ARTICLE
Case report
A 35-year-old Caucasian female presented with a nodular lesion on her
right thigh next to the inguinal region (Fig. 1a).
The lesion appeared about three weeks previously, and it had slowly enlarged.
A topical antibiotic had been given for about ten days without any improvement.
The patient had made a trip to Iguazù falls and Paranà,
in Brazil, about six weeks earlier, without noticing any symptom at that
time. During the trip she was wearing shorts. On physical examination
a nodular red lesion, ulcerated in the center, was observed on the right
inguinal region. The lesion was painful and indurated, surrounded by an
erythemato-edematous halo.
What's your diagnosis?
Diagnosis: cutaneous myiasis due to dermatobia
hominis
A general examination revealed a groin lymphoadenopathy. Laboratory
findings were all within normal ranges except for a slight increase in
white blood cell count (9,500 mm3). Movement within the pore
was noted (Fig. 1b). The entire lesion was surgically
removed under local anaesthesia with xylocaine. A single oval self-moving
larva was extracted from the tissue. The maggot was classified as a stage
III Dermatobia hominis larva (Fig. 2). The surgical
wound progressively healed in one week without any complication.
Comments
Myiasis is the infestation of body tissue in living vertebrates by the
Diptera larvae occurring in cutaneous myiasis (furuncular or creeping
eruption), wound myiasis and myiasis of cavities and viscera [1, 2].
Cutaneous myiasis due to Dermatobia hominis is a common disease in endemic
and tropical regions. With the increase of international travel, myiasis
can be observed anywhere. All the clinical cases due to Dermatobia hominis
reported in Europe and Asia are imported from Central and South America
[3-6].
Dermatobia hominis lives in hot and humid forests of Central and South
America, as a parasite of cattle and other domestic stocks, accidentally
of men. The adult fly, grey-brownish coloured, can grow up to 2 cm long.
It has a peculiar life cycle. When the female is ready to oviposit, she
captures a blood-sucking arthropod, generally mosquitoes, stable or house
flies, and lays the eggs on the abdomen of the carrier insect (phoresis).
After the mosquito has bitten a mammalian, the warmth of the host provides
the stimulus for the eggs to hatch [7]. The larvae penetrate the skin
through the site of the bite or the hair follicles. They are able to breath
through their tail via the posterior spiracles. The whole development
takes place in about 5-10 weeks through their second and third larval
stages in the subcutaneous tissue. Finally, the larvae emerge from the
skin and fall to the ground. Under favourable conditions the larvae are
able to pupate in about 2-4 weeks.
In man every part of the body can be involved. The nodule can be single
or multiple, generally painful. Itching is common. The patient sometimes
senses movement under the skin [8].
Removal of the larva is the treatment of choice, followed by administration
of systemic antibiotics in case of an associated infection. Several methods
of dealing with the larva have been employed, especially in the regions
where traditional surgical excision is not practical. In endemic countries
toxic substances such as tobacco or ashes or sap of Thevetia ahouai
have been applied to the surface of the lesion. Paraffin may be smeared
over the opening and left in place for up to 24 hr in order to asphyxiate
the larva and promote expulsion [9]. Hydrocolloid dressing followed by
forceps removal is usually curative. Removal must be done extremely carefully
because of the easy rupturing of the larvae that anchor themselves in
the host tissue by spines [3]. Surgical extraction under local anaesthesia,
followed by an irrigation of the cavity to remove dead tissue and accelerate
healing, is an alternative technique. We treated our patient with surgical
removal of the entire lesion in order to avoid inadvertently leaving larva
remnants in the wound. The surgical extraction was also the only therapy
accepted by the patient.
The diagnosis of myiasis is easily overlooked in Europe because of its
rarity. The more frequent trips to tropical and subtropical areas led
us to consider this diagnosis for a non-follicular furuncular swelling
on exposed skin in a patient who had been in endemic areas [10].
References
1. Elgart ML. Flies and myiasis. Dermatol Clin 1990; 8:
237-44.
2. Noutsis C, Millikan LE. Myiasis. Dermatol Clin 1994;
12: 729-36.
3. Gewirtzman A, Rabonivitz H. Botfly infestation (myiasis) masquerading
as furunculosis. Cutis 1999; 63: 71-2.
4. Desruelles F, Delaunay P, Marty P, Del Giudice P, Mantoux
F, Le Fichoux Y, Ortonne JP. Myiasis caused by Dermatobia hominis after
an organized tour in Amazonia. Presse Med 1999; 28: 2223-5.
5. Veraldi S, Gorani A, Suss L, Tadini G. Cutaneous myiasis caused
by Dermatobia hominis. Pediatr Dermatol 1998; 2: 116-8.
6. Taniguchi Y, Yamazaki S, Ando K, Shimizu M. Cutaneous myiasis
due to Dermatobia hominis in Japan. J Dermatol 1996; 23: 125-8.
7. Jelinek T, Nothdurft HD, Rieder N, Loscher T. Cutaneous myiasis:
review of 13 cases in travellers returning from tropical countries. Int
J Dermatol 1995; 34: 624-6.
8. MacNamara A, Durham S. Dermatobia hominis in the accident
and emergency department: "I've got you under my skin". J Accid Emerg
Med 1997; 14: 179-80.
9. Pallai L, Hodge J, Fishman SJ, Millikan LE, Phelps RG. Case
report: myiasis-the botfly boil. Am J Med Sci 1992; 303: 245-8.
10. Kahn DG. Myiasis secondary to Dermatobia hominis (human botfly)
presenting as a long-standing breast mass. Arch Pathol Lab Med
1999; 123: 829-31.
 
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Figure 1a. A single
nodular lesion, about 4 cm large, in a furuncular pattern with inflammatory
reaction on the right inguinal region.Figure 1b. The tail of
the larva emerges from a small central ulceration. |
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Figure 2. An intact
larva of Dermatobia hominis, 18 mm long and 6 mm large, at stage III.
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