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ABSTRACT |
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Myiasis is defined as infestation of a vertebrate host by fly larvae that feed on living tissue, body fluids, or ingested foods. Furuncular myiasis is caused by Dermatobia hominis, the human botfly or Cordylobia anthropophaga, the African tumbu fly, which produce boil-like lesions commonly misdiagnosed as a furuncle.1 Dermatobia hominis is endemic through much of Central and South America. Its larvae are transmitted to vertebrate animals by hematophagous insects, most commonly mosquitoes, on whose abdomens the female botfly has deposited her eggs. When the blood-feeding vector encounters a warm-blooded animal, the change in temperature causes the botfly eggs to hatch. The larvae enter the vertebrate host either through a hair follicle, the bite site, or by directly burrowing in the skin. Over the next 4–18 weeks, the larva grows by eating the flesh of its host. At maturity it emerges from the wound, falls to the soil, and pupates. Despite its name, D. hominis also infests domestic livestock such as cattle and wild animals such as monkeys, rodents, and birds.2 Because the botfly is not endemic in the United States and the lesion it makes resembles a furuncle, the diagnosis is often missed in returning travelers.
A 19-year-old man came to the student health clinic at the University of Miami (Coral Gables, FL). Three weeks earlier, he had returned from a trip to the Costa Rican rain forest with his tropical field biology class. In Costa Rica, the student had spent one week backpacking from a cloud forest approximately 2,900 meters above sea level to a lowland rain forest 30 meters above sea level where he was exposed to mosquitoes and tabanid flies, all of which can carry botfly eggs. Upon returning from the trip, he reported that one mosquito bite on his left lower leg did not heal and instead enlarged. The patient noted an intermittent serosanguinous discharge and a painful but brief biting sensation that occurred an average of two times per day. The patient denied fever, vomiting, headaches, and other constitutional symptoms.
On examination, the patient had a 1.3-cm erythematous nodule with a central pore on the lateral aspect of the lower left leg. The patient did not have regional lymphadenopathy or fever. The nurse practitioner who saw the patient diagnosed an infected mosquito bite and prescribed a warm salt-water dressing and a course of cephalexin. The patient completed the prescribed treatment without improvement. He then saw his private physician who performed magnetic resonance imaging (MRI) of the left lower leg, which is shown in Figure 1
. The MRI showed a subcutaneous segmented nodule; however, its morphology did not aid in the diagnosis. Although the physician did not diagnose D. hominis, he suspected a tropical parasite and had the patient return to his tropical field biology professor who was familiar with parasites native to Costa Rica. The professor diagnosed D. hominis and instructed the patient to apply several layers of nail polish to the area so that it covered the central pore and extended at least 1.0 cm to each side of the pore. The nail polish was left on overnight and the next day it was removed with a single swift motion. The protruding larva was grasped immediately with forceps and completely extracted with gentle, continuous tension together with manual pressure exerted on the sides of the nodule. The patient recovered completely with an uncomplicated course.
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We do not advocate the use of the MRI in cases of furuncular myiasis because as we show here, it does not aid in the diagnosis. Moreover, the cost of a lower extremity MRI as reimbursed by insurers exceeds $800, a cost that is avoidable for an infestation that can be diagnosed on clinical grounds. This case illustrates how lack of awareness of tropical diseases can lead to inappropriate and unnecessary diagnostic tests. Some physicians have found, however, that Doppler ultrasound can aid in the diagnosis of furuncular myiasis and is especially helpful in ensuring that all larvae are extracted from a multiply-infected lesion, a situation that is observed infrequently.8
Furuncular myiasis should be considered in a patient who has traveled recently to a botfly-endemic area and who has a furuncular lesion. The furuncle has a central pore that intermittently exudes a serosanguinous discharge (the feces of the larva), and protrusion of the breathing tube of the larva frequently can be observed with the aid of a hand lens. Although characteristic lesions are occasionally accompanied by enlargement of the draining lymph node, there are no other systemic symptoms. The lesions are not responsive to antibiotics. Because ecotourism to Central and South America and immigration to the United States from parasite-endemic countries has become increasingly common, the incidence of D. hominis infection within the United States is likely to increase.
Received October 12, 2006. Accepted for publication November 25, 2006.
Financial support: Photini Sinnis is supported by a grant from the National Institutes of Health (R01 AI056840).
Disclosure: The authors declare that they have no competing interests.
* Address correspondence to Photini Sinnis, Department of Medical Parasitology, New York University School of Medicine, 341 East 25th Street, New York, NY. E-mail: photini.sinnis{at}med.nyu.edu 
Authors’ addresses: Ramanth Bhandari and Photini Sinnis, Department of Medical Parasitology, New York University School of Medicine, 341 East 25th Street New York, NY 10010, Telephone: 212-263-6818, Fax: 212-263-8116. E-mails: ramanath.bhandari{at}med.nyu.edu and photini.sinnis{at}med.nyu.edu. David P. Janos, Department of Biology, University of Miami, PO Box 249118, Coral Gables, FL 33124, Telephone: 305-284-6300, E-mail: davidjanos{at}miami.edu.
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