Recent reports about New World Screwworm (NWS) have many pet owners concerned. While it's important to be aware of this parasite, there's no need to panic.
Unlike an infectious disease, New World Screwworm is an insect infestation. The larvae (maggots) feed on living tissue, typically entering through an existing wound. When identified and treated early, affected animals often recover well.
As experts from Texas A&M College of Veterinary Medicine note:
"Because this is not a disease — it is an insect infestation — when the insects are removed, the animal typically recovers, especially if attention is given early."
Early Detection Is Key
Pet owners should become familiar with the signs of a potential infestation, especially if their pets spend time outdoors or have wounds that are healing.
Watch for:
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Visible larvae in or around a wound
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Wounds that appear to worsen rapidly
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A foul odor, often described as decaying tissue
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Swelling, redness, or irritation around a wound
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Excessive licking or discomfort at a wound site
Common-Sense Prevention Strategies
The best defense against New World Screwworm is routine observation and prompt wound care.
Consider these preventive measures:
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Check your pets regularly for cuts, scrapes, or skin injuries.
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Clean and care for wounds promptly.
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Monitor surgical incisions and healing wounds closely.
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Maintain regular veterinary wellness visits.
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Seek veterinary attention if a wound appears unusual, worsens quickly, or develops an odor.
Source: Texas A&M College of Veterinary Medicine
What About Medications?
Currently, there are no pharmaceutical products specifically approved for the prevention of New World Screwworm infestations in dogs and cats.
Several antiparasitic medications have demonstrated effectiveness for treatment, particularly products within the isoxazoline class. Credelio Quattro is the only drug with conditional FDA approval for treatment of NWS in dogs. The following have been granted Emergency Use Authorization for treatment:
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Credelio (Lotilaner): dogs and cats
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NexGard (Afoxolaner): dogs
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NexGard COMBO (esafoxolaner, eprinomectin, praziquantel): cats
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Nitenpyram Tablets (nitenpyram): dogs and cats
However, Dr. Judy does not recommend routine use of isoxazoline medications because of concerns regarding potential neurologic side effects. Injectable ivermectin has been granted emergency use authorization for treatment of NWS in cattle, but not dogs and cats. Dr. Judy notes that “Ivermectin at higher doses is very effective. It would have to be prescribed by a veterinarian, but in my opinion, it is MUCH safer than the isoxazolines.” Veterinarians may prescribe FDA-approved products for uses that are not on the label, in accordance with the existing regulations (21 CFR Part 530) including a valid veterinarian/client/patient relationship. Always work with your veterinarian to determine the most appropriate treatment for your individual pet.
Important Note About Heartworm Preventives
Many pet owners assume that routine parasite prevention products may also protect against New World Screwworm. Unfortunately, that may not be the case.
Veterinary parasitology experts note that medications such as ivermectin, moxidectin, milbemycin, and selamectin are used at much lower doses in common heartworm prevention products than the doses studied for New World Screwworm prevention or treatment in livestock. Therefore, pets receiving standard heartworm preventives should not be assumed to have protection against New World Screwworm.
Likewise, products containing imidacloprid, including some flea and tick treatments, are not expected to provide meaningful protection because the drug primarily concentrates in the skin rather than the tissues where screwworm larvae develop.
Source: Worms & Germs Blog, June 2026
A Note on Nitenpyram (Capstar)
Nitenpyram, the active ingredient in products such as Capstar®, has been authorized for emergency use in the treatment of New World Screwworm.
One reason some veterinarians appreciate nitenpyram is that it is rapidly cleared from the body, with activity lasting approximately 24 hours. As with any medication, treatment decisions should be made in consultation with a veterinarian based on the individual pet's condition and risk factors.
The Bottom Line
The most effective protection against New World Screwworm starts with vigilance. Regularly checking your pet for wounds, providing prompt wound care, and seeking veterinary attention when something doesn't look right can go a long way toward preventing serious complications.
Awareness—not fear—is the best tool pet owners have.
Disclaimer: This content is for informational purposes only and is not meant to diagnose, treat, or replace consulting a primary veterinarian for individualized care.