FDA Authorizes Drugs to Prevent and Treat New World Screwworm in Dogs and Cats
The U.S. Food and Drug Administration has expanded emergency access to two oral medications that can be used against New World screwworm in dogs and cats, giving pet owners and veterinarians a new option for preventing infestations as well as treating them.
On September 3, 2026, the FDA issued an Emergency Use Authorization for Capstar, which contains the active ingredient nitenpyram, and revised its previous authorization for generic Nitenpyram Tablets. The updated authorizations allow both products to be used for the prevention and treatment of New World screwworm infestations in eligible dogs and cats.
The development is significant because previous FDA authorizations had focused on treating existing infestations. The September action adds prevention to the authorized emergency use of these products.
What Is New World Screwworm?
New World screwworm, scientifically known as Cochliomyia hominivorax, is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals.
Unlike fly larvae that generally feed on already-dead tissue, New World screwworm larvae can burrow into healthy living flesh. Female flies are attracted to wounds and openings in the body, where they can deposit eggs. The eggs hatch into larvae that begin feeding on tissue.
Even relatively small wounds can provide an entry point. According to the Centers for Disease Control and Prevention, New World screwworm flies can be attracted to injuries as small as a scratch or tick bite. Infestations can also occur around the eyes, ears, nose and mouth.
As larvae develop, wounds can become increasingly painful, swollen and foul-smelling. Bleeding and secondary bacterial infections may also occur. Severe untreated infestations can cause extensive tissue damage and may be fatal.
What Did the FDA Authorize?
The FDA's September 3 announcement covers Capstar nitenpyram tablets and generic Nitenpyram Tablets.
The products are authorized for emergency use in dogs, puppies, cats and kittens that:
- Weigh at least 2 pounds
- Are at least 4 weeks old
- Require prevention or treatment of New World screwworm infestation
The FDA states that Capstar tablets are available in 11.4 mg and 57 mg strengths. The appropriate administration is based on the animal's weight and the specific emergency authorization.
Importantly, pet owners should understand the distinction between an FDA-approved product and an FDA Emergency Use Authorization. Capstar is an approved animal drug for other uses, but its use for New World screwworm is authorized under the emergency authorization.
The generic nitenpyram product was first authorized by the FDA in June 2026 for treatment of New World screwworm. The latest action expands its emergency authorization to include prevention as well.
Why Prevention Matters
Treating an infestation after larvae have entered an animal's tissue is an urgent situation. Prevention could be particularly valuable for pets traveling to or living in areas where New World screwworm has been identified.
The FDA says most dogs and cats in the United States currently face a low risk because confirmed infestations are geographically limited. However, animals that live in, travel to or return from affected areas may have a greater risk of exposure. Pets traveling to certain countries south of the United States may also require additional precautions.
The availability of an authorized preventive treatment gives veterinarians another tool to consider when managing pets that may be exposed.
That does not mean every dog or cat needs the medication. Pet owners should discuss the risk with a veterinarian, particularly before traveling with an animal to an affected region.
What Should Pet Owners Look For?
Early recognition can make an important difference.
Pet owners should regularly inspect animals for wounds, particularly after outdoor activities or travel. According to federal health guidance, warning signs can include visible larvae, worsening wounds, bleeding and an unusual or foul odor.
Larvae may be visible in wounds or around body openings such as the eyes, ears, nose and mouth. A wound that appears to be getting worse instead of healing should also receive prompt veterinary attention.
If a pet shows signs consistent with New World screwworm, owners should contact a veterinarian immediately rather than attempting to manage a suspected infestation at home.
Veterinary professionals can determine whether an infestation is present and whether emergency treatment or additional measures are required.
New World Screwworm Remains a Broader Animal Health Concern
The FDA's latest authorization is part of a wider federal response to the re-emergence of New World screwworm.
The agency says it had issued 15 Emergency Use Authorizations and three conditional approvals for animal drugs against New World screwworm as of September 3, 2026. These products cover different species and uses as federal and state officials work to address the threat.
The parasite is capable of affecting livestock, pets, wildlife and, in rare circumstances, people. Livestock infestations can have serious consequences for animal health and agriculture, making surveillance and rapid response important components of containment efforts.
The CDC notes that New World screwworm has historically been associated with tropical and subtropical regions of the Americas. Its recent movement northward through Central America and Mexico has increased concern about potential exposure in animals and people.
What This Means for Dog and Cat Owners
The new authorization does not mean New World screwworm is suddenly a widespread threat to pets across the United States. Federal guidance continues to indicate that most dogs and cats in the country are at relatively low risk based on geography.
However, the situation can change as the parasite is detected in new areas.
Owners who travel with pets should pay attention to official animal health advisories and discuss preventive measures with a veterinarian when visiting an affected region. Keeping wounds clean and monitoring an animal after travel or outdoor exposure can also help identify problems early.
Most importantly, pet owners should not assume that an over-the-counter medication is appropriate simply because it is accessible without a prescription. The FDA's emergency authorization includes specific eligibility requirements and limitations. Veterinary guidance is particularly important for animals that are very young, underweight, sick or potentially already infested.
A New Tool in the Fight Against Screwworm
The FDA's September 2026 action represents an important expansion of available tools for protecting companion animals from New World screwworm.
By authorizing emergency use of Capstar and expanding the authorization for generic nitenpyram to include prevention, federal regulators have addressed a gap that previously existed between treating an infestation and trying to prevent one.
For pet owners, the most important takeaway is awareness. Know whether your destination has reported New World screwworm, inspect pets for wounds after exposure, recognize the warning signs and seek veterinary care quickly if an infestation is suspected.
The new medications provide another option, but they are part of a broader strategy that includes surveillance, veterinary care and efforts by federal and state animal health authorities to contain the parasite.
Sources
- U.S. Food and Drug Administration, “FDA Issues Emergency Use Authorization for Drugs to Prevent and Treat New World Screwworm in Dogs and Cats,” September 3, 2026.
- U.S. Food and Drug Administration, “Animal Drugs for New World Screwworm.”
- Centers for Disease Control and Prevention, “Clinical Overview of New World Screwworm.”
- Centers for Disease Control and Prevention, “About New World Screwworm.”
- U.S. Food and Drug Administration, “FDA Issues Emergency Use Authorization for Generic Over-the-Counter Drug to Treat New World Screwworm in Dogs and Cats,” June 11, 2026.
Disclaimer
This article is intended for general informational purposes only and is not veterinary or medical advice. FDA Emergency Use Authorizations have specific conditions and limitations. Pet owners should consult a licensed veterinarian before using medication to prevent or treat New World screwworm, particularly if an animal is showing signs of infestation. Always follow the current FDA authorization, product information and veterinary instructions.