New World Screwworm Has Reached the US: What Dog Owners Need to Know Right Now

There is a parasite making headlines right now that every dog owner in the country should know about, whether you live in Texas, Illinois, or anywhere in between.

It is called the New World screwworm, and on June 3, 2026, the USDA confirmed it had reached US soil for the first time in nearly 60 years, identified in a calf in South Texas. Within days, additional cases were confirmed in livestock across Texas and in a dog in Lea County, New Mexico (USDA APHIS, June 2026). The situation is still developing, government agencies are actively responding, and while the risk to most pet owners outside the immediate affected region remains low, the information below is worth knowing now rather than later.

Here is a clear, calm breakdown of what this parasite is, what it does to dogs, how to recognize it, and exactly what to do if you are concerned.

What Is the New World Screwworm?

The New World screwworm, scientific name Cochliomyia hominivorax, is a parasitic fly native to South America and the Caribbean. Its name comes from the larval stage, which is where the danger lies. The adult fly itself looks unremarkable, similar to a common green bottle fly. What it does next is not.

Female screwworm flies are drawn to the scent of open wounds on warm-blooded animals. They lay hundreds of eggs directly in or near those wounds, and within 24 hours the eggs hatch into larvae that use rows of sharp, hooked barbs to burrow and spin into living tissue, feeding on the flesh of a still-living host (CDC). The infestation is called myiasis, and if left untreated it enlarges the wound, introduces deadly bacterial infections, and can kill an animal within weeks.

As the National Cattlemen's Beef Association put it, the larva does exactly what the name suggests: it screws or bores into living flesh. It is, by any honest description, a serious parasite.

The United States eradicated the screwworm in 1966 using a now-famous sterile fly technique, releasing sterile male flies to mate with wild females and collapse the reproductive cycle. Mexico followed suit by 1991. But in 2023, cases exploded in Panama, and the parasite has been advancing steadily northward through Central America and Mexico ever since (BBC). By June 2026, it crossed into US livestock for the first time in six decades.

How Did It Get Here and How Serious Is the Threat?

The screwworm's northward advance has been tracked closely since late 2024, when Mexico confirmed its first new case. Since then, it moved through Guatemala, Belize, El Salvador, Honduras, Costa Rica, Nicaragua, and into northern Mexico. By the time it reached the US border region, government agencies on both sides had been preparing containment responses for months.

As of June 11, 2026, the USDA has confirmed six cases in the US: five in Texas across Gillespie, Zavala, and La Salle counties, involving calves and a goat, and one in a dog in New Mexico's Lea County (Newsweek, June 2026). The USDA has established a quarantine zone roughly 12 miles around the initial Texas detection site and is actively dropping sterile flies across south Texas to disrupt the screwworm's reproductive cycle. A $750 million fly production facility is under construction in Texas and expected to open next year (CNN, June 2026).

For context on why this is being treated as a major agricultural emergency: a 1972 outbreak reached 90,000 cases, and the Federal Reserve Bank of Dallas has estimated that an outbreak of that scale in the Southwest alone could cost more than $3 billion (CNN, June 2026).

For most dog owners outside the immediate affected counties, current risk is low. But the situation is evolving quickly, and awareness matters.

Can Dogs Get Screwworm?

Yes. While the screwworm primarily targets livestock, all warm-blooded animals are at risk, including dogs, cats, horses, sheep, wildlife, and in rare cases, humans (PetMD, June 2026).

A confirmed case has already been identified in a dog in New Mexico. Dogs with open wounds, recent surgical incisions, skin injuries, or conditions that cause skin breakdown are at the highest risk. The fly is attracted to any opening, including wounds as small as a tick bite. Beyond wounds, screwworm flies can also lay eggs in mucous membranes, specifically ears, eyes, nose, mouth, and the genital and anal areas.

Dogs that spend significant time outdoors, especially in or near affected areas, warrant the closest attention.

What Are the Symptoms of Screwworm in Dogs?

