route. Early reporting protects other animals too.
Treated promptly, infested animals can recover. Left untreated, screwworm can cause severe wounds, suffering, and death — which is why speed matters most.
How can you protect your dog from screwworm?
- Inspect your dog daily. The USDA urges owners in affected areas to check animals every day: coat, ears, belly, legs, tail base, and any old scars or sores.
- Treat every wound promptly. Cover minor scrapes where possible and get vet advice for deep, dirty, or slow-healing wounds, or wounds near the eyes, ears, or genitals.
- Cut fly exposure. Keep living areas clean, remove waste promptly, and keep dogs with open wounds indoors or protected from flies until healed.
- Check dogs after travel. Inspect dogs returning from southern border states or Mexico, and new shelter or rescue arrivals from southern regions, before mixing them with other animals.
Should dog owners outside Arizona worry?
No need to panic, but stay aware. Cases have now appeared in Texas, New Mexico, and Arizona, and the USDA updates its case dashboard at screwworm.gov daily at 6 p.m. Eastern. Dogs that travel, dogs adopted from southern shelters, and any dog with an unexplained worsening wound deserve the same careful look, wherever you live. Awareness plus a same-day vet call is the whole strategy.
For everyday health scares, try BlueTarg’s free Dog Toxin Checker and Dog Wellness Planner, and read our dog emergency evacuation plan.
Frequently asked questions about screwworm in dogs
Can screwworm in dogs be treated?
Yes, when a veterinarian treats it: wound cleaning, larva removal, and guarding against secondary infection. Same-day care gives a much better outlook than waiting while the infestation deepens.
Can humans get screwworm?
Yes, but human cases are much less common than animal cases. Even a small skin break can be an entry site. A rapidly worsening, foul-smelling wound needs prompt medical care.
Is screwworm contagious between dogs?
No, not by contact. Dogs do not pass it to each other by playing, licking, or sharing bowls. Each infestation starts when a fly lays eggs in a wound or body opening, so the risk comes from flies and open wounds, not from other dogs.
How is screwworm different from ordinary maggots?
Ordinary maggots usually feed on dead tissue on a wound’s surface. Screwworm larvae burrow deep and feed on living tissue, so infested wounds enlarge and deepen quickly and smell of decay. Only lab testing confirms the species.
Where can I check current screwworm cases?
The USDA dashboard at screwworm.gov, under “Current Status,” updates daily. Your state veterinarian’s office and your own veterinarian can also advise on local risk.
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Sources: USDA APHIS, “USDA Confirms New World Screwworm Detection in Arizona,” October 28, 2026; Oregon Department of Agriculture, New World Screwworm information for pet owners. For information only, not veterinary advice — if your dog has a suspicious wound, contact your veterinarian right away.