FDA Issues Emergency Use Authorization for Drugs to Prevent and Treat New World Screwworm in Dogs and Cats

FDA Authorizes Capstar and Nitenpyram for Screwworm Prevention

The U.S. Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) for Capstar (nitenpyram) tablets and revised the EUA for its generic version, Nitenpyram Tablets. This authorization now covers both the prevention and treatment of New World screwworm (NWS) infestations (myiasis) in dogs, puppies, cats, and kittens weighing at least two pounds and four weeks old. This action addresses a previously unmet need for NWS prevention, as the generic version was initially authorized only for treatment in June 2026. The FDA concluded that the known and potential benefits of these over-the-counter products outweigh their known and potential risks for the authorized uses.

• The Emergency Use Authorization (EUA) expands the utility of Capstar and Nitenpyram Tablets to include both prevention and treatment of New World screwworm (NWS) myiasis. These products are specifically authorized for dogs, puppies, cats, and kittens that meet minimum criteria of weighing at least two pounds and being at least four weeks old, providing broader protection against NWS infestations in susceptible pet populations.
• This authorization marks a significant development as it provides the first FDA-authorized products for the prevention of NWS in dogs and cats, addressing a critical unmet need. Previously, Nitenpyram Tablets were only authorized for treatment. This offers veterinarians and pet owners new tools to protect animals, especially those in or traveling to identified NWS risk areas, despite the current low risk in most of the U.S.
• Capstar and Nitenpyram Tablets are available over-the-counter in two tablet sizes: 11.4 mg and 57 mg, with dosage determined by the pet's weight. The FDA's decision is based on the totality of scientific evidence, concluding that the products are reasonably believed to be effective and their benefits outweigh the risks. The EUAs will remain in effect until revoked or the HHS Secretary terminates the public health emergency declaration for NWS. Capstar is sponsored by Sergeant’s Pet Care Products LLC, and Nitenpyram Tablets by Felix Pharmaceuticals Pvt. Ltd.

Identifying Pets at Risk for New World Screwworm Infestations

New World screwworm (Cochliomyia hominivorax) myiasis affects a broad range of human patients, with several demographic and clinical factors consistently associated with increased susceptibility. Epidemiological data drawn from multiple geographic settings — including Brazil, Argentina, Colombia, and Mexico — identify overlapping risk profiles across case series.

• Age extremes: Both neonates and older adults are disproportionately affected. A 7-day-old infant presenting with umbilical cord myiasis illustrates vulnerability at the earliest stage of life, while the mean patient age in Mexico's 2025–2026 surveillance data was 61.1 years, with 76.7% of those patients carrying more than one concurrent condition.

• Male sex: Male patients are consistently overrepresented. In the Mexico surveillance cohort, 71.8% of cases occurred in men. A São Gonçalo, Brazil case series similarly recorded 12 male and 10 female patients, and studies in companion animals also noted intact males as the most commonly affected group.

• Underlying wounds and skin conditions: Open wounds are the primary portal of infestation. Seborrheic dermatitis and psoriasis have been identified as predisposing dermatoses, as illustrated by a case of scalp myiasis in a patient with a history of seborrheic dermatitis following travel to Brazil.

• Poor personal hygiene and low socioeconomic status: Poor personal hygiene, low educational level, and very low income are documented as secondary susceptibility factors in case series from Rio de Janeiro, Brazil.

• Alcohol use, physical or mental disability, and bedridden status: Alcoholism, bedridden status, and physical or mental disability are reported as additional risk factors across multiple case series, alongside cancer and drug use.

• Geographic concentration: In the Mexico 2025–2026 outbreak, cases were concentrated in southern Mexico, particularly Chiapas, followed by Yucatán, Oaxaca, and Quintana Roo, consistent with the broader pattern of endemicity in tropical and subtropical regions with poor sanitation and cattle presence.

