How to Treat Cuterebra in Pets

Close-Up Of A Dog While Burrowing In A Forest
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While not very common, Cuterebra larvae are parasites that are sometimes seen in pets. Knowing more about these little problems can help you get your pet the help it needs and hopefully prevent this parasite from causing future issues.

What Is Cuterebra?

Cuterebra larvae are the offspring of the bot fly and are also known as warbles. They are off-white in color and resemble large maggots. A pet with a Cuterebra larva is said to have cuterebriasis.

Female bot flies lay their eggs and when a pet comes in contact with the eggs, they infect the pet through the mouth or nostrils while the pet is grooming itself. The eggs may also enter a pet through an open wound. The larva hatches from the egg when inside the pet and migrates to a place under the pet's skin. It then creates a breathing hole and grows for about a month until it falls out of the pet to continue its life cycle.

Cuterebra, a genus of botfly
First instar larva of Cuterebra, a genus of botfly. Fly, parasite. Image courtesy CDC/Dr. George Healy Smith Collection / Gado / Contributor / Getty Images

Symptoms of Cuterebra in Pets

Cuterebra larvae can be difficult to find on a pet but the most obvious thing to look for is a swelling under the skin that also has a small hole in it. This swelling is often confused with a ruptured abscess but will actually be housing the growing Cuterebra. The larva may be visible through the opening as it pops up to breathe but is otherwise unseen until it falls out.

Aside from the swelling itself, several symptoms may be seen in pets with a Cuterebra infestation. Some pets will excessively lick at the swelling, cry when the swelling is touched, have discharge from the swelling, experience seizures, have excessive sneezing, be lethargic or depressed, develop blindness or an upper respiratory infection, or have an abnormally high or low body temperature. Outdoor cats are especially susceptible to Cuterebra but any animal that spends time outside is at risk.

Causes of Cuterebra

Pets will get a Cuterebra larva if they have come in contact with the bot fly eggs. This most commonly occurs with pets that spend a significant amount of time outdoors rolling on the ground or digging in the dirt where rodents live. Cuterebra naturally live in the environment just like other types of flies.

Treatment of Cuterebra

Veterinary attention is needed in order to remove a Cuterebra as it may require sedation or pain medications but in order to treat a pet with Cuterebra, the location of the larva must first be determined. This usually involves clipping the fur from the site of the swelling and locating the breathing hole. Once this is done and if the larva is not obvious, the hole can be covered with petroleum jelly for 10-15 minutes to make it easier to slide the larva out of the hole and restrict its breathing. The swelling should not be squeezed as this may crush the larva and cause further issues. Small forceps are used to grasp the larva and remove it in one piece but the breathing hole may need to be enlarged to facilitate removal. Anaphylaxis and reoccurring infections in the swelling site can potentially result in a pet if the larva is not removed intact or if pieces are left behind.

Once the Cuterebra is removed, the hole can be flushed with sterile saline. Occasionally your veterinarian will need to cut away some dead tissue from the swelling to allow the hole to properly heal. Antibiotics and anti-inflammatory medications are often prescribed but antihistamines, anti-parasitics, and other drugs to treat the symptoms of cuterebriasis may also be necessary. Some drainage from the swelling may occur but the hole should not be sutured shut.

treating cuterebra in pets illustration
Illustration: The Spruce / Yifan Wu

How to Prevent Cuterebra

The best way to prevent your pet from getting cuterebriasis is to keep it indoors but this is not always possible. If you have a pet that spends time outside, try and keep it away from rodents and the homes of rodents, especially during the late summer and fall months. If you notice your pet develops a swelling under the skin, you should get it checked out by a veterinarian as soon as possible to prevent serious symptoms of cuterebriasis from developing.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.