In June 2026, the United States confirmed its first case of New World screwworm in a dog in nearly sixty years. The infestation, in a dog whose household is in Lea County, New Mexico, arrived just days after the parasite was detected in southwest Texas for the first time since the 1960s. For most of the past year, public conversation about screwworm has centered on cattle and the food supply. The confirmed canine case changed that conversation overnight, because it confirmed what veterinarians already knew: the New World screwworm does not distinguish between livestock and pets.

The current risk to the average pet dog remains low, especially outside the affected areas of Texas and New Mexico. But screwworm infestations are painful, fast-moving, and occasionally life-threatening, and they can begin in a wound as small as a tick bite. Knowing what the parasite is, how it reaches dogs, what the earliest signs look like, and how it is prevented gives you a meaningful advantage. This guide walks through all of it, with an added note for families caring for dogs with cancer or recovering from surgery, who have specific reasons to stay alert.

In This Article

• What the New World Screwworm Actually Is
• The 2026 U.S. Outbreak: A Timeline
• How Screwworm Reaches Dogs
• Warning Signs to Watch For
• How Veterinarians Diagnose an Infestation
• Treatment Options for Dogs
• Prevention: Your Strongest Tool
• A Note for Dogs With Cancer or Healing Wounds
• Recovery and Outlook
• What This Means for Dog Owners
• Frequently Asked Questions

What the New World Screwworm Actually Is

Despite the name, the New World screwworm is not a worm. It is the larval stage (the maggot) of a parasitic fly, Cochliomyia hominivorax. The name describes the larva's behavior: it screws its way down into living flesh as it feeds.

This feeding behavior is what sets screwworm apart from the ordinary maggots most people picture. The vast majority of fly larvae are scavengers that consume dead or decaying tissue. New World screwworm larvae are obligate parasites, meaning they require living tissue to survive. They tear into healthy, living flesh with sharp paired mouth hooks, and as they burrow deeper they enlarge the wound, invite secondary bacterial infection, and attract still more flies. A wound that should be closing instead grows wider and deeper.

The life cycle is brief and efficient, which is part of what makes the parasite so dangerous:

1. Eggs. A female fly is drawn to the odor of an open wound or a moist body opening, even a very small one. She lays a tight cluster of eggs, often several hundred at a time, at the edge of the wound. Over her short life she may lay up to about 3,000 eggs.
2. Hatching. The eggs hatch into first-stage larvae within roughly 12 to 24 hours.
3. Feeding. The larvae burrow into living tissue and feed, molting through three larval stages over about five to seven days. A mature larva is roughly 15 millimeters long, pointed at the head and blunt at the tail.
4. Pupation. The fully fed larvae drop from the animal to the ground and pupate in the soil.
5. Adult emergence. Adult flies emerge anywhere from about a week to several weeks later, depending on temperature and humidity, and the cycle begins again.

Because eggs can hatch in under a day and larvae start consuming tissue almost immediately, an infestation can escalate from a barely noticeable wound to a serious one in a remarkably short time. Early intervention is everything.

The 2026 U.S. Outbreak: A Timeline

The United States eradicated screwworm in 1966 using the sterile insect technique, a program that releases millions of sterilized male flies so that wild females mate without producing offspring. It was the first pest ever controlled this way, and it kept the country essentially screwworm-free for decades, apart from isolated incursions such as a 2017 outbreak in the Florida Keys that was quickly eliminated.

The current situation traces to a northward march of the parasite that began in 2023, when an outbreak was declared in Panama and the Darien Gap, long a natural barrier, was breached. From there the fly spread through Central America, reached southern Mexico in 2024, and continued north.

The key 2026 dates so far:

• June 3, 2026: The first U.S. detection in nearly 60 years is confirmed in a three-week-old calf in Zavala County, Texas, with larvae in the umbilical area.
• June 5, 2026: A second case is confirmed in Zavala County, in a one-month-old calf a few miles from the first.
• June 8, 2026: USDA confirms several additional cases, including a goat in Gillespie County, Texas, a calf in La Salle County, Texas, and, most notably for pet owners, a dog. The canine case was first reported in Andrews County, Texas, then reclassified once investigators determined the dog lived in Lea County, New Mexico, making it that state's first case. Officials believe it may be isolated, but the dog's travel and exposure history were not fully known, so surveillance of nearby animals was expanded.
• June 11, 2026: The FDA issues an Emergency Use Authorization for a generic over-the-counter treatment for dogs and cats (more on that below).

The case count across Texas and New Mexico has continued to climb through June and is best described as a developing situation. Rather than rely on any single number that will be outdated quickly, check the USDA's live dashboard at Screwworm.gov for the current confirmed total and locations.

