Cuterebra Parasitism

Key Points

Cuterebra larva can infest the body of pets such as dogs, cats and ferrets

A painful swelling with drainage is common to this problem

Surgical removal of the larva is the treatment of choice



Cuterebra flies in themselves are innocuous and do not bite or sting. They are very large flies that lay eggs around the openings of animal nests, borrows, or on stones or leaves. Typically, only 15 eggs are laid at a time, but a total of more than 2000 eggs are laid by a single fly in her lifetime. Dogs, cats, and ferrets can be infested by coming in contact with the eggs of the cuterebra. Heat from the pet’s body stimulate the eggs to hatch. The larva enter the body via the nose or mouth and migrate to the subcutaneous tissue (fat layer beneath the skin), grow and create a breathing pore through the skin. Within 30 days the larva exits the skin, falls to the ground, and develops into a pupa. From there the pupa emerges as a fly.



Cuterebra infestation is typically seen in the summer or fall. A swelling (mass) is present most commonly over the head, neck, or trunk. Uncommon locations for a cuterebra infestation include the head, brain, nasal passages, pharynx, and eyelids. Matting of hair is found over the skin lesion due to secondary bacterial infection or inflammation associated with the parasite, and the site is painful when palpated. Cats tend to groom affected areas excessively. A small pore is typically identified over the skin swelling, which corresponds to the breathing pore. Some affected animals have a fever and are systemically ill (will not eat and are lethargic).



The skin swelling should be surgically explored to remove the cuterebra. An incision is made to enlarge the breathing hole, yet care is taken to prevent puncture of the worm with the sharp surgical instruments. The cuterebra is grasped and is extracted with forceps. The skin must not be squeezed in an effort to extrude the cuterebra, as this could result in rupture of the worm’s body with subsequent chronic foreign body reaction and secondary infection. Less commonly, rupture of the worm within the pet’s body could cause a severe acute allergic reaction (anaphylaxis) that may result in death of the patient. The wound is flushed with saline.


Following surgical removal of the cuterebra, a chronic recurrent abscess may form. If this occurs, surgical excision of the area is performed to resolve the problem. In general, complications are uncommon.

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