FDA issues four emergency authorisations for screwworm animal drugs

The Food and Drug Administration has announced four emergency use authorisations for veterinary products to prevent or treat New World screwworm, a flesh-feeding parasite whose larvae burrow into the living tissue of warm-blooded animals [s1]. The authorisations, published in the Federal Register on 15 October 2026, are the agency's first use of its emergency powers for animal drugs against the pest [s1].

What was authorised

New World screwworm is the larval stage of the fly Cochliomyia hominivorax. When the fly lays eggs in a wound, the hatching maggots feed on live flesh, producing an infestation known as myiasis that can kill an untreated animal [s1]. The four authorisations each cover a different product and use [s1].

The FDA issued an authorisation to Elanco US Inc. on 7 August 2026 for CLiK Extra, a dicyclanil topical suspension used as a wound spray to prevent infestation in sheep, cattle, goats, swine, camelids, and several wildlife species including deer, American bison, bighorn sheep and Sonoran pronghorn [s1]. It authorised Zoetis Inc. on 13 August 2026 for Simparica Trio, a chewable tablet combining sarolaner, moxidectin and pyrantel, to treat infestation in dogs and puppies [s1]. On 27 August 2026 it authorised Bimeda Animal Health Ltd. for Bimectin, an ivermectin injection, to prevent infestation in cattle [s1]. And on 3 September 2026 it authorised Sergeant's Pet Care Products LLC for Capstar, a nitenpyram tablet, to treat and prevent infestation in dogs, puppies, cats and kittens weighing at least two pounds and aged four weeks or older [s1].

The legal mechanism

The authorisations rest on section 564 of the Federal Food, Drug, and Cosmetic Act, the same emergency-use power the agency more often invokes for human medical products during a crisis [s1]. That power lets the FDA permit the use of an unapproved product, or an unapproved use of an approved product, when there are no adequate approved alternatives available [s1].

Before such an authorisation can be issued, the Secretary of Health and Human Services must declare that circumstances justify it. On 18 August 2025 the Secretary determined that there was "a significant potential for a public health emergency that has a significant potential to affect national security or the health and security of U.S. citizens living abroad" and that involved screwworm, and declared the same day that the circumstances justified authorising emergency use of animal drugs against it [s1][s2]. Notice of that declaration appeared in the Federal Register in August 2025 [s2]. The four product authorisations announced this month are the practical result of that declaration, more than a year later [s1].

Why a parasite reached this threshold

The emergency framing turns on the parasite's history and its direction of travel. Screwworm was eradicated from the United States decades ago through a sustained programme, and the eradication line has long been held well to the south through the release of sterile flies [s1]. A public-health determination tied to the "health and security of U.S. citizens living abroad" signals official concern about the pest's movement in the Americas and the risk of its return to US livestock herds, rather than an outbreak already inside the country [s1][s2].

It is worth being precise about what these authorisations do and do not cover. Every one of the four products is an animal drug, authorised for use in animals [s1]. The public-health emergency power is being used here to protect the animal supply chain and to respond to a cross-border threat, not to treat people. Screwworm can infest humans, but none of these authorisations addresses human treatment [s1].

Emergency use authorisation is also not the same as approval. An authorised product has not been through the full review that approval requires; it is cleared for use under defined conditions for as long as the emergency declaration stands, and each authorisation "contain[s], among other things, conditions on the emergency use" of the product [s1]. The FDA has used the same section 564 authority for human products in other emergencies, and the logic is the same: a faster route justified by the absence of an approved alternative.

What to watch

Whether the screwworm eradication line holds or the pest continues to move north; whether the FDA adds further authorisations or converts any of these products toward full approval; and whether the underlying emergency declaration is extended or allowed to lapse, since the authorisations depend on it.