Inside the Canine Case

When USDA reclassified the dog's case to New Mexico, officials described it as believed to be isolated, with one important caveat: the dog's recent travel and exposure history were not fully known. That uncertainty triggered a standard set of containment steps drawn from USDA's New World Screwworm Response Playbook, carried out jointly by APHIS and New Mexico state officials. They included continuing the epidemiological investigation into how the dog became infested, sampling and inspecting the other animals in the dog's household, setting fly traps in the area, preparing for a release of sterile insects if it became necessary, and conducting local outreach to encourage reporting of any other suspect cases.

Dudley Hoskins, USDA's Under Secretary for Marketing and Regulatory Programs, called the situation evolving and pledged that the agency would share what it learns "quickly, accurately, and transparently" so that animal owners and communities can stay vigilant. The same day, USDA's National Veterinary Services Laboratories confirmed a separate case in a goat in Gillespie County, Texas.

Federal and state agencies have responded aggressively. A unified incident command with the Texas Animal Health Commission, twenty-kilometer "infested zones" around each detection with quarantines and movement controls, and renewed sterile-fly dispersal (including aerial releases that began June 9 from Moore Air Base in Edinburg, Texas) are all in motion. The food supply itself is not considered at risk; screwworm does not infest meat, produce, or other food products.

How Screwworm Reaches Dogs

Livestock are still the most commonly affected animals, but screwworm can infest essentially any warm-blooded host, including dogs, cats, wildlife, birds, and, rarely, people. In Mexico's outbreak, dogs have been the second most affected species after cattle, which is part of why the U.S. canine case drew so much attention.

The entry point is almost always a wound or a moist body opening. A female fly only needs a small target. Common points of entry in dogs include:

• Open wounds, cuts, and scrapes
• Tick and insect bites
• Hot spots and other irritated, broken skin
• Surgical incisions
• The umbilicus (navel) of newborn puppies
• Skin folds and nasal folds
• Natural openings such as the eyes, ears, nose, mouth, and genitals

Young animals are especially vulnerable, and senior dogs are at risk when a wound goes unnoticed under fur or in a skin fold. Because the adult screwworm fly looks much like an ordinary housefly (it is a metallic blue-green blowfly with reddish eyes and three dark stripes on its back, but that is hard to judge in the moment), the early stages of an infestation are easy to miss without deliberate inspection.

Human infestations are rare. Good hygiene and prompt wound care make them uncommon, but anyone who notices a suspicious, non-healing lesion, particularly after time in an affected area, should seek medical care.

Warning Signs to Watch For

If your dog has a wound of any kind, the single most useful habit is to ask one question each day: is it healing, or is it getting worse? A normal wound trends toward closing. An infested wound trends the other way.

Take your dog to a veterinarian promptly if you notice any of the following:

• A foul or unusual odor coming from a wound
• A wound that is enlarging rather than shrinking
• Excessive or bloody drainage
• Increasing swelling, redness, or irritation around the site
• Visible larvae (maggots) moving in or around the wound
• Clusters of eggs, which look like a small patch of pale, sticky grains at the wound's edge
• Restlessness, distress, or obvious pain
• Persistent licking, biting, or chewing at one spot

Screwworm infestations are intensely painful, and behavioral changes such as restlessness or fixation on a particular area can appear before the wound looks dramatic. The earlier the infestation is caught, the fewer complications your dog is likely to face.

For owners in or near affected areas, USDA has gone a step further and urged a daily inspection of every animal, looking specifically for draining or enlarging wounds, maggots or egg masses, signs of discomfort or irritability, and lesions around body openings such as the ears, nose, genital area, and umbilicus. Making this a brief daily routine, rather than waiting for a wound to look obviously wrong, is the practical core of early detection.

How Veterinarians Diagnose an Infestation

A suspected screwworm infestation is treated as an emergency. The most direct sign is seeing larvae in or around a wound. When the species is in question, a veterinarian can collect larvae (typically preserved in alcohol) and submit them for laboratory identification, which distinguishes Cochliomyia hominivorax from look-alike fly species by features such as its darkly pigmented internal breathing tubes.

Diagnosis also draws on context. Your veterinarian will ask about recent travel, the environments your dog has been in, and any exposure to livestock or wildlife, all of which help establish the likelihood of screwworm versus a more ordinary wound infestation.

Because screwworm threatens livestock and agriculture, it is a reportable condition in many situations. Your veterinarian may be required to notify state or federal animal health officials, and may recommend a period of observation. This reporting is part of the national eradication effort, not a reflection of anything you did wrong.

