What's Hiding in That Lump On Your Pet's Skin?

Published: November 21, 2013
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Veterinarians see a lot of gross things in practice – severe injuries, festering wounds, maggots, blowout diarrhea, but worst of all, in my opinion, are warbles. The official veterinary term for the condition is “cuterebriasis.”

Warbles are lumps in the skin caused by the presence of bot fly (Cuterebra) larvae. The flies normally lay their eggs near the burrows of wild rodents or rabbits, but the larvae that hatch from the eggs in July, August, and September can also attack nearby dogs and cats by burrowing through the skin, entering through body openings, or being eaten when the pet licks his or her fur.

Veterinarians treat patients with masses in or under their skin on a daily basis. Warbles are fairly nondescript lumps around a small hole in the skin. Usually, a little bit of discharge or crusty debris surrounds the hole. When I see something like this, I typically shave the fur from the area to get a better look at what’s going on and palpate (feel) the mass so I can plan the best course of action.

Trauma and infection are likely causes of draining masses. Perhaps a dog ran into a small stick on a hike and now has a bit of wood stuck under his skin, or maybe a cat has a draining abscess that resulted from a fight. These scenarios are far more common than cuterebriasis. Whatever the most likely cause, treatment usually involves sedating the pet, opening up the lump, and cleaning out what’s inside. This is the point at which I have, on several occasions, come awfully close to shrieking like a six-year-old girl. What’s inside a warble is not the expected pus or debris, but a freakishly large (one centimeter or so), wriggling larva that looks like it should star in an alien horror movie.

Once the drama of the moment settles down (everyone in the clinic always wants to take a peek), treating a warble is straightforward. Gently remove the larvae without rupturing it (otherwise the pet can have an anaphylactic reaction), flush out the cavity that remains with an antiseptic solution, and maybe prescribe antibiotics and pain relievers depending on the severity of the wound that’s left.

Warbles are disgusting, but not that big of a threat to pet health. Unfortunately, Cuterebra larvae don’t always restrict themselves to the skin. They have been found in nostrils, in the back of the throat, within eyes, and most seriously, in the brain.

These neurologic cases are the most difficult to deal with. The larvae migrate through the brain, damaging tissue and inciting inflammation as they go.

Since cuterebriasis is relatively rare, and cuterebriasis of the brain even more so, the first hurdle that must be overcome is reaching an accurate diagnosis (MRIs are best). Treatment with medications to kill the larvae and manage secondary inflammation, allergic reactions, and bacterial infections can be successful, but as you can imagine, the prognosis isn’t great when you’re trying to kill a large larva in a pet’s brain.

Dr. Jennifer Coates

Image: Hannamariah / Shutterstock

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