- Not a substitute for professional veterinary help.
You know that your pets need protection against parasites like fleas, ticks, and heartworms. But there’s a much more serious parasite that’s re-emerging in the US: screwworms.
New World screwworms are a type of parasitic blow fly that lay eggs in open wounds or sores on your pet’s skin. Within 24 hours, the eggs hatch into worm-like larvae and burrow into your pet’s skin, like screws into wood.
Screwworms had previously been eliminated in North America, but they’re spreading northward through Central America and Mexico. As of June 2026, they’ve been reported in animals in two Southwestern US states, Texas and New Mexico.
If you’re in an at-risk state or worried that these parasites could reach your backyard, here’s how to spot signs of screwworms and get your pet the treatment they need.
How Serious Is a Screwworm Infestation?
Unlike most fly larvae that only eat dead tissue, screwworms can infect living, healthy skin tissue, explains Dr. Rebecca Greenstein, B.Sc., D.V.M., one of Rover’s resident veterinary experts.
This means that screwworm infestations can spread quickly, making existing wounds larger, deeper, and more painful within a few days. Left unchecked, these wounds can be fatal to pets in one to two weeks, making urgent vet attention critical.
Which Pets Are at Risk of Screwworms?
Screwworms can infect any warm-blooded mammal, including dogs and cats, especially if they have an open wound.
Any pets that recently traveled from South or Central America have a higher risk factor. So do pets who live in or have recently visited affected states, like Texas or New Mexico.
As of June 2026, counties with active or inactive screwworm cases in animals include:
- Crockett, Texas
- Edwards, Texas
- Gillespie, Texas
- La Salle, Texas
- Sutton, Texas
- Terrell, Texas
- Tom Green, Texas
- Zavalla, Texas
- Lea, New Mexico
So far, there are 16 documented animal cases in the US, primarily in livestock. Only one case is confirmed in a dog, and none have been reported in cats or humans.
While humans can get screwworms, infestations are rare and aren’t contagious. They can’t spread from pets to people or pet to pet: the flies have to lay eggs directly in an open wound. You can keep an eye on current cases on the USDA’s website.
Warning Signs of a Screwworm Infestation in Pets
Look for wounds that are getting suspiciously bigger instead of healing normally, says Dr. Greenstein.
The biggest sign is the presence of screwworm larvae, which burrow in a “screw-like” spiral pattern. You might also notice the eggs, which are white and cluster along the edges of wounds.
That said, you can’t always see a screwworm infestation, since they can lodge inside your pet’s nose, ears, or mouth. More symptoms to look for include:
- Foul odor, such as decay or rot
- Blood-tinged discharge
- Head-shaking
- Signs of pain or irritation
- Behavior changes, including unusual aggression
- Lethargy or weakness
- Loss of appetite
What To Do If You Suspect Your Pet Has Screwworms
“If you even think your pet has screwworms, prompt veterinary attention is essential,” Dr. Greenstein says. Keep your pet indoors until your vet can confirm a diagnosis.
1. Seek vet treatment ASAP
Going to the vet ASAP can get your pet the medications and treatments they need to salvage damaged tissue and get on the road to healing.
In June 2026, the FDA authorized nitenpyram tablets to treat screwworms in healthy dogs and cats at least four weeks old and weighing at least two pounds. Your pet will take two doses based on their weight, with most screwworm larvae dying within hours of the first dose.
After a course of the meds, your vet may still need to manually remove the larvae still inside the skin to prevent infections.
Dr. Greenstein explains that this involves sedating your pet to remove all visible screwworms and dead tissue and disinfect the surrounding skin. Aftercare for this surgery involves pain meds, antibiotics, and a post-op wound care routine customized by your vet.
2. Call your local government health organization
If your vet confirms screwworms, they will likely take a sample and contact your local or state public health department.
Depending on your local rules, you or your family may also be required to report the screwworms to your local health organization, Dr. Greenstein explains.
3. Spread the word
Beyond telling local health organizations, you might also choose to spread the word to other pet parents by posting to local social media pages or alerting your local news.
Screwworms can’t spread from pet to pet, or from person to person. But if adult flies are in the area, other pets could be at risk, too.
How To Prevent Screwworms in Pets
While screwworms are scary and serious, the good news is that they’re also highly preventable. You can do your part to protect your pets by taking these measures.
1. Leave your pets at home when traveling
Your pet faces the highest risk of screwworms whenever they visit a place known to have active screwworm cases. Central or South America has affected countries which include but aren’t limited to:
- Belize
- Cuba
- Costa Rica
- Dominican Republic
- Guatemala
- Haiti
- Nicaragua
- El Salvador
- Mexico
In the United States, traveling to states like Texas and New Mexico with your pet may require more prep and monitoring. If your pet is prone to getting wounds—whether due to immunodeficiencies or rambunctious behaviors—consider leaving them with a sitter or boarding them instead of traveling with them.
2. Adopt locally instead of abroad
Screwworms can spread if you rescue a pet from a place with screwworms. Rescues with any open wounds, breaks in the skin, or recent surgeries are especially at risk, Dr. Greenstein explains.
If you’re actively looking for a pet to adopt and live in an area without any recent screwworm reports, consider adopting from a local pet shelter or rescue. Feeling extra cautious? You can ask the facilities whether the pet you’re interested in has traveled recently.
3. Cover and protect any open wounds
If you live in an affected area, you don’t necessarily need to keep your pets indoors. But look them over for any skin wounds daily. If you spot any open wounds, disinfect and cover them to keep flies out.
“Any break in the skin could be a vulnerability,” Dr. Greenstein says. That includes the tiniest scrapes, cuts, or even bites from mosquitoes and fleas.
4. Stay up to date on flea & tick meds
Speaking of fleas, some monthly flea and tick medications are effective against screwworms.
The FDA found that the anti-parasite medications afoxolaner (NexGard) and esafoxolaner (NexGard combo) can be effective for screwworms. You can get these medications as regular monthly anti-flea and tick medicines prescribed through your vet.
5. Stay calm and informed
While all this sounds scary, it’s important to remember that most dogs and cats in the US face a low risk of screwworms.
The adult flies can only travel 12 miles on their own, so they aren’t likely to spread rapidly. Organizations like the USDA are already working hard to stop the current outbreak.
As a concerned pet parent, the best thing you can do is stay calm, avoid taking your pet to affected areas, and offer prompt first-aid to any open wounds. Keep an eye on the screwworm spread with your local news and the USDA’s website.