Treatment Options for Dogs

Treatment has three goals: kill the larvae, manage your dog's pain, and prevent or treat secondary infection. The specifics are always determined by your veterinarian based on your dog's situation, but the general approach includes the following.

Larvae removal and wound care. Visible larvae are physically removed and the wound is thoroughly cleaned. In severe cases, sedation may be needed to do this safely and humanely. Supportive care can include fluids and pain relief, and antibiotics are commonly added when secondary bacterial infection is present.

Antiparasitic medication. A central part of treatment is an antiparasitic drug. As of mid-2026, the FDA has authorized several products specifically for treating New World screwworm infestation (myiasis) in dogs, all under emergency use authorizations or conditional approvals rather than full approval:

• NexGard (afoxolaner) chewable tablets, authorized for treating screwworm larvae infestations in dogs and puppies.
• Credelio (lotilaner) chewable tablets, authorized for dogs and puppies eight weeks and older.
• Credelio Quattro (lotilaner, moxidectin, praziquantel, and pyrantel), conditionally approved as a monthly chewable for dogs and puppies at least eight weeks old and weighing at least 3.3 pounds.
• Generic nitenpyram tablets (the active ingredient also sold under brand names such as Capstar and CapAction), authorized in June 2026 as the first generic option, for dogs, puppies, cats, and kittens at least two pounds and four weeks old. These over-the-counter tablets work fast, killing most larvae within hours, with a second dose given six hours after the first. They are short-acting, so they do not prevent future infestations, and because they do not physically remove larvae, a veterinarian may still need to clean out the wound.

Several of these are familiar flea and tick medications in the isoxazoline drug class, repurposed under emergency authorization for screwworm. An important practical point: no product currently has full FDA approval for this use, so treatment should always be directed by a veterinarian who can choose the right drug, dose, and supportive care for your individual dog. In severe or neglected cases, infection can become systemic and life-threatening, which is another reason early veterinary involvement matters so much.

Prevention: Your Strongest Tool

The good news is that prevention is straightforward and largely overlaps with parasite control many dogs are already on.

Keep your dog on a year-round prescription parasite preventative. Veterinarians point to the isoxazoline class of products (which includes the active ingredients in NexGard, Credelio, and Simparica) as the single best defense. A dog on a current isoxazoline preventative is highly protected against screwworm larvae. These products do double duty: they kill the larvae directly, and by preventing flea and tick bites they reduce the scratching and small wounds that attract egg-laying flies in the first place.

Inspect your dog regularly and care for wounds promptly. Run your hands over your dog every few days, checking skin folds, ears, the area under the tail, and between the toes. Clean any wound right away, keep it covered when practical, and watch its progress. A wound that is kept clean and closed is a far less attractive target.

Be extra vigilant near affected areas. If you live in or near a county with confirmed cases, limit unnecessary outdoor exposure, monitor your dog's skin and behavior closely, and follow any additional guidance from your veterinarian.

Mind travel rules. Because screwworm spreads through animal movement, federal and state requirements for traveling with dogs have been changing quickly in 2026, including certification and inspection rules for crossing certain borders or state lines. If you plan to travel with your dog, confirm the current requirements with USDA and your destination's state animal health authority before you go. The American Kennel Club is maintaining an updated summary of interstate movement requirements that is a useful starting point.

A word of caution on home remedies: some owners ask about topical fly repellents. These can have a role, but only products labeled as safe for dogs and used exactly as directed. Many ingredients that are fine for one species are toxic to another (several are dangerous to cats), so never share products between pets, and check with your veterinarian first.

A Note for Dogs With Cancer or Healing Wounds

Families caring for a dog with cancer have a few specific reasons to pay closer attention to this parasite, and a clear-eyed understanding helps far more than worry.

Screwworm flies are drawn to exactly the kinds of wounds that cancer treatment can involve: surgical incisions from tumor removal or biopsy, ulcerated or open skin masses, and any area that is slow to heal. A dog undergoing chemotherapy may also have a somewhat blunted ability to fight off the secondary bacterial infections that screwworm wounds invite. On top of that, dogs who are unwell or less mobile may groom themselves less and may not signal discomfort as clearly, so an infestation can progress further before anyone notices.

None of this means a dog with cancer is destined to encounter screwworm, and outside the affected regions the odds remain low. What it does mean is that the basic protective steps matter even more for these dogs:

• Keep surgical sites and any open or ulcerated lesions clean, covered when possible, and checked daily.
• Stay current on a veterinarian-recommended parasite preventative unless there is a specific reason your oncology team has advised otherwise; ask them directly, since some dogs on cancer protocols have individual considerations.
• Inspect the whole dog, not just the obvious wound, on a regular schedule.
• Call your veterinary team early about any wound that smells off, drains more than expected, or stops improving.

