The U.S. Food and Drug Administration has authorized the use of an existing prescription flea and tick medication to treat New World screwworm in dogs and puppies, adding a veterinary tool against a parasitic fly larva that federal officials have so far managed to contain in parts of Texas and New Mexico.
The Emergency Use Authorization (EUA) covers Simparica TRIO, a chewable tablet containing sarolaner, moxidectin, and pyrantel, already approved since 2020 for heartworm, flea, and tick prevention. It is now authorized specifically for treating active screwworm infestations, known as myiasis, in dogs that live in, travel to, or return from areas where the parasite has been detected by state or federal animal health officials, as well as certain countries south of the U.S. border. The drug is not authorized for prevention.
New World screwworm is a parasitic fly larva that burrows into the living tissue of warm-blooded animals. Signs of infestation include visible maggots or foul-smelling wounds and body openings such as the eyes, ears, nose, or mouth. Dogs showing these symptoms should receive immediate veterinary care, according to the FDA.
Most dogs in the United States face low risk of exposure because of their geographic location, but the agency said pet owners in or near affected regions should stay alert. “We want dog owners to be informed, not alarmed,” said Timothy Schell, Ph.D., director of the FDA’s Center for Veterinary Medicine. “The best thing dog owners can do right now is stay aware of the situation, know the signs of infestation, and have a conversation with their veterinarian if they have concerns.”
Simparica TRIO’s active ingredient sarolaner belongs to a class of antiparasitic drugs called isoxazolines. The products are widely used and considered safe for most dogs, but they have been associated with neurologic adverse reactions including muscle tremors, loss of coordination, and seizures. Because monitoring for and responding to these reactions requires professional expertise, Simparica TRIO remains available only by prescription.
“The FDA continues to authorize products to give veterinarians and pet owners multiple treatment options, in the unlikely event animals under their care become infested with New World screwworm,” said Acting FDA Commissioner Kyle Diamantas, J.D. “To date, the U.S. has been successful in containing the spread of NWS. We are hopeful it will remain that way.”
The FDA said the totality of available scientific evidence supports a reasonable belief that Simparica TRIO may be effective for this use and that its benefits outweigh its risks. The EUA will remain in effect until it is revoked or the HHS Secretary ends the underlying public health emergency declaration. Detailed product information is available in the Fact Sheet for Veterinarians. Simparica TRIO is sponsored by Zoetis Inc., based in Kalamazoo, Michigan.
Source: FDA Press Announcement
