By Andi Anderson
The New World Screwworm (NWS), a parasitic fly once eradicated in the United States, is raising fresh concern as outbreaks spread across Central America and Mexico.
On August 18, 2025, the Secretary of Health and Human Services issued an emergency declaration, warning that the parasite poses “a significant potential to affect national security or the health and security of United States citizens living abroad.”
The emergency status allows veterinarians to use certain animal drugs under extra-label provisions to help control potential infestations. These measures are critical as the pest has the potential to re-enter the U.S. and threaten livestock, pets, wildlife, and even humans.
NWS is caused by the fly Cochliomyia hominivorax, which lays its eggs in open wounds or natural body openings. Once hatched, larvae burrow into living tissue, causing painful and often life-threatening infections called myiasis. Infestations tend to peak in warm spring and summer months when the fly thrives, while cold winters suppress its spread.
Farmers and livestock owners are urged to monitor animals closely. Warning signs include restlessness, isolation from the herd, head shaking or rubbing, foul odors of tissue decay, and visible maggots in wounds. Even minor injuries such as castration, dehorning, or the navel of newborn animals can be targeted.
Currently, no FDA-approved animal drugs exist for treating NWS. However, with the emergency authorization, veterinarians can access specific treatments under prescription, including topical parasiticides, wound dressings, insecticides, and systemic options where appropriate.
Farmers are advised to maintain close communication with their herd veterinarians to ensure timely diagnosis and treatment.
Prevention remains the most effective defense. Producers should promptly treat wounds with approved insecticides or dressings, monitor pets returning from abroad, and follow strict inspection requirements for animals coming from screwworm-affected countries.
With the pest pressing closer to U.S. borders, vigilance is key. As experts emphasize, “an ounce of prevention is worth a pound of cure” when it comes to protecting animal health from the threat of New World Screwworm.
Photo Credit: gettyimages-zoran-zeremski
Categories: Ohio, Rural Lifestyle, Farm Safety