Friends of the Riney Canine Health Center,
If you’ve seen New World Screwworm mentioned in the news lately and wondered whether it is something you actually need to worry about with your own dog, that’s exactly what I want to talk about this month. For most pet dogs in the United States, the current risk remains low. However, it is worth knowing what screwworm is, what signs to watch for, and when to call your veterinarian.
New World Screwworm is the larval stage of a specific type of fly: Cochliomyia hominivorax. Fly larvae are also called maggots, which many of you have probably seen before. The difference is that typical maggots usually feed on dead or decaying tissue, while New World Screwworm larvae feed on living tissue, allowing them to damage healthy tissue and make wounds progressively worse.
The female screwworm fly can lay her eggs in open wounds, scrapes, surgical incisions, or even moist areas around the eyes, nose, or genitals. Once the eggs hatch, the larvae burrow into tissue as they feed and grow. The name “screwworm” comes from this screw-like feeding motion. As the larvae damage tissue, the wound can become larger and may attract additional flies. I’ll spare you the photos because they are exactly as unpleasant as you might imagine.
The reason this has become a concern again recently is that the USDA eradicated New World Screwworm from the United States in the 1960s. This involved breeding and releasing millions of sterile male flies. Because female screwworm flies typically mate only once, mating with a sterile male prevents the production of viable offspring and eventually collapses the population.
For decades, the containment line remained in Panama. Starting around 2022, screwworm has been moving northward through Central America and Mexico, and the USDA has now confirmed detections in the United States, including livestock in Texas and a dog in New Mexico.
So, should you be worried about your own dog? At this time, the concern for most dogs is low, but awareness is important. The highest-risk situations involve dogs that have been in the affected areas and have an open wound, surgical incision, or another moist area where flies can lay eggs. A good habit is checking any wound or incision daily until it is fully healed. Contact your veterinarian if you notice a wound that is getting worse instead of better, an unpleasant odor, or especially if you see any visible larvae or maggots in or around a wound.
If you travel internationally with your dog, especially to areas where screwworm is present, be sure to review current USDA and CDC requirements before returning to the United States. If you recently traveled or imported a dog and they develop a wound, especially after travel in an affected region, contact your veterinarian right away.
New World Screwworm is a federally reportable disease, meaning veterinarians work with state and federal animal health officials if it is suspected. While that may sound alarming, it is actually part of what helps identify cases quickly and coordinate an appropriate response. Several medications, including NexGard (afoxolaner), Credelio (lotilaner), and nitenpyram, have received FDA Emergency Use Authorizations for treatment of New World Screwworm infestations in dogs. Successful treatment also requires prompt veterinary care for physical removal of larvae and wound management.
Again, while the current risk for most dogs remains low, we'll continue to monitor this situation closely and keep you informed if recommendations change. As always, thank you for being a member of the Riney Canine Health Center. We look forward to catching up with you next month.
Dr. Aly Cohen
Extension Veterinarian
Cornell Richard P. Riney Canine Health Center
Visit our website today for more canine health topics and give your furry friend the care they deserve.
Questions: Discover expert tips, personalized advice and friendly support from our Big Red Bark Chat AI Assistant!