July and August in Ontario are usually seen as the season for BBQs, trips to the beach, sunbathing, and in the veterinary world, cuterebra. This gruesome little critter may not be the most talked-about parasite of the summer, but (contrary to its “cute” name) it certainly has the most gross-out value.
So, what is cuterebra anyway? It’s a term for the larvae, or maggots, of a group of “warble flies” that infect small animals like rodents, rabbits, dogs, and of course, cats. As adults these flies are harmless bee-mimics; they don’t sting, don’t bite, and mainly mind their own business. They like to lay their eggs at the entrance to rodent burrows, and that’s where the fun starts.
Cuterebra eggs are inhaled, swallowed, or enter the eyes or ears of rodents returning to their burrows (or dogs and cats sniffing around). Once inside their host, the eggs hatch and the larvae burrows though muscle and tissue to form a burrow with a round “breathing hole” in the animals skin. This process can take anywhere from 3 to 5 weeks. In rodents, the larvae erupt around the animal’s back or groin, but in cats it is usually on the underside of the neck. The larvae then lives here for a period of weeks, growing and maturing. When they reach adult size, they wiggle out and fall on to the ground in a cocoon, which hatches to release an adult fly that repeats the cycle.
Appearance and Treatment
At the cat clinic, we often see cats with cuterebra arrive for a “wound on the neck”. The breathing hole of the maggot is usually surrounded by a firm ring of scar tissue and may have some blood on the fur around it. The larvae itself will usually hide deep in its burrow, but if you look long enough you will see it stick it’s head out to breathe.
Though painful and an infection risk, these cuterebra are not usually a major problem for the animal and are easily dealt with by a veterinarian. At the Cat Clinic, we use a combination of local anesthesia, flushing the wound, and delicate forceps to pluck them from their burrow. It’s important to not try this at home- accidently rupturing the worm is easy and can lead to infection or even life threatening anaphylactic shock.
Cuterebra become really dangerous when they migrate to the wrong spot and end up in the nose (blocking off the flow of air), the inner ear (causing balance and hearing issues), or even the brain (causing a severe and life threatening disease called “Feline Ischemic Encephalopathy). These conditions require immediate veterinary attention.
There are no repellants or drugs available to prevent cuterebra infestation, so the most important part of prevention is keeping cats indoors and away from rodent burrows. Cuterebra is most commonly seen in kittens, who may pick eggs up from the environment or off of their mother’s fur, so a hygienic indoor environment is very important for these little ones. Remember though that cats of all ages can be infected. Animals that have one larvae often have others (the Cat clinic has removed 10 larvae from 4 kittens so far this year) so keeping a close eye on any animal with a history of cuterebra is important.
Written by Dr. Matthew Kornya DVM