Diagnosis: Furuncular myiasis
Given the patient’s clinical presentation and travel history, furuncular myiasis infestation was suspected and confirmed by punch biopsy. Pathologic exam revealed botfly larvae in both wounds, consistent with the human botfly, Dermatobia hominis (FIGURE 2). Myiasis is not common in the United States but should be suspected in patients who have recently traveled to tropical or subtropical areas. Furuncular myiasis describes the condition in which fly larvae penetrate healthy skin in a localized fashion, leading to the development of a furuncle-like nodule with 1 or more larvae within it.
Dermatobia hominis is the most common causative organism for furuncular myiasis in the regions of the Americas. Patients typically present with 1 lesion on an exposed part of the body (eg, scalp, face, extremities). The lesions typically contain a central pore with purulent or serosanguinous exudate.1 Upon dermatoscopic inspection, one can often see the posterior part of the larva or the respiratory spiracles, which look like tiny black dots on the surface of the wound. The organism may also be indirectly viewed through respiratory bubble formation within the exudate.1,2 Diagnosis is confirmed by extracting the larvae from the wound and having the species identified by an experienced pathologist or parasitologist.
Mode of transmission
Phoresis is the name of the process by which Dermatobia hominis invades the skin.3 The female fly lays her eggs onto captured mosquitos using a quick-drying adhesive. The eggs are then transferred to the host by a mosquito bite. The host’s body heat induces egg hatching, and the larvae burrow into follicular openings or skin perforations. This leads to the development of a small erythematous papule, which can further lead to a furuncle-like nodule with a central pore that allows the organism to respirate. When ready to pupate, the larvae work their way to the skin surface and drop to the soil, where they can further develop. After pupation, the fly hatches and develops into an adult, and the cycle repeats.
Common infectious and inflammatory lesions are in the differential Dx
The differential diagnosis includes bacterial abscess, exaggerated arthropod reaction, and ruptured epidermal cyst. With our patient, the travel history and unique exam findings led to the suspicion of myiasis.
Bacterial abscess is likely to have more notable purulence with response to appropriate oral antibiotics and no bubbling phenomenon on exam. It is also unlikely to be present for 1 month without progressive worsening.
Continue to: Exaggerated arthropod reaction