Catching this early is critical. Symptoms to watch for include:

• A wound that is not healing or is getting worse despite care
• A wound with a foul, unusually strong odor
• Visible movement inside or around a wound (this is the larvae)
• Small, cream-colored maggots visible in or near a wound
• Excessive licking, scratching, or pawing at a wound or body opening
• Fever, lethargy, or sudden loss of energy
• Loss of appetite or sudden weight loss
• Swelling, redness, or unusual discharge around a wound site

The Animal Medical Center in New York notes that skin folds around the face, eyes, and neck; the ears and mouth; genital and anal areas; nails and paws; and any recent surgical site are the locations most worth monitoring closely (AMC, June 2026).

One important distinction: not all maggots are New World screwworm. Ordinary fly strike, called myiasis, does occur in dogs with untreated wounds. But as the Animal Medical Center emphasizes, all maggot infections require immediate veterinary care regardless of species, and any case in an affected area should be reported to authorities.

What Should You Do If You Find a Suspicious Wound?

Do not wait and watch. This is not a situation where monitoring at home for a few days is the right call. If you find a wound on your dog that looks suspicious, has maggots present, smells unusually foul, or is not improving, contact your veterinarian the same day.

According to Texas Standard, treatment generally involves removal of the larvae and thorough cleaning of the wound. The FDA has issued emergency use authorizations for several drugs to treat New World screwworm in dogs and cats, including NexGard, NexGard COMBO, and Credelio Quattro, which many veterinarians already have on hand from standard parasite prevention protocols (FDA, June 2026).

If your veterinarian suspects New World screwworm specifically, they are required to report it. You can also contact the Texas Animal Health Commission at 800-550-8242 or reach your state's USDA area veterinarian in charge. If you can safely take photos of the wound, eggs, or larvae without putting yourself at risk, those photos can meaningfully help authorities track the spread.

Screwworm is not contagious between animals or between animals and people. It cannot spread from one dog to another. The risk comes from fly exposure to open wounds, not from contact with an infected animal (Texas Standard, June 2026).

How to Protect Your Dog

Keep wounds clean and covered. Any open wound is a potential entry point. Clean cuts, scrapes, surgical sites, and skin injuries promptly. Keep them covered when your dog is outdoors, especially in areas with confirmed screwworm activity.

Stay current on parasite prevention. Veterinary experts at dvm360 note that isoxazoline products, the class of medications many dogs already take for fleas, ticks, and heartworm prevention, also provide protection against screwworm larvae. Keeping your dog on year-round ectoparasite prevention is the most straightforward protective step you can take (dvm360, June 2026).

Control tick exposure. The USDA specifically notes that protecting pets from other wound-causing parasites like ticks reduces screwworm risk, because small tick bite wounds can attract screwworm flies in affected areas (USDA APHIS). This is another strong reason to prioritize tick prevention throughout the season.

Be aware if you are traveling. If you are traveling with your dog to Texas, New Mexico, or any area near the affected counties, or if you are traveling internationally to Central America, South America, or the Caribbean, talk to your vet before the trip. The USDA has specific guidance for veterinarians whose clients are traveling with pets to endemic regions.

Watch and report. If you are in or near an affected area, inspect your dog daily. Any suspect wound or maggot infestation should be reported immediately to your state animal health official and the nearest USDA APHIS office to allow rapid response before a population can establish.

Should Dog Owners Outside Texas and New Mexico Be Concerned?

Right now, the confirmed cases are concentrated in south Texas and southern New Mexico. For dog owners across the rest of the country, including Illinois and states far from the current outbreak zone, immediate risk is very low. The situation is being actively managed by the USDA and state agricultural agencies, and containment efforts are underway.

That said, this is a developing situation. The screwworm moved from Panama to the US border in roughly three years. Staying informed through official sources like screwworm.gov and the CDC's situation summary page is a straightforward way to track any changes without relying on news cycle noise.

The bottom line from veterinary experts is consistent: do not panic, but do stay aware. Keep your dog on preventive care, tend to wounds promptly, and call your vet for anything suspicious.

Staying Ahead of What Affects Your Dog

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