If your dog is in active cancer treatment, coordinate parasite prevention with your oncology team rather than starting anything new on your own, so that everything works together safely.

Recovery and Outlook

Recovery depends heavily on how early the infestation is caught, where it is located, and how deep the larvae have burrowed. A case caught early, with only mild tissue damage, may heal like an ordinary small wound over a few weeks. A more advanced infestation, or one complicated by secondary infection, takes considerably longer, and deep tissue destruction can occasionally leave lasting damage. This is the practical argument for vigilance: the difference between a minor problem and a major one is often just a matter of days.

What This Means for Dog Owners

There is no need to panic. The United States has eradicated screwworm before and is mounting an aggressive, coordinated response now. The most useful posture is calm preparedness rather than fear.

For you as a dog owner, that comes down to a short list: keep your dog on a prescription parasite preventative year-round, check your dog's skin and wounds regularly, clean and monitor any wound promptly, be especially watchful if you live near an affected area or travel with your dog, and call your veterinarian early if anything looks or smells wrong. Those habits protect against far more than screwworm, and they put you well ahead of this particular parasite.

Frequently Asked Questions

Can my dog catch screwworm from another dog? Not directly. Dogs become infested when a screwworm fly lays eggs in a wound or body opening, not through contact with another infested animal. The risk comes from the environment and from flies, which is why wound care and parasite prevention are the focus.

Is my family at risk if my dog is infested? Human infestation is rare and is not caught from your dog. People become infested the same way animals do, through a fly laying eggs in a wound. Still, if you find larvae in your dog's wound, handle the situation carefully, follow your veterinarian's guidance, and seek medical care for any suspicious, non-healing wound of your own.

My dog is already on flea and tick medication. Is that enough? If it is a current, veterinarian-prescribed isoxazoline product, it offers strong protection against screwworm larvae. Confirm with your veterinarian that your dog's specific product and schedule provide this coverage, and keep it up year-round.

How worried should I be if I do not live in Texas or New Mexico? The confirmed cases so far are concentrated in southwest Texas and New Mexico, and risk falls off considerably outside the affected zones. The sensible response anywhere is the standard prevention checklist, plus extra attention if you travel to or from an affected area.

Is the food supply safe? Yes. Screwworm does not infest meat, fruits, vegetables, or other food products, and federal inspection would identify any affected animal before its products could enter commerce.

Key Takeaways

• The New World screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae feed on living tissue, not just dead tissue, which makes its wounds worsen rapidly.
• In June 2026, the U.S. confirmed its first canine case in nearly 60 years, in a dog from Lea County, New Mexico, amid a broader outbreak in southwest Texas and New Mexico.
• Dogs become infested when a fly lays eggs in a wound or body opening; even a tick bite can be an entry point.
• Early signs include a foul odor, a growing wound, heavy drainage, swelling, visible maggots, and persistent licking or pain.
• A suspected infestation is an emergency requiring immediate veterinary care.
• Year-round prescription parasite preventatives in the isoxazoline class are the strongest defense, alongside regular skin checks and prompt wound care.
• Dogs with cancer or healing surgical wounds warrant extra vigilance, coordinated with their veterinary or oncology team.

This article is for educational purposes and does not replace individualized veterinary advice. If you suspect a screwworm infestation, contact your veterinarian, your state animal health official, or USDA immediately. For the current U.S. case count and locations, see Screwworm.gov.

References

• U.S. Department of Agriculture, Animal and Plant Health Inspection Service (APHIS) news releases, June 8 and June 11, 2026: confirmation of the first canine case (Lea County, New Mexico) and the generic nitenpyram Emergency Use Authorization. aphis.usda.gov
• U.S. Food and Drug Administration, "Animal Drugs for New World Screwworm" and "New World Screwworm: Information for Veterinarians." fda.gov
• Centers for Disease Control and Prevention, "About New World Screwworm," "Clinical Overview of New World Screwworm," and DPDx laboratory identification resources. cdc.gov
• Companion Animal Parasite Council (CAPC), Cochliomyia hominivorax guidelines. capcvet.org
• American Kennel Club, "Emerging Issue: New World Screwworm" and interstate animal movement requirements. akc.org
• USDA APHIS, New World Screwworm Response Playbook (aphis.usda.gov/sites/default/files/nws-response-playbook.pdf).
• USDA, Screwworm.gov (live confirmed-detections dashboard).