FDA Issues Emergency Authorization for Drug to Treat New World Screwworm for Canines

New World Screwworm (NWS, Cochliomyia hominivorax) USDA.Gov

Simparica TRIO authorized for emergency treatment of New World screwworm in dogs and puppies

WASHINGTON — The U.S. Food and Drug Administration (FDA) has given veterinarians permission to use the prescription drug Simparica TRIO to treat dogs and puppies that become infested with New World screwworm, a rare but serious parasite that can cause dangerous wounds.

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Federal officials say the overall risk to pets remains low, and there have been no detections of New World screwworm anywhere in the Carolinas. The parasite has only been found in small areas of Texas and New Mexico. Even so, the FDA says this authorization helps veterinarians be ready if a case appears.

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Dogs can pick up screwworms when flies lay eggs in open wounds. The larvae then feed on the tissue, which can quickly become severe. Pet owners should watch for signs such as visible maggots or a strong, foul smell coming from a wound or from areas like the eyes, ears, nose, or mouth. Any dog showing these symptoms needs immediate veterinary care.

The USDA continues to track confirmed cases through its national dashboard, which remains the main source for updated information.

FDA officials say the emergency authorization gives veterinarians another tool if an infestation occurs. They also stress that dog owners should stay aware of the signs but not be alarmed, and talk with their veterinarian if they have concerns.

Simparica TRIO has been on the market since 2020 for heartworm, flea, and tick protection. One of its ingredients, sarolaner, belongs to a class of drugs that can occasionally cause neurologic side effects in some dogs, such as tremors or seizures. Because of this, the product is only available by prescription, and veterinarians will determine whether it is appropriate for each dog.

The FDA notes that Simparica TRIO is authorized only for treating screwworm infestations, not preventing them.