Cuterebra Infestation in Dogs and Cats

What are Cuterebra (warbles)?

Cuterebra infestation, commonly called warbles, is a condition characterized by the presence of Cuterebra larvae under the skin of companion animals like dogs and cats. Though not as common as other external parasites, it is still e\qually important and needs to be treated and addressed accordingly.

Cuterebra is the scientific family name for the group of botflies commonly found in North America. There are about 26 species of botflies under this family, found in different regions of the U.S. and Canada. This insect is also found in certain areas in Central and South America.

Adult Cuterebra flies are not parasitic. They are large flies that resemble bees in appearance but do not bite or feed on animals. What makes them parasitic is their life cycle, and how they replicate and develop from egg to adult flies. Adult botflies are often harmless to animals like dogs and cats, but their larva is considered opportunistic parasites to these animals.

How do Cuterebra larvae infect dogs and cats?

As mentioned, adult Cuterebra flies do not usually cause medical problems in dogs and cats. It’s the larval stage of these flies that causes infestation and skin problems for our furry friends. Cuterebra botflies have an indirect life cycle, requiring an intermediate host to complete its cycle from an egg to an adult fly.

Female Cuterebra flies need a dark, warm, and enclosed environment to lay their eggs in. The conditions that these environments provide allow for the eggs to hatch and produce larvae. They usually lay their eggs around animal nests, burrows, or along runways of hosts and deposits around 15 eggs per site. A female Cuterebra botfly can lay up to 2,000 eggs in her lifetime.

Infestation occurs when animals pass through areas where eggs are deposited. The warmth from the host’s body triggers these eggs to hatch and the larva enters the host through normal body openings such as the nose or mouth. Occasionally, Cuterebra larvae enter through open wounds.

Most species of Cuterebra flies are host-specific and do not cause an infestation in animals other than their natural hosts. However, there are certain species, like the rabbit Cuterebra, that are considered opportunistic parasites and can penetrate other animals like dogs and cats.

Once the larva penetrates the host’s skin, it migrates to various locations on the body depending on the Cuterebra species. They develop into mature larva while under the host’s skin and exit in about 30 days. The mature larva falls onto the ground and pupates, where it will eventually transform into an adult botfly, the duration of which is dependent on the species and environmental conditions.

Symptoms of Cuterebra Infestation in Dogs and Cats

The most common sign of Cuterebra infestation in dogs and cats is the presence of soft, well-demarcated swelling under the skin. Lesions associated with Cuterebra larval infestation are commonly seen during late summer or early fall, the time when larvae grow bigger and cause swelling around 1 cm in diameter.

Skin lesions caused by Cuterebra larvae are often seen around the neck, trunk, and head area. Since dogs and cats are not the natural hosts of these botflies, larvae occasionally migrate to uncommon locations such as the head, brain, nasal passages, and eyelids.

Pain is usually present on affected areas of the skin, and the affected animal can react in pain when the lesions are touched. Cats with migrating Cuterebra larvae under their skin often groom excessively and aggressively. In worse infestations, a thick discharge may be seen in the skin lesions.

Neurological signs like seizures and tremors are seen in cases where the larva have migrated towards the host’s brain. Respiratory signs like sneezing, coughing, and respiratory discharges can be seen in cases of respiratory larval migration. Occasionally, affected animals will have a fever.

The presence of Cuterebra larva is a definitive sign of infestation. Diagnostic imaging like CT-scan or ultrasound may be needed for cases of uncommon larval migration. Proper identification is necessary for a definitive diagnosis.

How are pets with Cuterebra infections treated?

The recommended treatment for Cuterebra infestation in dogs and cats is manual removal of the larvae. This is done by carefully exploring skin lesions for the presence of Cuterebra larvae, and manually removing them using surgical forceps. Sedation or anesthesia may be needed to successfully remove larvae in most dogs and cats, especially if the infestation is severe.

Manual removal of larvae that have migrated in uncommon places like the respiratory tract is more difficult to perform, and surgery is often needed to facilitate complete removal. It’s important to not squeeze or crush the larvae during extraction from the host’s body to prevent the risks of secondary bacterial infection.

Even after the removal of Cuterebra larvae from the host, medical management is often necessary to control the inflammation and pain from the migration. Systemic antibiotics may be indicated if there’s a presence of secondary infection. Lesions are regularly disinfected after the removal procedure and are allowed to heal through granulation.

Unfortunately, surgical removal of larvae that have migrated to the brain or the nervous system of the affected animal is extremely difficult to perform. The use of an anti-parasitic medicine called ivermectin, coupled with diphenhydramine and corticosteroids, is usually recommended in cases of CNS Cuterebra infestation.

If you’ve observed skin lesions in your dog or cat similar to the signs described above, it’s best to bring your pet to the nearest veterinarian for proper assessment and treatment.

Read more:

Common Skin Parasites in Cats

Common Skin Parasites in Dogs

Symptoms and Treatment of Mites in Dogs

Need to speak with a veterinarian regarding dog and cat parasites or another condition?

Click here to schedule a video consult to speak to one of our vets. You can also download the FirstVet app from the Apple App Store and Google Play Stores.