Myiasis is an infestation of the skin and, less frequently, other body sites by developing larvae (maggots) of a variety of fly species (myia is Greek for fly) within the arthropod order Diptera. It affects humans and other mammals. Worldwide, the most common flies that cause the human infestation are Dermatobia hominis (human botfly) and Cordylobia anthropophaga (tumbu fly).

Myiasis is uncommon in the United States and other non-tropical locations, and any cases reported are usually imported cases of myiasis from travelers returning from tropical destinations. That was the circumstance in the case depicted here.

The pathophysiology of the human infection differs depending on the type of fly and its mode of infestation.

Dermatobia hominis (human botfly) - Furuncular myiasis This type is endemic to tropical southeast Mexico, South America, Central America, and Trinidad. The life cycle of the botfly is unique, as the female, egg-bearing fly catches a blood-sucking arthropod, usually a mosquito (although 40 other species of insects and ticks have been reported), midflight and attaches her eggs to its abdomen. When the mosquito takes a blood meal from a warm-blooded animal, the local heat induces the eggs to hatch and drop to the skin of the host and enter painlessly through the bite of the carrier or some other small trauma.

Cordylobia anthropophaga (tumbu fly) - Furuncular myiasis This type is endemic to sub-Saharan Africa. The females lay their eggs on dry, sandy soil or on damp clothing hung out to dry. The eggs hatch in 1-3 days and the larvae can survive near the soil surface or on clothes for up to 15 days waiting for contact with a suitable host. Activated by heat, such as the body heat of the potential host, they can penetrate the unbroken skin. A pruritic erythematous papule develops within 24 hours of penetration, enlarging to 1-3 cm in diameter and almost 1 cm in height. These lesions can be painful and tender. Each has a central punctum from which serosanguineous fluid may be discharged. Lesions may become purulent and crusted; the movement of the larva may be noticed by the patient. The tip of the larva may protrude from the central opening (punctum), or bubbles produced by its respiration may be seen. Eventually fully developed larvae emerge from the host in 5-10 weeks and drop to the ground, where they pupate to form flies in 2-4 weeks.

In nasopharyngeal myiasis, the nose, sinuses, and pharynx are involved. Ophthalmomyiasis affects the eyes, orbits, and periorbital tissue, and intestinal and urogenital myiasis involves invasion of the alimentary tract or urogenital system.

Myiasis is a self-limited infestation with minimal morbidity in most cases. The major reasons for treatment are reduction of pain, cosmesis, and psychologic relief. Once the larva has emerged or has been surgically removed, the lesions rapidly resolve. Obstructing the central punctum with a covering material cuts off the oxygen supply to the larvae and may encourage them to emerge. Ivermectin has been used to treat non-cutaneous forms of Myiasis. 

Descriptive text extracted from Medscape.com. Authors Adam B. Blechman, MD and Barbara B. Wilson, MD. Images A, B, E, F contributed by Nancy Shina, FNP-C and RoseAnn Tracy