FDA Issues Emergency Use Authorization for Drug to Prevent New World Screwworm in Multiple Species

FDA Grants EUA for CLiK Extra to Combat Screwworm

The U.S. Food and Drug Administration (FDA) issued an Emergency Use Authorization (EUA) for CLiK Extra (dicyclanil topical suspension) wound spray on August 7, 2026. This authorization is for the prevention of New World screwworm (NWS) infestations (myiasis) in a wide range of animal species, including sheep, cattle, goats, swine, camelids, and various captive and captured wildlife. Sponsored by Elanco US Inc., CLiK Extra is applied topically to wounds and functions as an insect growth regulator, disrupting larval development. While providing a new tool against NWS, the product is not FDA-approved or conditionally approved for any indication.

• The EUA specifically authorizes CLiK Extra for prevention of NWS myiasis associated with wounds, birth, and after surgical or husbandry procedures (e.g., dehorning, ear tagging, castration, tail docking, shearing). It is applicable to a broad range of species including sheep, cattle, goats, swine, camelids, cervids, American bison, bighorn sheep, and Sonoran pronghorn.
• CLiK Extra (dicyclanil) acts as an insect growth regulator, disrupting the development of New World screwworm larvae and halting their lifecycle before they can cause tissue damage in the host animal. This mechanism prevents infestation rather than directly killing existing larvae, and the product is available over the counter for topical use.
• This Emergency Use Authorization is based on scientific evidence suggesting CLiK Extra may be effective in preventing NWS myiasis, with its known and potential benefits outweighing risks. The EUA remains effective until revoked or the HHS Secretary terminates the public health emergency declaration, and it is important to note that CLiK Extra is not FDA approved or conditionally approved for any indication.

Addressing Unmet Needs in New World Screwworm Prevention

Current treatment approaches for New World screwworm (Cochliomyia hominivorax) myiasis face significant clinical and operational limitations that compromise both individual patient outcomes and broader eradication efforts. While mechanical debridement and insecticidal application remain the cornerstones of management, several persistent gaps undermine their effectiveness across diverse settings.

• Reliance on manual larval removal: Treatment depends heavily on physical extraction of larvae combined with wound debridement, a labor-intensive process that requires trained personnel and appropriate facilities — resources that are frequently unavailable in rural or resource-limited endemic regions where infestations are most prevalent.

• Limited pharmacological options and resistance concerns: The topical insecticides and systemic antiparasitic agents currently used (including organophosphates and ivermectin) have not been uniformly validated across all myiasis presentations, and repeated insecticide use raises ongoing concerns about the development of resistance in C. hominivorax populations, which could critically undermine both treatment and Sterile Insect Technique (SIT)-based eradication programs.

• Delayed diagnosis leading to advanced tissue destruction: New World screwworm larvae are obligate parasites that actively invade living tissue, and delayed recognition of infestation allows for rapid wound enlargement and secondary bacterial infection, significantly complicating clinical management and increasing morbidity.

• Challenges in vulnerable and non-human animal populations: Managing infestations in livestock, wildlife, and immunocompromised or pediatric human patients presents additional complexity, as treatment protocols are not well-standardized across species, and infected wildlife reservoirs can sustain transmission and re-infestation cycles that undermine regional control measures.

• Re-infestation risk in the absence of integrated vector control: Treating the wound without addressing environmental and entomological risk factors results in high re-infestation rates, highlighting the lack of effective patient- or herd-level preventive strategies beyond the large-scale SIT programs that are not always geographically accessible.

The Broad Impact of New World Screwworm Infestations

New World screwworm myiasis does not affect all individuals equally — specific demographic, clinical, and behavioral factors significantly elevate risk. Understanding these vulnerable populations is essential for timely clinical recognition and appropriate case management.

• Geographically at-risk individuals: Populations residing in tropical and subtropical regions of the Western Hemisphere — particularly parts of the Caribbean and South America where the parasite remains endemic — carry the highest baseline risk of exposure.

• International travelers: Returning travelers represent an increasingly recognized risk group, with documented cases including a 26-year-old presenting with otalgia and bloody otorrhea following travel to the Dominican Republic, and a 77-year-old male who developed cutaneous furuncular myiasis after visiting Brazil and Argentina.

• Immunocompromised patients: Individuals with significant immunosuppression face heightened susceptibility, as impaired host defenses reduce the ability to mount effective responses to larval infestation.

• Patients with open or malignant wounds: Existing wounds and extensive lesions create ideal oviposition sites for gravid female flies; this includes patients with malignant wounds such as those associated with maxillary sinus squamous cell carcinoma, as well as individuals with mucosal surface exposure.

• Socioeconomically vulnerable populations: Those with limited access to healthcare, poor hygiene conditions, or frequent proximity to livestock — the parasite's primary hosts — face compounding environmental and biological risk factors for infestation.

CLiK Extra EUA: A New Frontline Against Screwworm Reintroduction

The recent Emergency Use Authorization (EUA) for CLiK Extra, a dicyclanil topical suspension, marks a pivotal moment in the ongoing battle against the New World screwworm (NWS). This obligate parasitic fly poses a severe threat to animal welfare, agricultural productivity, and even human health, capable of causing devastating myiasis. While eradicated from the United States decades ago, the persistent endemicity of NWS in parts of South America and the Caribbean means the risk of reintroduction remains a constant concern, underscored by recent travel-associated human cases. CLiK Extra's authorization provides a crucial new tool, an insect growth regulator, for preventing infestations across a wide array of animal species.

This strategic move allows for the rapid deployment of a known active ingredient, dicyclanil, to address an urgent biosecurity need. Dicyclanil is already a prominent preventative chemical in other myiasis control efforts, such as against blowfly strike in Australian sheep. However, this expanded application comes with important considerations. Research indicates that other blowfly species have developed significant resistance to dicyclanil, often mediated by cytochrome P450 enzymes. This raises a critical risk that NWS could similarly develop resistance, potentially undermining the product's long-term efficacy and necessitating robust resistance management strategies from the outset.

Furthermore, while topical application is convenient, the effectiveness of such formulations can be influenced by factors like wool binding and limited systemic absorption, as seen with other insect growth regulators. This highlights the importance of optimal application techniques and understanding the product's performance across diverse animal anatomies and wound types. From a safety perspective, dicyclanil's established acceptable daily intake (ADI), derived from studies noting effects like increased plasma cholesterol in dogs and certain tumor incidences in mice at higher doses, underscores the need for careful adherence to application guidelines to mitigate potential public health and environmental exposures. Ultimately, this EUA reinforces the necessity of a comprehensive One Health approach, integrating surveillance, international collaboration, and adaptive control strategies to safeguard against this persistent and economically impactful parasitic threat.