Botfly Infestation

March 1, 2007

A painful, indurated, erythematousswelling arose on the left wrist of a62-year-old man who had recentlyvisited Guatemala. Initially, the lesionwas about 2 cm in diameter andhad 2 central openings that drainedserosanguinous fluid on pressure.The patient denied trauma to thearea or insect bites.


A painful, indurated, erythematous swelling arose on the left wrist of a 62-year-old man who had recently visited Guatemala. Initially, the lesion was about 2 cm in diameter and had 2 central openings that drained serosanguinous fluid on pressure. The patient denied trauma to the area or insect bites.

A 7-day course of oral amoxicillin/ clavulanate was prescribed, followed by a 14-day course of cephalexin; however, the erythema diminished only slightly. Results of a complete blood cell count and serum biochemistry profiles were normal.

When the patient returned for a follow-up visit, he brought 2 larvae that had exited the lesion spontaneously after continuous digital expression of the site. Microscopic examination of the specimens confirmed the diagnosis of myiasis caused by Dermatobia hominis (A). After removal of the larvae, the lesion remained erythematous and painful, and the 2 central apertures became slightly necrotic (B).

The lesion was excised and drained. Gatifloxacin was started for a secondary bacterial infection. After 4 weeks, the patient's wrist had healed.

The human botfly is endemic to Central and South America. Typically, its eggs are deposited on mosquitoes, which bite the human host. The eggs penetrate the skin via the bite or a hair follicle and continue their life cycle in the subcutaneous tissue.1 The host may experience pruritus and pain at the site and may even feel the larva move under the skin.2 After about 6 weeks, the larva exits the skin through a punctum.

The larvae can be removed by manual extraction or by surgical excision. Occlusion of the punctum with petrolatum (or a similar substance) may induce the parasite to exit the skin to avoid asphyxiation.

REFERENCES:1. Lawson RD, Rizzo M. Digital infestation with the human bot fly. J Hand Surg [Br]. 2005;30:490-491.
2. Adams DW, Cooney RT. Excision of a Dermatobia hominis larva from the heel of a South American traveler: a case report. J Foot Ankle Surg. 2004;43:260-262.

(Case and photographs courtesy of Micah Chan, MD, MPH, and Suresh Ramamurthy, MD, of University of Wisconsin Hospitals and Clinics, Madison.)