The New World screwworm is not currently present in the United States in livestock or other animals, though all southern ports of entry are closed to livestock trade from Mexico due to the threat.

The New World screwworm (NWS), Cochliomyia hominivorax, is a parasitic fly whose larvae burrow into the flesh of warm-blooded animals, feeding on healthy tissue and causing myiasis that is often fatal if left untreated. NWS can infest livestock, pets, wildlife and, in rare cases, people. Although long eradicated from the United States, NWS has moved northward through Central America and Mexico in recent years, prompting a sweeping multiagency federal response. This Alert outlines the key regulatory developments and identifies practical steps that livestock producers, animal drug sponsors, veterinarians and supply chain participants should consider now to manage compliance obligations and mitigate risk.

Current Status and Federal Response

NWS is not currently present in the United States in livestock or other animals, though all southern ports of entry are closed to livestock trade from Mexico due to the threat. Confirmed NWS detections in the Mexican state of Tamaulipas, approximately 200 miles from the U.S. border, have heightened urgency. In August 2025, a single traveler-associated human case was confirmed in Maryland; United States Department of Agriculture (USDA) surveillance in the surrounding area found no NWS presence, and the public health risk was assessed as very low.

In August 2025, USDA Secretary Brooke Rollins announced a comprehensive five-part strategy covering border protection, containment in Mexico, domestic readiness, infrastructure investment and innovation. Key initiatives include construction of a sterile fly dispersal facility at Moore Air Base in McAllen, Texas, a planned domestic sterile fly production facility developed with the U.S. Army Corps of Engineers, daily coordination with Mexico’s SENASICA agriculture agency and public listening sessions on emerging technologies such as e-beam sterilization and genetically engineered flies.

HHS Emergency Declaration and FDA Emergency Use Authorizations

On August 18, 2025, The Department of Health and Human Services issued a declaration of emergency under the Federal Food, Drug and Cosmetic Act, determining that NWS presents a significant potential for a public health emergency that could affect national security. This declaration allows the  Food and Drug Administration (FDA) to authorize the emergency use of certain animal drugs for NWS myiasis. Since then, FDA has issued emergency use authorizations (EUA) permitting access to unapproved medical products or unapproved uses of approved medical products for the diagnosis, treatment and prevention of NWS myiasis. Such treatments for NWS myiasis under EUA include lotilaner for cats (November 2025), afoxalaner for dogs and cats (February 2026), cypermethrin spray and topical ointment for multiple species including cattle, sheep, goats, horses and birds (March and April 2026), a coumaphos, propoxur and sulfanilamide topical powder for cattle, swine, goats, sheep, horses, donkeys, domestic hybrid equids and exotic zoo mammals (April 2026) and a doramectin injectable for cattle, horses, swine, sheep and deer (May 2026).

FDA’s Center for Veterinary Medicine continues to work with drug sponsors and federal and state partners to expand treatment options. No medicated feeds have been approved for NWS myiasis for any species, and data on oral administration of ivermectin or doramectin for NWS in cattle or wildlife remains limited. Animal drug sponsors interested in pursuing an approval or authorization should email AnimalDrugNWS@fda.hhs.gov.

What This Means for Your Business

Livestock Producers

With the potential economic impact of an NWS incursion estimated at more than $2 billion and southern ports already closed to Mexican cattle imports, producers face both immediate supply constraints and longer-term biosecurity risk. Producers should take the following steps now:

1. Implement daily wound inspection and monitoring protocols for all livestock;
2. Confirm that internal reporting procedures align with Animal and Plant Health Inspection Service (APHIS) requirements for suspected NWS cases; failure to report can result in civil penalties and potential liability;
3. Review sourcing and procurement plans in light of ongoing port closures;
4. Audit force majeure clauses in livestock procurement and supply agreements to determine whether the current government-imposed trade restrictions qualify as triggering events, and assess whether existing clauses are broad enough to encompass future biosecurity-related government action; and
5. Review livestock risk protection, mortality and business interruption policies to confirm whether losses attributable to NWS infestation, quarantine or trade restrictions are covered or excluded.

Agricultural employers in border states should also be aware of potential OSHA general duty clause considerations for field workers given the confirmed, though rare, risk of human NWS infestation.

Animal Drug Sponsors

The HHS emergency declaration has created an expedited authorization pathway that sponsors should actively evaluate. Concrete next steps include:

1. Contacting FDA at AnimalDrugNWS@fda.hhs.gov to discuss EUA, conditional approval or standard approval pathways;
2. Reviewing FDA’s identified priority data gaps to align development programs with agency needs; and
3. Assessing existing product portfolios for compounds that may be repurposed for NWS indications.

Veterinary Practitioners

Veterinarians should take three immediate steps:

1. Familiarize themselves with FDA’s NWS information page to identify currently authorized prevention and treatment products;
2. Review and incorporate APHIS reporting protocols into clinic standard operating procedures so that any suspected NWS detection triggers timely notification to the appropriate state veterinarian or APHIS; and
3. Educate clients—particularly those with livestock or animals that travel internationally—about wound monitoring and early detection.

Trade and Supply Chain

Companies dependent on cross-border livestock movement should:

1. Monitor USDA’s animal health status determinations and port of entry restrictions on an ongoing basis;
2. Evaluate alternative sourcing arrangements in the event that closures extend beyond current timelines; and
3. Review force majeure and supply interruption provisions in existing procurement contracts to confirm coverage for government-imposed trade restrictions—paying close attention to notice procedures, mitigation requirements and whether clauses address delivery flexibility and price pass-through during extended disruption.

Key Resources and Next Steps

All affected stakeholders can bookmark and regularly monitor screwworm.gov and FDA’s animal drug page. Given the pace of regulatory activity, companies should designate internal points of contact for NWS-related developments and consider whether existing biosecurity, procurement and regulatory compliance programs require updating in light of these federal actions.

While there are currently no active reports of NWS infestation in the United States, in preparation for any possible outbreak, those in the veterinary pharmaceutical industry may be seeking approval or authorization for NWS treatment. Thus, interested industry players may consider the aid of regulatory counsel to ensure that veterinary drug candidates for treating NWS myiasis meet and comply with all of the requisite requirements to achieve EUA or full authorization. In anticipation that the risk of NWS outbreak will only increase, thereby increasing interest in an effective, comprehensive treatment, the veterinary pharmaceutical industry will likely be investing significant effort and resources in the research and development of such a treatment. Thus, industry players should also consider engaging intellectual property counsel to ascertain the current patent landscape, whether there is freedom-to-operate for a proposed NWS treatment, and to provide assistance in securing and enforcing patent rights as to the NWS treatment.

For More Information

If you have any questions about this Alert, please contact Driscoll R. Ugarte, Brandon A. Chan, Ph.D., Victoria (Tori) Hawekotte, Taylor Hertzler, any of the attorneys in our Life Sciences and Medical Technologies Industry Group or the attorney in the firm with whom you are regularly in contact.

Disclaimer: This Alert has been prepared and published for informational purposes only and is not offered, nor should be construed, as legal advice. For more information, please see the firm's full disclaimer.