Botflies (Cuterebriasis) in Dogs

Published on
Last updated on
4 min read

Key takeaways

Cuterebriasis is a parasitic infestation caused by the larvae of Cuterebra species (Botflies). Botflies are typically parasites of rabbits and other rodents, but sometimes they may infect dogs and other pets. 

  • Dogs come in contact with the parasite by passing through infested areas
  • Larvae penetrate the host’s body through the mouth, nose, or open wounds
  • In most cases, cuterebriasis manifests with skin lesions caused by the maggots hatching within the skin
  • In severe cases, the larvae might migrate through other tissues, leading  to complications in the eyes, lungs, and brain
  • The diagnosis consists of identifying the larvae within a skin swelling
  • Other tests might include diagnostic imaging and bloodwork, in cases where the maggots migrated through other organs
  • Treatment involves the removal of maggots from the skin and, in some cases, prescription of medications such as antiparasitics and steroids
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A closer look: Botflies (Cuterebriasis) in Dogs

Species of botfly are found throughout North America. They are most active in the spring and summer. Species of botflies may infest any type of mammal. The Cuterebra genus are most commonly hosted by rodents and rabbits, but dogs sometimes come into contact with them in outdoor areas where infested rodents and rabbits live.

Usually, botflies infestation causes nothing more than discomfort for the patient, although severe manifestations are possible, especially if larvae migration affects the nervous tissues or other organs. Dogs are abnormal hosts for botflies so developing the condition is rare, with possible peaks during the summer and fall seasons.

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Risk factors

Botfly infestation in dogs is rare. It is more likely to occur in areas and times of year when botflies are most active. There are no particular risk factors for specific dogs, but those with active outdoor lifestyles in rodent habitats are more likely to be exposed to botflies.

When infestation occurs, it usually only affects the skin. Left untreated, or in cases where the parasite load is very high, the larvae may migrate to other tissues, causing more severe symptoms.

Larvae can also migrate through the lungs, causing symptoms such as coughing and difficulty breathing.

Pain in the affected area is variable and is often associated with secondary infections.

Possible causes

The infestation is caused by botfly eggs that penetrate the host’s body through the mouth, nostrils, or open wounds. Botflies do not lay their eggs directly on dogs, rather they choose areas normally frequented by their natural host (rabbits and rodents) or around their nests. Dogs usually come in contact with the parasite by passing through a contaminated area, allowing botfly eggs to transfer onto their skin or face.

Main symptoms

The most characteristic sign of cuterebriasis is a soft swelling with distinct borders, which might be mistaken for an abscess. These swellings are most common on the head, neck, or trunk. Other symptoms include matted hair and visible bots (maggots) protruding from the swelling.

Testing and diagnosis

In cases of skin manifestation, the diagnostic process is straightforward and involves identifying the bot within a skin lesion.

If the larvae migrated through other organs, bloodwork and diagnostic imaging, such as ultrasound, MRI, and CT scanning, might be necessary for a definitive diagnosis.

Steps to Recovery

Treatment involves removal of the maggots from the skin followed by wound cleaning and supportive care. Other therapies include the prescription of anti-parasitic medications or steroids for infections affecting other organs.

Prognosis varies according to the form of cuterebriasis affecting the patient. The cutaneous form has a good prognosis and the patient generally recovers fully with treatment. The neurological form has a poor prognosis as it may affect sight and might lead to seizures or other serious symptoms.


To avoid contact with parasites it is suggested to prevent dogs from wandering in at-risk areas, such as near dens or burrows, especially during the period of higher presence of botflies. Routine deworming protocols are also highly suggested as they may prevent maggots from developing or kill them before they enter the dog.

Are Botflies (Cuterebriasis) in Dogs common?

Botfly infestation in dogs is rare.

Typical Treatment

  • Removal of maggots from the skin
  • Medications such as anti-parasiticsand/or steroids


Karen A. Moriello , DVM, DACVD - Writing for Merck Veterinary Manual
Lindsay A. Starkey DVM, PhD, DACVM (Parasitology) - Writing for Today's Veterinary Practice
No Author - Writing for Companion Animal Parasite Council

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