Introduction
Background
Myiasis is an infestation of the skin by developing larvae (maggots) of a variety of fly species (myia is Greek for fly) within the arthropod order Diptera . Worldwide, the most common flies that cause the human infestation are Dermatobia hominis (human botfly) and Cordylobia anthropophaga (tumbu fly).
In cutaneous myiasis, the 2 main clinical types are wound myiasis and furuncular (follicular) myiasis.1 In nasopharyngeal myiasis, the nose, sinuses, and pharynx are involved. Ophthalmomyiasis affects the eyes, orbits, and periorbital tissue, and intestinal and urogenital myiasis involves invasion of the alimentary tract or urogenital system.2
A rare type of myiasis, hematophagous myiasis, is common in infants younger than 9 months, especially in those living in rural and endemic areas, and the furuncular lesions are usually on the face.3
Pathophysiology
The pathophysiology of the human infection differs depending on the type of fly.
Dermatobia hominis (human botfly) - Endemic to tropical Mexico, South America, Central America, Trinidad
The adult fly resembles a bumblebee; it is short lived and survives for little more than a week. It does not feed and is infrequently seen. The life cycle of the botfly is unique, as the female, egg-bearing fly attaches her eggs to the abdomen of a blood-sucking arthropod (means of transportation known as phoresy), usually a mosquito (although 40 other species of insects and ticks have been reported). When the mosquito takes a blood meal from a warm-blooded animal, the local heat induces the eggs to hatch and drop to the skin of the host and enter painlessly through the bite of the carrier or some other small trauma.
Once deposited in the skin, the larvae start out as small and fusiform and later become pyriform to ovoid as they reach full development at lengths of 15-20 mm. They are encircled by several rings of spines. Eventually, if the cycle is unperturbed, larvae emerge from the host in 6-7 weeks and drop to the ground, where they pupate to form flies in 2-3 weeks.
Cordylobia anthropophaga (tumbu fly) - Endemic to sub-Saharan Africa
The adult fly is about the size of a housefly but stockier. It prefers shade and is most active in the early morning and afternoon. It is attracted by the odor of urine and feces. The females lay their eggs on dry, sandy soil or on clothing. The eggs hatch in 1-3 days and can survive near the soil surface or on clothes for up to 2 weeks waiting for contact with a suitable host. Activated by heat, such as the body heat of the potential host, they are capable of penetrating the unbroken skin. They become fusiform to ovoid and reach a length of 13-15 mm. Their larval stage is shorter than that of the human botfly and is completed in 9-14 days.
Hypoderma bovis/Gasterophilus intestinalis - Creeping/migratory myiasis
The adult fly of the Hypoderma genus is large and hairy and resembles a bumblebee. Normal hosts for the larvae of this fly are deer, cattle, and horses. Humans are abnormal hosts, in which the parasite is unable to complete its development. Human infections usually occur in the rural areas where cattle and horses are raised. In animals, the fly attaches the eggs to the hairs. The larvae hatch, penetrate the skin, and wander extensively through the subcutaneous tissues, eventually locating under the skin of the back, where they produce the furuncular lesions. In humans, the larvae migrate rapidly (as much as 1 cm/h) and erratically through the subcutaneous tissues, producing intermittent, painful swelling over months. The larvae may emerge spontaneously from the furuncles or die within the tissues. In the rare case, the larvae are seen invading the orbit, pharyngeal region, and spinal canal.
The larvae of the Gasterophilus genus are usually gastrointestinal or nasal parasites of horses. In humans, the young larvae burrow in the skin creating narrow, tortuous, erythematous, and linear lesions with intense pruritus. Lesions usually advance 1.5 cm/d. Death of the larvae terminates the infection in 1-2 weeks without sequelae.
