New World Screwworm Threat Prompts U.S. Border Closures and Actions

In light of recent developments, the New World screwworm (NWS), a parasitic threat to livestock, is prompting urgent measures from U.S. federal agencies to prevent its entry. With southern ports closed to livestock trade from Mexico and coordination efforts intensifying, stakeholders are advised to adopt strategic precautions.

Understanding the Threat and Response

The New World screwworm (Cochliomyia hominivorax) is a parasitic fly that poses significant risks to warm-blooded animals by infesting their flesh. Though eradicated from the U.S., recent detections in nearby Mexico have triggered a comprehensive response involving multiple federal agencies. Southern ports remain closed to livestock trade from Mexico as a precautionary measure.

In August 2025, the USDA unveiled a multifaceted strategy to address this threat, including constructing a sterile fly dispersal facility in McAllen, Texas, collaborating with Mexico, and discussing emerging technologies like genetically engineered flies.

Regulatory Developments and Authorizations

On August 18, 2025, the Department of Health and Human Services declared a public health emergency, allowing the FDA to expedite the use of certain animal drugs for NWS myiasis. Emergency Use Authorizations (EUAs) have been granted for various treatments, including lotilaner for cats, afoxalaner for dogs and cats, and cypermethrin sprays for several species.

The FDA continues to work with drug sponsors to explore new treatment options, although no medicated feeds have been approved for NWS myiasis. Sponsors seeking authorization can reach out to AnimalDrugNWS@fda.hhs.gov.

Implications for Various Stakeholders

Livestock Producers

With an NWS outbreak potentially costing over $2 billion, livestock producers are urged to implement rigorous inspection protocols, align reporting with APHIS requirements, and review their sourcing and supply chain strategies. Evaluating insurance coverage for NWS-related losses is also recommended.

Animal Drug Sponsors

Sponsors should assess the expedited authorization process, communicate with the FDA about potential pathways, and align their development programs with identified data needs. Exploring compounds that can be repurposed for NWS treatment is also advised.

Veterinary Practitioners

Veterinarians should familiarize themselves with authorized NWS prevention products, incorporate APHIS reporting protocols, and educate clients about early detection and wound monitoring.

Trade and Supply Chain

Companies reliant on livestock movement across borders should stay informed about USDA restrictions, consider alternative sourcing, and scrutinize force majeure clauses in existing contracts to ensure coverage for government-imposed disruptions.

Additional Resources and Steps

Stakeholders can access up-to-date information on screwworm.gov and the FDA’s animal drug page. It's advised that companies appoint NWS point persons for efficient handling of developments and review current biosecurity measures to align with federal actions.

If you have questions about these developments, please contact Driscoll R. Ugarte, Brandon A. Chan, Ph.D., Victoria (Tori) Hawekotte, Taylor Hertzler, or other Life Sciences and Medical Technologies Industry Group attorneys.