Dermatology Online Journal

Stowaways with wings: Two case reports on high-flying insects
Ronni Wolf MD, Edith Orion MD, and Hagit Matz MD
Dermatology Online Journal 9(3): 10

The Dermatology Unit, Kaplan Medical Center, Rechovot, Israel. wolf_r@netvision.net.il

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Abstract

More people than ever before are trasversing continents, either for business purposes or on holiday. Because 3-10 percent of these travelers experience skin, hair, or nail disorders related to these trips there is an increasing likelihood that Western physicians will be expected to treat exotic conditions imported from different countries.
Tungiasis and furunculoid myiasis are two typical disorders of intertropical regions. They represent nuisances induced by the presence of arthropod larvae or eggs in the skin. We describe a case of tungiasis, caused by the sand flea Tunga penetrans (TP), and a case of myiasis, caused by Dermatobia hominis (DH), and briefly discuss the epidemiology, biologic life cycles, vectors, reservoirs, and clinical presentations of these parasites.

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The increase in rapid international air travel to the tropical areas has produced a rise in imported diseases that were formerly restricted to the equatorial zones. Physicians in Western countries are increasingly encountering patients with a variety of parasitoses and now must be familiar with the clinical symptoms and relevant exposure histories to allow correct diagnosis and treatment of these conditions. We report here the epidemiology, clinical appearance, and treatment of tourism-transmitted tropical, ectoparasitic infestations with the sand flea, Tunga penetrans (TP) and the fly, Dermatobia hominis (DH).

Report of Cases

Figure 1	Figure 2

Case 1.—After returning from a trip to Zanzibar, a 26-year-old healthy female noticed one papular, crusted lesion on the first toe of her left foot and another on the fourth toe of her right foot (Fig 1). Examination revealed two firm, crusted, round papules, 0.5 cm in diameter, with well-defined borders, on the distal toes, partly covered by the toenails. Each lesion was curetted in its entirety under local anesthesia. Microscopic examination of the extracted specimen revealed necrotic material and white, oval eggs, compatible with the mature eggs of TP (Fig 2). In addition, parts of an adult flea's body was identified. The eroded areas were covered with mupirocin ointment, and they healed without sequelae.

Case 2.—A 22-year-old healthy man had spent 6 weeks backpacking in Ecuador. One week before his return to Israel, he noted on his right thigh a slightly pruritic skin lesion that resembled an insect bite. It became enlarged and developed into a furuncle-like nodule, which was diagnosed as such by the first examining physician. Examination on admission to our outpatient clinic revealed a raised, inflamed, erythematous, indurated nodule with a central hole from which a white, thread-like structure was seen to move from time to time. The patient described having the sensation of something creeping around at the site. We excised the entire lesion under local anesthesia and found intact larva of DH in the tissue. The incision was sutured and healed with a minimal scar.

Discussion

Tungiasis

Tungiasis is caused by infestation with the female flea Tunga penetrans (TP), also known as sand flea, jigger, nigua, or chigo. The natural habitat of TP is the sandy, warm soil of deserts and beaches and close to farms. Tungiasis is an endemic condition in Central and South America, the Caribbean, the whole sub-Saharan region of Africa (from Sierra Leone, Ivory Coast, Nigeria, and Ethiopia to South Africa, as well as Zanzibar and Madagascar), the Seychelles Islands, Pakistan, and the west coast of India. [1, 2, 3, 4] We are aware of only two reports of tungiasis imported into Israel.[5, 6]

Biologic life cycle.— Reaching a length of only 1 mm, TP is the smallest known flea. Whereas adult fleas need feed only on warm-blooded hosts intermittently, the fertilized females require a host to complete their biologic cycle, they penetrate into the epidermis of a suitable one. The victims can be humans, dogs, cats, rats, pigs, cattle, sheep, and many others. Once the parasite lies within the skin, it thrusts its head into the superficial layers of the dermis, looking for nourishment by puncturing the blood vessels. Its tail is oriented toward the surface, maintaining communication with the outside through a hole in the stratum corneum. This opening provides air for breathing and a passage for both excretions and eggs. The eggs are white and ovoid and number between 100 and 150. Once deposited on the ground, if the environmental conditions are favorable, they enter into a developmental process. They hatch in 3-4 days, liberating larvae that develop within 10-15 days into pupae. After 1-2 weeks, these pupae become adults, thus completing the cycle that takes about 1 month.[1, 2, 3, 4].

