Barclay is an 11-year old miniature Schnauzer who presented to our hospital to have a ‘lump’ assessed. On physical examination there was a firm, painful swelling that measured 3cm X 3cm on the right lateral flank. There was a small opening in the center of the ‘lump’ with purulent and bloody discharge present.
The affected area was shaved and lidocaine (a local anesthetic) was administered under the skin. The small opening was then made larger using a pair of surgical hemostats. At that time we noted ‘movement’ under the skin and we were soon able to visualize a live larva. A small pair of forceps was used to remove the larva – it is important not to squeeze the lesion because this may rupture the larva and lead to a chronic foreign body reaction and secondary infection. The area was thoroughly flushed with sterile saline and antibiotics were administered to treat the infected area.
Adult female Cuterebra flies lay eggs on blades of grass or in nests or burrows of rodents (eg. rats, squirrel, chipmunks) or lagomorphs (eg. rabbits, hares). A female fly may lay up to 5-15 eggs per site and over 2,000 eggs in her lifetime. The eggs hatch and crawl onto the skin of the passing animal host. The small larvae enter the host through the mouth or nares during grooming or through an open wound. The larvae then migrate through various internal tissues until they form a warble, a subcutaneous area under the skin containing the larva. The larva communicates with the outside via a breathing hole in the skin.
Cuterebra lesions are most common in the summer and fall. Dogs and cats usually present with a firm, painful swelling of the skin with a hole in the center as Barclay did. This is considered the dermatological presentation involving the skin and underlying tissue only. The larva can migrate to the respiratory, neurologic or ophthalmic systems causing signs like coughing, paralysis or blindness. These are more severe presentations with different treatment options.
Barclay returned for a follow-up examination in 7 days. The swelling had decreased and the skin in the area had granulated in and healed.