Nitenpyram's Place in the NWS Treatment Guidelines

The current standard of care for New World screwworm (NWS) myiasis is multimodal, combining mechanical larval removal with pharmacologic, antimicrobial, and supportive interventions. Mechanical removal of maggots remains the foundational step across anatomical sites and patient populations. This is consistently supplemented with systemic antibiotics to address secondary bacterial infection, wound debridement and lavage, and tetanus prophylaxis. In cases involving underlying conditions — such as diabetes, malignancy, or uterovaginal prolapse — management of the predisposing disorder is integral to treatment. Ivermectin, a macrocyclic lactone that targets glutamate-gated chloride channels, has been employed as a pharmacologic antiparasitic adjunct, as documented in a case of anorectal myiasis caused by Cochliomyia hominivorax.

Spinosad has been evaluated as a treatment option in canine NWS myiasis caused by Cochliomyia hominivorax, with a single oral dose of spinosad 560 mg demonstrating an overall efficacy of 79.7% (56.7–100%). The average larval expulsion rate was 73.3% (56.7–100%), reaching its maximum within 6 hours post-treatment, while the average larvicidal effect was 23.7% (0–58.3%). No animal required a second dosage at 24 hours post-treatment, and lesions were completely healed within 8 days post-treatment. The authors noted that, despite not reaching the desirable 100% efficacy, spinosad treatment is an option in managing NWS myiasis in conjunction with mechanical removal of maggots that remain in the lesion and support treatment. In Venezuela, control of myiasis in animals has been achieved through organophosphorus compounds, macrocyclic lactones, and a foamy spray based on spinosad, with concerns raised about insecticide resistance to organophosphorus compounds.

In human cases, additional management strategies documented in the literature include bedside debridement, pharmacologic antiparasitics, biopsy of surrounding tissue, and reporting to the appropriate health agency. In one series of head and neck myiasis cases superimposed on cutaneous malignancy, external beam radiation therapy for the underlying malignancy had the added benefit of eradicating the larvae. Proper wound care — including wound lavage, antisepsis with agents such as aqueous chlorhexidine 0.12%, and application of repellents around wounds — has also been described as part of comprehensive management. The knowledge base does not have sufficient information on this aspect regarding any formally codified, universally adopted clinical guideline document specifically governing NWS treatment in humans.

Bolstering Defenses Against Re-Emerging Screwworm Threat

The recent Emergency Use Authorization (EUA) for nitenpyram, both branded and generic, to prevent and treat New World screwworm (NWS) infestations in companion animals marks a pivotal moment in veterinary public health. This move by the FDA is a direct response to the persistent and re-emerging threat of NWS, a parasite capable of causing devastating myiasis in animals and posing a risk to human health. The authorization for prevention is particularly impactful, shifting the paradigm from reactive treatment to proactive defense.

Nitenpyram's established rapid larvicidal efficacy against NWS, with studies showing 100% efficacy in naturally infested dogs, makes it a powerful tool. Its over-the-counter availability ensures broad accessibility, enabling pet owners and veterinarians to act swiftly, which is crucial given the rapid spread rates of NWS outbreaks linked to animal movement. This strategic deployment aligns with the urgent need for enhanced control measures, active surveillance, and regional cooperation highlighted by the parasite's northward spread from Central America and its potential reintroduction into previously eradicated areas.

However, the expanded use of nitenpyram, a neonicotinoid insecticide, also brings important considerations. Research indicates that neonicotinoids can pose significant ecological risks to aquatic environments, a factor that warrants careful monitoring and responsible use practices. Furthermore, while effective, nitenpyram's traditional application for severe myiasis cases has often involved aggressive debridement and anesthesia, suggesting that for advanced infestations, veterinary intervention beyond drug administration may still be necessary. The landscape of myiasis treatment is also evolving, with newer options like spinosad/milbemycin and lotilaner demonstrating rapid efficacy against other screwworm species, sometimes negating the need for extensive procedures. This suggests a dynamic competitive environment and an ongoing need for integrated, multi-faceted approaches to parasite control, firmly rooted in a One Health framework that considers animal, human, and environmental well-being.