Should Dog Owners Be Worried About the Spread of This Flesh-Eating Parasite? 

Key points: 

• The veterinary community is monitoring the recent northward spread of the New World screwworm, a blowfly that lays eggs in warm-blooded animals. 
• The insects can be devastating to their hosts, including dogs. 
• Though the fly has not yet reached the United States, the United States Department of Agriculture (USDA) is preparing to combat its spread by opening a multi-million dollar facility in Texas that breeds sterile male screwworms to mate with egg-laying females. 
• In the meantime, it’s advised that dog owners refrain from taking their pets to areas with active outbreaks. 

The American Veterinary Medical Association is warning the veterinary community about the spread of a parasitic fly that targets warm-blooded animals—including dogs. It’s called the New World screwworm (NWS). A natural barrier in Panama previously contained screwworms, but they’ve moved northward into other Central American countries over the past couple of years—likely traveling with livestock. As of now, the screwworms haven’t reached the United States, but their proximity has alarmed agriculture professionals. According to the U.S. Department of Agriculture (USDA), the northernmost sightings of these insects have been in Oaxaca and Veracruz, which are around 700 miles south of the U.S. border, in May.

Here’s what you should know to protect your four-legged loved ones—and yourself—from these dangerous parasites.

What danger do New World screwworms pose to dogs?

Screwworms’ method of infestation sounds as ghastly as their name: female flies lay eggs in open wounds, and the eggs produce flesh-eating larvae. Their scientific name, Cochliomyia hominivorax, translates to “man-eating blowfly” (homini– meaning “man,” and –vorax meaning “devouring.” Cochliomyia is the genus for “blowfly”). Because it burrows into warm-blooded animals, the screwworm is a danger to pets as well as livestock, wildlife, and—to a lesser extent—humans. Discovery and treatment are essential; without them, the infestation can be fatal. 

How do I identify an infestation?

New World screwworms burrow in abraded flesh, so any lesion would appeal for egg-laying. According to the Centers for Disease Control and Prevention (CDC), a wound “as small as a tick bite” could attract a female screwworm. Once the eggs hatch into the larval stage, the site gets a foul smell (like decay) and has visible maggots in it. The wounds are painful and grow instead of healing, so your dog may bite or lick the affected area. Your pup could also exhibit an unusual restlessness or lethargy, according to Texas A&M’s AgriLife Extension. 

Sounds bad! How nervous should I be? 

Be aware, but don’t panic. Again, as far as we know, the New World screwworm hasn’t yet reached the United States. Sonja Swiger, Ph.D., a veterinary entomologist at Texas A&M AgriLife, says: “At this time, everyone should educate themselves on what NWS is. Know the signs and the impact. But the fly cannot get here by itself—meaning it will only come into the U.S. by human or animal transport.”

Agricultural agencies in various countries have consistently monitored the parasites, Dr. Swiger adds, and international travel has been restricted for certain animals. The best way to prevent spread is avoiding travel to areas with active outbreaks—and definitely refrain from taking your dog there. 

“As a dog and cattle owner myself in Texas, I’m not any more concerned about NWS than I was last year, but I will be sure to address any wounds I find on my animals,” Dr. Swiger says. 

So what do I do if I spot an affected wound on my dog?

If you suspect that your dog is infected with NWS, call your veterinarian for treatment immediately. The USDA has also provided guidance to animal-health professionals for reporting a sighting.  

How are we fighting them? 

The good news is that the U.S. has successfully dealt with these insects before. It’s been around 60 years, but the flies were eradicated here in the middle of the last century—though there have been isolated outbreaks in the years since (the last of which was in 2017, when an outbreak in the Florida Keys and the Everglades decimated a local deer population and infected one dog). The method for combating their spread back in the 1960s is the same one used now: Breeding sterile male flies to mate with egg-laying females. 

The spread can be devastating to livestock, so the government is taking the threat especially seriously. The USDA announced last week that it plans to open an $8.5 million facility in Texas to breed and release these sterile males. The facility is slated to open by the end of the year. The government will spend another $21 million on converting a facility in Mexico once dedicated to fruit flies into a screwworm breeding factory. One such facility already exists in Panama. The plan is to re-establish the barrier against these dangerous insects. 

In the meantime, take Dr. Swiger’s advice: Keep your dog out of affected areas, monitor their wounds, and immediately contact your vet if something looks (or smells) off.