The FDA Just Cleared a Monthly Chew to Treat New World Screwworm in Dogs

PARASITOLOGY  •  INDUSTRY NEWS

Simparica Trio's Emergency Use Authorization gives veterinarians a new tool against a parasite that has already forced several states to require treatment before animals cross state lines.

New World screwworm has gone from a distant headline to an active concern for veterinarians in the span of a year, and the FDA just handed the profession a new option for fighting it in dogs. On August 13, Zoetis announced that Simparica Trio, its monthly chewable for sarolaner, moxidectin, and pyrantel, received Emergency Use Authorization from the FDA for treating infestations caused by New World screwworm larvae in puppies and dogs.

The parasite behind the emergency is Cochliomyia hominivorax, a fly species whose larvae feed on living tissue. Once a wound becomes infested, the larvae keep feeding and the damage compounds quickly, causing serious pain and, if left untreated, death. It affects livestock and wildlife as readily as it affects companion animals, which is part of why the response has escalated so fast. According to APHIS data cited by Zoetis, New World screwworm's continued spread has already prompted several states to issue formal orders requiring treatment of domestic animals as a condition of cross-border movement from infested areas.

An Emergency Use Authorization is not the same thing as full FDA approval. It is a mechanism the FDA uses to authorize a medication during a declared emergency, when a product shows promise for treating or preventing a life-threatening condition but hasn't gone through the full approval process for that specific indication. Simparica Trio remains approved for its existing uses in dogs and puppies. The New World screwworm indication exists only under the EUA and only for as long as the underlying emergency declaration stays in effect.

"The Emergency Use Authorization for Simparica Trio provides an important new tool in the fight against New World screwworm, a devastating parasite that can cause severe suffering in dogs. With this milestone, Simparica Trio helps simplify parasite protection for dogs with a single monthly chew."
  Abhay Nayak, EVP and President, U.S. Commercial Operations, Zoetis

For clinics already recommending Simparica Trio for routine parasite prevention, the practical upside here is real. The product is already FDA-approved as an all-in-one monthly protection against heartworm disease, ticks, fleas, roundworms, and hookworms, and it prevents flea tapeworm infections by killing the fleas that transmit them. It's approved to kill six tick species, including the Gulf Coast tick, which is native to southern states like Texas but has been documented well beyond that range. A dog already on the chew for routine prevention doesn't need a separate product layered on top if a screwworm infestation shows up. That's a meaningful simplification for both veterinarians managing treatment protocols and pet owners trying to keep up with them.

Nayak framed the authorization as one piece of a larger response effort. “This Emergency Use Authorization for Simparica Trio builds on Zoetis' expanding, multi-species set of solutions to help address New World screwworm across both companion animals and livestock,” he said. That livestock side of the response runs through a separate product, Dectomax-CA1 Injectable, which holds conditional approval for preventing and treating New World screwworm infestations in cattle and offers protection against reinfestation for 21 days. Under its own EUA, Dectomax and Dectomax-CA1 have also been authorized for use in dairy cattle, swine, sheep, deer, and horses over one year old, depending on the specific product and species. Together, the two authorizations give Zoetis a genuinely multi-species response, which matters for a parasite that doesn't respect the line between companion animal medicine and livestock production.

REPORT EARLY, TREAT FAST

Veterinarians are the front line for catching this early. Zoetis and USDA APHIS are both encouraging any suspicious wounds, visible maggots, or signs of infestation to be reported immediately, either to a local veterinarian, a state animal health official, or directly to APHIS. Early detection matters enormously with this parasite, since the larvae keep feeding and the tissue damage keeps compounding for as long as the infestation goes unaddressed.

WHAT TO KNOW BEFORE PRESCRIBING

There are real prescribing considerations to know before reaching for Simparica Trio under this authorization. Sarolaner belongs to the isoxazoline class, and the FDA has flagged that drugs in this class have been associated with neurologic adverse reactions, including tremors, ataxia, and seizures, in dogs both with and without a prior history of neurologic disease. The product should be used with caution in dogs who have a seizure history, and its safety hasn't been evaluated in breeding, pregnant, or lactating dogs. The most commonly reported side effects in clinical trials were vomiting and diarrhea. Full prescribing information is available at SimparicaTrioPI.com, and Zoetis has published a dedicated EUA fact sheet with additional detail specific to the screwworm indication.

New World screwworm isn't a hypothetical threat anymore, and the regulatory response reflects that urgency. An EUA that arrives alongside state-level animal movement orders is a sign of how seriously this outbreak is being tracked, and it gives veterinarians one more real option to reach for if a screwworm case walks through the door.

SOURCE: ZOETIS INC., BUSINESS WIRE, AUGUST 13, 2026