Companion Animal Care in the Face of the New World Screwworm (NWS) Threat

Introduction: Understanding the NWS Threat to Companion Animals 

 The New World Screwworm (NWS), Cochliomyia hominivorax, is a myiasis-causing parasitic fly native to the Americas. Since the 1970s, the NWS has been successfully eradicated from the United States, with successful eradication in Mexico and most of Central America in the 1990s and 2000s. This was done through the mass release of sterile male flies (sterile insect technique). 

A recent New World Screwworm outbreak and range expansion from Panama north through Central America and into southern Mexico brings concern for a possible introduction into the United States. 

While livestock and wildlife represent most NWS cases in a given area, dogs and cats are also at risk. The ensuing myiasis from a larval infestation may be fatal for dogs and cats, depending on anatomic location and severity of the infestation, care, and timing of the diagnosis. 

Monitoring and Surveillance 

• Check pets daily for the presence of potential wounds, including sites of previous tick bites/attachment. 
• Monitor for a foul odor, tissue damage, or signs of fly larvae in wounds (myiasis). 
• Body secretions and wound discharges may attract NWS females for oviposition. 
• Assess the pet’s environment for possible fomites that may cause injury (e.g., metal collars or chains, wire fencing, sharp vegetation, etc.). 
• Avoid risky behavior for dogs and cats, especially those with outdoor access (e.g., animal aggression/fighting and accidents). 
• Provide adequate care and dressing of any wounds, including recent surgical incisions (e.g., spay/neuter, caudectomy/tail docking, amputation, etc.). 
• Observe pets for unusual behavior, such as wound-licking or irritation. Animals may lose interest in food, and may become aggressive or lethargic due to irritability and associated infestations. 
• Visit your local veterinarian immediately if myiasis is suspected.

Treatment

Consult with your local veterinarian immediately if myiasis from New World Screwworm is suspected. 

A veterinary professional should inspect and must promptly remove (and kill) all fly larvae. They must also clean suspect lesions and wounds. Sedation may be necessary. 

Mechanical removal of maggots should occur immediately, and removed larvae should be stored in 70 percent ethanol and submitted for diagnostics. Veterinarians may submit up to 10 maggots to the National Veterinary Services Laboratories for identification (Specimen Submission: tx.ag/ specimensubmission). All maggots that are not submitted must be killed, either by freezing or in alcohol. 

Nitenpyram-based oral products are an effective treatment but have no preventive efficacy.* 

Isoxazoline-based oral products (tablets and chewable tablets) have a proven treatment efficacy and are likely to have preventive efficacy*. In October 2025, the U.S. Food and Drug Administration (FDA) issued an emergency use authorization (tx.ag/animaldrugNWS) for lotilaner to be administered to dogs for treatment of NWS, and later for cats (November 2025). 

Conclusion

New World Screwworm has NOT been found in the U.S. at this time. However, pets near the U.S. southern border and those traveling to and/or from Latin America should be monitored regularly. 

Contact your veterinarian to discuss whether pretreatment for dogs and cats traveling to and from Latin America is warranted. 

Early detection of NWS myiasis is essential for effective treatment and clinical recovery of pets. 

Daily inspection for wounds and proper care of existing wounds/lesions are necessary to avoid NWS infestation and reinfestation. 

Using flea, tick, and mite medications as needed for parasite management will help prevent pet(s) from a NWS attack, if they become exposed. 

Other mammalian pets such as ferrets, rabbits, and guinea pigs are also at risk of NWS infestation.