HOW TO Treat Your Dog for Botfly (Maggot) Infection

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CuterebraCuterebra, or botflies, are often found in rodents and rabbits in North and South America. After laying eggs on blades of grass, or in nests, they proceed to hatch and release maggots that catch onto the skin of a passing host.

According to, “The small maggots enter a body orifice, migrate through various internal tissues, and ultimately make their way to the skin, where they establish themselves within 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.”

“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.”

What Can Cause Botfly Infection? says, “In most cases, the larvae migrate to areas just under the skin on the head, neck or trunk of the animal. In dogs, cats and ferrets, who are not the usual hosts of this parasite, the larvae may also migrate to the brain, eye, eyelids or throat.”

Cuterebra larva can grow up to 1 inch long and ½ inch in diameter. If the parasite has led to irreversible neurological damage, the prognosis will be poor and euthanasia may be the only option. mentions, “The most likely places for your dog to acquire this parasite are in environments where the botfly flourishes: grassy areas where there are adequate populations of rodents and rabbits. Even dogs without access to the outdoors, such as newborn puppies, can be infected from larvae brought home on the mother’s fur.”

How ToWhat are the Symptoms of Botfly Infection?

According to, “The swelling is commonly observed by the owner, who may think it is a small tumor. These swellings usually appear in the late summer and fall. When the animal is examined by a veterinarian, the area over the swelling is clipped, and the telltale opening will be seen. In some cases, the larva can be seen through the hole. Younger larvae are gray in color and have short rows of spines. Mature larvae are dark in color, and covered with spines.” recommends that you take your pooch to the vet immediately if you start to notice these symptoms:

Respiratory symptoms:

i Love Dogs Cough

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Neurological symptoms:

i Love Dogs Dizziness

i Love Dogs Circling

i Love Dogs Paralysis

i Love Dogs Blindness

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Opthalmic symptoms:

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Skin symptoms:

i Love Dogs 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. also mentions, “Most cuterebra larvae are found on the head and neck of dogs. Sometimes, the larvae migrate abnormally and end up traveling through the brain. This results in fatal brain and nervous system abnormalities, such as seizures. Typically, one larva is found per breathing hole.”

How is a Botfly Infection Diagnosed?

According to, “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:

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If your dog has lesions on his eye, there may be a more serious parasitic larval infestation that can lead to permanent blindness, and will need to be ruled out by your vet.

How is a Botfly Infection Treated? states, “Extreme care is used to remove the larvae. An incision is made through the skin, and the larva is carefully removed. If the larva is cut or crushed, the animal may develop an anaphylactic reaction or severe skin irritation at the site. The ‘pocket’ that was formed around the larva is cleaned and flushed, and a topical antibiotic ointment may be prescribed. The thickening of the skin takes considerable time to resolve.”

If you don’t surgically remove the larva, it will grow and eventually break out of the skin and fall out, starting its life cycle again.

Check out this video of i Love Dogs’ Ask A Vet, Dr. Patrick Mahaney extracting a bot fly larvae from a homeless dog’s eye during an Amazon Cares Vets Abroad Trip to Peru sponsored by i Love Dogs, Inc.

botflyHow Can I Prevent a Botfly Infection ? reports, “There does not seem to be any prolonged immunity to infestation; a dog can develop skin lesions 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 may kill the maggots before they have time to gain access to an orifice for entry.”

 Try to limit access to rabbit and wild rodent nests or burrows, but if this isn’t possible, try to frequently monitor your dog’s skin for cuterebra larva. warns, “Home removal of cuterebra larva is not recommended due to the potential for serious reactions. After removal, the wound should be kept clean and allowed to heal.”

Find A Vet HOW TO articles are intended for informational purposes only. You should always consult with your veterinarian about any health issues affecting your dog.

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Kara Ogushi

Contributing writer Kara Ogushi is a pet mom to two dogs and five rabbits. When she isn't writing travel tips for pooches, she's exploring new ways to share and create media.

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