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Am Fam Physician. 2005;71(7):1262-1263

to the editor: A 64-year-old woman presented to our Urgent Care center for evaluation of an itchy lesion on her right medial lower leg, which had lasted for 15 days. She reported having an insect bite on this area of her leg while in El Salvador. Physical examination revealed a 2-cm violaceous nodule with “pinpoint” central opening and serosanguineous discharge. She was treated for an infected insect bite with cephalexin, 500 mg three times daily. After three days, she showed no improvement. This examination revealed a tiny dark object protruding from the central punctum. With careful lateral pressure and traction, a 2-cm–long botfly (Dermatobia hominis) larva was removed.

The botfly is found in the forests of Mexico, Central America, and South America. The gravid female fly usually captures a mosquito and sticks a packet of eggs into its abdomen. When the carrier insect feeds on a warm-blooded animal, the eggs hatch and the larva penetrates the skin. It feeds on host tissue and maintains a breathing pore in the skin.1 The larva then goes through the second and third stages of maturation. A third-stage larva measures 2 to 3 cm and has rows of spines around its abdomen.2 Between 27 and 128 days, the third-stage larva exits through the entrance wound and pupates in the soil for another 27 to 78 days. At that time, an adult fly emerges and lives two to 19 days without feeding. The entire life cycle lasts three to four months.3

Persons with botfly myiasis have a history of travel and an insect bite, and symptoms include itching or pain, and/or a feeling of movement in the skin. The typical lesion is a subcutaneous nodule with central pore and serosanguineous discharge. This lesion may be mistaken for an infected insect bite, boil, or inflamed epidermal inclusion cyst.

Attempts to suffocate and force extrusion of the larva with paraffin oil, petroleum jelly, bacon, chewing gum, beeswax, or polymyxin B ointment have been made with variable success. Gentle traction reinforced with lateral pressure also may be effective, as with our patient. Some physicians have used local lidocaine, chloroform, or a venom extractor.4 Physicians must be careful not to leave behind parts of larva. Surgery allows complete removal of larva and debridement of the cavity. Secondary infection is rare because of the bacteriostatic nature of the intestinal secretions of the larva. Using protective clothing and insect repellents should help prevent this and similar infections.5

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This series is coordinated by Kenny Lin, MD, MPH, deputy editor.

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