The USDA has recently discovered cases of NWS in livestock and companion animals in New Mexico and Texas. While this situation is being monitored closely and we have not seen any signs of NWS in Arizona yet, we are encouraging our clients to be aware of the risks and prevention options for this deadly parasite.

Shielding Pets from Screwworm: A Prevention Guide

Preventing a screwworm infestation in your pets relies on a strict combination of vigilant wound management, limiting exposure in high-risk zones, and utilizing approved insecticide treatments.

Understanding the Risk

The New World Screwworm (Cochliomyia hominivorax) is a parasitic fly whose larvae target living tissue. Unlike typical blowflies that feed on dead flesh, the female screwworm fly deposits eggs near open wounds, fresh scratches, or natural body openings of any warm-blooded animal. The emerging maggots aggressively burrow into and feed on the host’s living flesh.

If left untreated, this can cause devastating tissue damage, severe illness, or death. Pets with existing injuries, deep skin folds, or those spending significant time outdoors are highly susceptible—particularly if they travel to or live in endemic regions across Central and South America. While the United States is currently free of endemic screwworm populations, constant vigilance is necessary for any animal traveling abroad or being imported from international locations.

Strategic Preventive Measures

• Meticulous Wound Inspection: Clean and monitor all punctures, scrapes, or post-surgical incisions on your pet immediately. Keep injuries protected and check them daily for any signs of fly activity, foul odor, or unusual drainage.

• Environmental Protection: When living in or visiting endemic zones, keep pets indoors or within screened enclosures, especially during peak fly hours. Use species-appropriate, veterinary-approved insect repellents when outdoor exposure is unavoidable.

• Travel Protocols: Before visiting regions known to harbor screwworms with your pet, obtain a formal veterinary health inspection certificate. Comprehensive veterinary examinations before and after international travel are highly recommended.

• Parasite Prevention: Maintain a consistent, year-round parasite prevention schedule tailored to your specific pet species. For many animals, modern systemic treatments and macrocyclic lactones provide highly effective protection against larval infestations. Credelio Quattro (for dogs) and Credelio feline (for cats) is currently the only parasite prevention that has FDA approval for the prevention and treatment of NWS.  Please contact us if you are interested in starting your pet on this medication for prevention of screwworm as well as multiple other harmful parasites. Always consult a veterinarian, as certain medications highly effective in one species can be toxic to another (e.g., specific dog medications are dangerous for cats).

Medical Intervention & Reporting

Veterinary care typically involves the mechanical removal of the larvae combined with localized and systemic larvicidal treatments. Medications like ivermectin or doramectin are frequently utilized by veterinarians to manage risk and treat infestations, particularly in quarantine or high-risk travel scenarios.

⚠️ Critical Reporting Mandate: Because screwworm poses a catastrophic threat to pets, wildlife, and livestock alike, any suspected infestation must be reported instantly to state animal health authorities and the USDA APHIS Area Veterinarian in Charge.

Stay Informed

Screwworm distribution and travel alerts can change rapidly. Pet owners, rescues, and veterinarians should consult official agricultural channels to stay updated on the latest security protocols, outbreaks, and travel regulations:

• For specific guidelines on identifying, treating, and halting infestations, visit the USDA APHIS Screwworm Resource Center.

• For broad animal health announcements and international pet travel requirements, monitor the main U.S. Department of Agriculture (USDA) portal.