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NWS has arrived. What’s the true clinical picture for equine veterinarians?

By Sally DeNotta, DVM, PhD, DACVIM

One year ago, New World screwworm (NWS) was a looming threat for equine veterinarians. Today, it’s a clinical reality.

The conversation has shifted from preparedness to rapid detection, response and reporting. The priority now is recognizing suspect cases quickly, initiating treatment and reporting cases before additional spread can occur.

RECOGNIZING CLINICAL SIGNS
Compounding that urgency is a significant diagnostic challenge: Most U.S. equine veterinarians have never encountered NWS. Maintaining a high index of suspicion is essential.

Carefully examine any traumatic, surgical, umbilical or mucocutaneous wounds that heal slowly, fail to heal, or appear more painful than expected.
Avoid discarding larvae as they can pupate into adult flies and spread to new hosts. Instead, collect specimens for identification and immediately report suspected cases.

Early recognition remains one of the profession’s most effective tools for limiting disease spread. Prompt treatment and notification of animal health officials will be critical. Until sterile fly production reaches the scale needed for eradication, rapid detection and treatment remain the profession’s most critical line of defense.

TREATMENT GUIDANCE
Treatment recommendations also continue to evolve.

As treatment options expand through Emergency Use Authorizations, extra-label protocols and new approvals, practitioners should rely on current federal guidance. Veterinarians and horse owners are encouraged to regularly consult screwworm.gov for the latest USDA and FDA recommendations on approved treatments and regulatory requirements.

When products are used under Emergency Use Authorization or extra-label provisions, veterinarians should discuss the product’s regulatory status with clients while maintaining appropriate treatment records and adverse event reporting, when required.

Beyond clinical care, equine veterinarians serve on the front lines of the national surveillance system. Recognizing suspect cases, collecting diagnostic samples, reporting cases and advising clients on movement requirements remain essential responsibilities throughout the eradication effort.
Horse owners should continue to rely on their veterinarians for practical guidance as movement restrictions and reporting requirements evolve.

MANAGING WHAT’S AHEAD
The outlook for the next year will largely depend on the speed of case detection, reporting, movement compliance, and implementation of sterile insect release and coordinated control measures.

Strong compliance with movement restrictions and successful implementation of sterile insect release programs could limit further geographic expansion. Delayed detection, missed infestations or movement of animals from affected areas, however, could complicate eradication efforts.

While freezing temperatures make it unlikely that NWS will become endemic across the northern United States, the Southeast—where temperatures remain temperate year-round—is more vulnerable to long-term establishment.

ERADICATION WILL TAKE TIME
Sterile fly production is central to long-term eradication, but new facilities won’t be ready to produce and distribute at the scale needed for months, and likely years. Until they are, equine veterinarians can make an immediate difference by helping clients integrate NWS prevention into routine horse care through regular wound inspections, prompt wound management, effective fly control, and client education.

Continued collaboration among veterinarians, producers, diagnostic laboratories, and state and federal animal health officials will be essential to protect the U.S. equine industry and achieve long-term eradication. Until eradication is achieved, vigilance remains the profession’s most effective defense.

FOR MORE INFORMATION
USDA APHIS NWS Information
Equine Disease Communication Center

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