What does a warble look like on a cat

August 07, 2014 / Cat's Meow / 1 Comment

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. 

Cutere-what?

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.

Life Cycle

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.

Prevention

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

Botflies, flies that are of the genus Cuterebra, are found in the Americas, where they are obligatory parasites of rodents and rabbits. The botfly proliferates by laying eggs on blades of grass or in nests, where they hatch, releasing maggots that crawl onto the skin of passing animals. The small maggots then enter a body orifice, migrate through various internal tissues, and ultimately make their way to the skin, where they establish themselves within the skin, creating a warble (a small lump in the skin). The mature maggots, which may be an inch long, then drop out of the rodent or rabbit host and pupate in the soil.

Cats become infected with a botfly larva when they come into contact with a blade of grass that has a maggot on it. The movement of the cat against the blade of grass stimulates the maggot to crawl onto the cat. The maggot then crawls around on the cat until it finds an orifice in which to enter.

In the northern U.S. the disease is seasonal, with most cases occurring in late summer and early fall when the adult flies are active. Seasonality is less determined in areas with warmer temperatures, where flies are active through longer periods of the year.

Symptoms and Types

Cuterebra infection may be detectable by warbles below the surface of the skin, or your cat may show signs associated with the larvae migrating within their tissues. Symptoms can include respiratory signs, neurological signs, opthalmic (eye) lesions, or the aforementioned maggots under the skin.

Respiratory symptoms:

• Cough
• Fever
• Shortness of breath

Neurological symptoms:

• Dizziness
• Circling
• Paralysis
• Blindness
• Lying down

Opthalmic symptoms:

• Lesions (caused by the larvae in the eyeball)

Skin symptoms:

• Lump in the skin containing the maggot, also called a warble; there will be a raised opening in the lump so that maggot may breathe

Causes

The most likely place for your pet to acquire this parasite is in an environment where the botfly flourishes: grassy areas where there are adequate populations of rodents and rabbits. But, even pets without access to the outdoors, such as newborn kittens, can be infected from larvae brought home on the mother's fur.

Diagnosis

Your veterinarian will want to consider the following conditions before positive diagnosis of a cuterebra infection is made. Respiratory symptoms will be evaluated for allergies, and for other possible parasites, like lungworms or other migrating worms that use the respiratory tract as a passage. Conditions that might produce similar neurological symptoms, but are of graver consequence, will need to be ruled out before treatment is given for a cuterebra infection. These conditions include rabies, distemper, and heart worms. If your cat has lesions on the eye, there may be a more serious parasitic larval infestation, one that can lead to permanent blindness, that also needs to be ruled out.

The clearest indication of a cuterebra infection is, of course, a warble under the skin, in which case your veterinarian will be able to quickly determine whether it is the botfly.

Treatment

If the maggot is at the end of its migratory stage and has settled into a spot on the body, such as under the skin, eyes, or nose, your veterinarian will be able to remove it safely. Manifestations of lung migration may be alleviated by corticosteroids. If the parasite has led to irreversible neurological damage the prognosis will be poor and euthanasia may be the only option.

Your veterinarian will probably prescribe a broad-spectrum anti-parasite medication, which should kill maggots still in the migrating stage. A corticosteroid treatment will be given before administering the medication. The anti-parasite medication can be administered either to alleviate the signs caused by maggots suspected of migrating in the lungs, or to kill larvae in other tissues, including the central nervous system.

Prevention

There does not seem to be any prolonged immunity to infestation; an animal can develop skin lesions due to botfly infestation for several years in a row. Application of monthly heartworm preventives, flea development control products, or topical flea and tick treatments may either prevent the maggots from developing in the dog or cat, or may kill the maggots before they have time to gain access to an orifice for entry.

By Jennifer Coates, DVM

You’re petting your cat and you feel a lump. What do you do? Take a closer look of course. You carefully part the fur and now you can see a little hole in the skin too, but wait, it looks like something’s in there … and it’s moving! After you get over your disgust, you’re bound to wonder what could possibly be wrong with your cat. Chances are, you’re dealing with a botfly. Let’s take a look at what botflies are and how they affect cats.

What is a Botfly?

Botflies (also known as Cuterebra) are found all over most parts of North America, although the northeastern United States is a botfly hotspot. Adult botflies (large, fuzzy flies that look a little like bees) lay their eggs near the entrances to their host animal’s burrows (rabbits, rodents, etc.). These eggs hatch and larvae emerge when a potential host is nearby. The larvae grab on to the animal’s fur and then enter the body through any opening (like the nose, mouth or anus). Once inside, they migrate through the body until they arrive in the tissues under the skin. Once there, they make a small hole so they can breathe, continue maturing and eventually emerge and fall to the ground where they become pupae and then adult flies.

How Do Cats Get Botflies?

Most species of botfly have developed a parasitic relationship with one type of mammal, but occasionally they get confused. That appears to be what happens with cats. Since cats love to hunt small mammals, they are attracted to their burrows. While they are poking around there, a botfly larva may mistake them for a rabbit, for example, and hop aboard. Once on a cat, the botflies proceed through their lifecycle as if they were infesting their host species even though it appears that the adult flies that result are not able to reproduce due to this mistake.

Symptoms of a Botfly Infestation

Feline botfly infestations are quite common. All ages and sexes of cats can be affected as long as the individual has access to the outdoors. In northern regions, most cases are seen in the late summer and early fall since botflies cannot be active in the winter. Cases can occur year-round in parts of the country that do not experience cold winters.

The most common symptoms of a botfly infestation is the presence of a lump under the skin accompanied by a small hole through which a thin, relatively clear liquid drains. Cats may lick or scratch at the area causing hair loss and irritating the surrounding skin. Occasionally, migrating larva can end up in unusual locations within the body including the eye, nostrils, throat, chest and brain. Symptoms will depend on what part of the body is affected. For example, the neurologic disease feline ischemic encephalopathy is caused by Cuterebra larvae migrating through the brain.

How to Treat Warbles in Cats

The lump under the skin of a cat infested with a botfly larva is called a warble. In order to get rid of it, you’ll need to make an appointment with your veterinarian. He or she can remove the botfly larva and recommend any follow up care that might be needed to ensure that your cat heals uneventfully. Veterinarians can remove warbles in a number of different ways, including:

1. Anesthetizing the cat, surgically widening the opening in the skin and removing the botfly with a pair of hemostats or tweezers.
2. If the opening in the skin is large, the botfly is small and the cat is cooperative, surgery may not be necessary. The veterinarian may sedate the larva with an anesthetic and then pull it out.
3. Alternatively, some doctors will place a liquid or salve into the hole that eliminates the larva’s ability to breathe. The botfly will usually soon start to emerge at which point it can be grasped and pulled out.

The most important part of treating warbles in cats is to make sure that the entire botfly larva is remove without significant damage to its body. Crushing it or leaving a piece behind can lead to chronic infections or a potentially fatal allergic reaction called anaphylaxis.

How to Prevent Warbles in Cats

The easiest way to prevent warbles is to stop your cat from going outside. If this is not feasible, it is possible that treating your cat monthly with a parasiticide like ivermectin (Heartgard), fipronil (Frontline), imidacloprid (Advantage), or selamectin (Revolution) might prevent warbles in cats even though definitive research has not yet been done.

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