October 2003

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Diagnosis: Tungiasis

Histopathology: Histologic sections of the excision from the right sole of the foot show acral skin with underlying parts of an insect (Fig 2) including intestinal loops (Fig 3), eggs (Fig 4), and exoskeletal (Fig 4). These findings are consistent with tungiasis.

Discussion: Tungiasis, also known as chique, chigoe, and piroque is caused by the sand flea Tunga penetrans (or jigger or chigoe). The unfed adult T penetrans is among the smallest of fleas, measuring just 1 mm in length. The flea prefers warm, dry climates with a sandy terrain and is endemic to Central and South America, tropical Africa, the Caribbean, and India. This sand flea should not be confused with Trombicula alfreddugesi, the North American "chigger", which is a mite. Tunga penetrans is a poor jumper in comparison to other fleas, and thus most lesions occur on the feet. Both the male and female are blood-suckers with a wide-range of hosts including pig, fowl, and barefooted human. While the male leaves the host after a meal, the gravid adult female burrows into the soft skin, usually between the toes or near the nail bed. The female stops burrowing until the last abdominal segment is level with the skin surface forming an opening for the burrow. This opening is used for expulsion of feces and eggs. The head penetrates the dermis for feeding, and the egg-filled abdomen swells in size to about the size of a pea. Inflammation results and scratching facilitates the extrusion of eggs. Once the eggs are extruded, the female dies and the shriveled remains are usually expelled leaving a small ulcer at the site.

Clinically, common sites are between the toes, under the toenails, and along the medial border of the foot; occasionally the genitalia, perianal region, thighs, or hands may be affected. Early lesions appear as a black dot which is quickly surrounded by a ring of horny tissue with parasite visible. Itching, inflammation, swelling, and tenderness follow until necrotic tissue and the shriveled female are expelled leaving an ulcer. The differential diagnosis includes common flea and tick bites, creeping eruption, dracunculiasis, scabies, and myiasis. Possible complications involve secondary superinfection which can lead to cellulitis, gangrene, tetanus, or autoamputation of the toes. Treatment is removal of the flea. Care should be taken to remove all eggs and flea parts to prevent further inflammation. Our patient was treated with simple excision of the lesion with removal of all insect parts.

References:
1. Vennos E, Burke E, Johns C, and S Miller. Tungiasis. Cutis 1995 Oct 56(4):206-7.
2. Tungiasis, in: Clinical Tropical Dermatology, 2nd ed. Canizaris O, R Harman, ed. Blackwell Science 1992: 392-394
3. Zalar GL and RR Walther. Infestation by Tunga penetrans. Arch Dermatol Jan 1980. 116:80-81.

My thanks to Drs. Larry Wang and Peggy Chern for their assistance in the preparation of this case.