Clinical presentation in humans.—The penetration of the flea is asymptomatic; the inflammatory and necrotic phenomena that produce pain and pruritus develop only when the insect increases in size because of egg production. Because this flea is a poor jumper, most lesions occur on the feet (often on the soles, the toe webs, and around or under the toenails), as was seen in our patients. Tungiasis is characterized clinically by a papule or nodule, either single or multiple. The lesions are white, yellow, gray, or black in color, with a brown-black central tip that is the posterior portion of the flea. Erythema may be slight or intense. Lesions are sometimes pustular or ulcerative and, as in our patient, covered by a brownish-black crust. [7, 8, 9, 10, 11]. With the exception of superinfections, mainly caused by Staphylococcus aureus and gram-negative bacteria, and the risk of tetanus, [12] complications of tungiasis are uncommon.

Myiasis Dermatobia hominis (DH)

Myiasis is the infestation of tissues and organs of humans and other animals by the larvae, commonly referred to as maggots, of the order Diptera, two-winged flies or true flies. The infestation is most often subcutaneous and produces a furunculoid or boil-like lesion but can also occur in wounds and certain cavities of the body. Only infestation with the genus DH will be discussed here.

The distribution of DH, the human botfly, ranges from northern Argentina to southern Mexico, and it is usually found in warm, humid, lowland forests [13, 14, 15]. DH is an obligatory parasite whose larval stages can occur only in the living tissue of animal or human hosts. When it affects domestic animals such as cattle, it can produce far-reaching economic problems as well.

Biologic life cycle.—After mating, the female fly seeks out a biting arthropod, such as a mosquito, a tick, or other blood-feeding insect to act as a mechanical vector. The fly is able to capture the insect by holding onto its wings with her legs, whereupon it attaches 15-30 eggs onto the arthropod's abdomen. The fertilized DH female captures a number of such insects in succession for distribution of the 100-400 eggs produced during her 8-9 day life span.

When the biting insect lands on a warm-blooded animal, the increase in surrounding temperature causes the eggs to hatch, and the first-stage larvae are deposited on the skin. The larvae then enter the victim's skin, first by burrowing through the arthropod's skin, and then by entering via the bite of the insect vector, through a hair follicle, or through damaged skin. The recipient is unaware of this penetration, which may take between 5 and 60 minutes.

Figure 3

The larva, which does not migrate from the original site of entry, spends between 4 and 14 weeks in the skin, developing into a third-stage larva (the instar stage), which can measure 2 cm or more in length. It anchors itself in the skin by a number of parallel, concentric rows of posteriorly pointing spines located on its body. Its position is further stabilized by its body shape, which consists of an anterior end wider than its posterior end (Figure 3), a fact that explains why it is difficult to extract a larva without widening the skin opening. The larva then emerges from the skin, again usually without the victim's awareness, and falls to the ground. It then spends between 14 and 30 days in the soil in order to pupate, an become an adult fly. The entire life cycle of the botfly is completed within 3-4 months.

Clinical presentation in humans.—The most common sites where larvae are deposited are exposed areas, such as the upper and lower extremities, the back, and the scalp, although lesions have been reported on the eyelids, tongue, nose, genitalia, buttocks, and brain. Within 24 hours, a small (2-3 mm) erythematous papule resembling an insect bite develops and gradually enlarges to diameter of 10-35 mm and a height of 5-10 mm and is surrounded by a larger area of induration. It usually looks like a large pyogenic furuncle but often has a 2-3 mm breathing hole or punctum at its center where the posterior end of the larva (a small, white, thread-like structure) or movements of fluid or bubbles may be seen. The patient may now feel a sharp pain or stabbing sensation from the outer spines of the larva as it moves.

Conclusions

Global travel has brought with it the introduction of clinical diseases, characteristic of tropical regions, into countries that are not endemic for these conditions. Because "… we see only what we are ready to see, what we have been taught to see. We eliminate and ignore everything that is not a part of our prejudices" [Jean Martin Charcot], we can diagnose only diseases of which we have some knowledge. Therefore, it is of crucial importance that physicians be familiar with tropical diseases. Updated knowledge on the global endemic areas, clinical features, and incubation periods of various diseases, combined with an accurate history of recent travel and a high index of suspicion, are the keys to correct diagnosis.

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