Cochliomyia americana/Chrysomyia bezziana - Wound myiasis
The adult flies are rather stocky flies and metallic blue-green to purplish black in color. The larvae are pinkish, fusiform, and strongly segmented. Female flies deposit the eggs near any breaks in the skin or around the nose, mouth, or ears if a discharge is present. Flies may be dispersed by prevailing winds, and infection is often acquired while resting outside during the day or may result from trauma.3,4Frequency
United States
Myiasis is uncommon in the United States, and any cases reported are usually imported cases of myiasis from travelers returning from tropical destinations. However, reported incidence rates are increasing among individuals from nonendemic countries who have traveled to tropical destinations or engage in outdoor activities.5 A study in urban and suburban United States found an association of homelessness, alcoholism, and peripheral vascular disease with cutaneous myiasis; the most common fly identified in that study was Phaenicia sericata (green blowfly).1International
Myiasis is a worldwide infestation with seasonal variation, the prevalence of which is related to the latitude and life cycle of the various species of flies. Its incidence is higher in the tropics and subtropics of Africa and the Americas. The flies responsible prefer a warm and humid environment and so are restricted to the summer months in the temperate zones, while living year-round in the tropics.1 Dermatobia hominis, also known as human or tropical botfly, is endemic to tropical Mexico, South America, Central America, and Trinidad,4 while Cordylobia anthropophaga (tumbu fly) is endemic to sub-Saharan Africa.
Mortality/Morbidity
Myiasis is a self-limiting infestation with minimal morbidity in the vast majority of cases.1
Cases of neonatal fatal cerebral myiasis, caused by the penetration of larva through the fibrous portion of the fontanel, have been reported.5
Race
Myiasis is not prevalent in any particular race.
Sex
No sex predilection exists for myiasis.
Age
Myiasis may occur at any age.
Clinical
History
- Often, a history of traveling to a tropical country or existence of a previous wound is noted.
- Patients complain of boil-like lesions usually on exposed areas of the body, like the scalp, face, forearms, and legs.
- Lesions can be painful, pruritic, and tender, and patients often have the sense of something moving under the skin. Sometimes, patients also complain of fever, swollen glands, or extremities.
- In the cases of ophthalmomyiasis, patients complain of severe eye irritation, redness, foreign body sensation, pain, lacrimation, and swelling of the eyelids.6
- In the cases of nasal myiasis, patients present with epistaxis, foul smell, passage of worms, facial pain, nasal obstruction, nasal discharge, headache, dysphagia, and sensation of foreign body in the nose.7,8
Physical
- Furuncular myiasis : This type of myiasis , caused by both the human botfly and the tumbu fly, causes boil-like lesions. Whereas myiasis from the tumbu fly occurs on the trunk, thigh, and buttocks, botfly lesions are on the exposed areas of the body, including the scalp, face, forearms, and legs. A pruritic erythematous papule develops within 24 hours of penetration, enlarging to 1-3 cm in diameter and almost 1 cm in height. These lesions can be painful and tender. Each has a central punctum from which serosanguineous fluid may be discharged. Lesions may become purulent and crusted; the movement of the larva may be noticed by the patient.1 The tip of the larva may protrude from the central opening (punctum), or bubbles produced by its respiration may be seen.3 The inflammatory reaction around the lesions may be accompanied by lymphangitis and regional lymphadenopathy.2
- Wound myiasis: In wound myiasis , the larvae are deposited in a suppurating wound or on decomposing flesh. The diagnosis is obvious when larvae are visible on the surface of the wound and more difficult when they have burrowed beneath the surface.1
- Creeping cutaneous myiasis: Creeping (or migratory) cutaneous myiasis may be caused when there is exposure to infested cattle or in those who work with horses. This form of myiasis resembles cutaneous larva migrans, with an apparent tortuous, thread-like red line that ends in a terminal vesicle marking the passage of the larva through the skin. The larva lies ahead of the vesicle in apparently normal skin.2
- Ophthalmomyiasis externa: Ophthalmomyiasis externa, caused by Oestrus ovis, is characterized by conjunctivitis, lid edema, and superficial punctate keratopathy in response to movement of larvae across the external surface of the globe. Larvae may appear within the cornea, lens, anterior chamber, or vitreous body but rarely undergo development once the globe has been entered.4
- Nasal myiasis: In nasal myiasis, examination of the nose (rhinoscopy) reveals an edematous, ulcerated mucous membrane filled with necrotic material and crawling maggots. Patients may have septal perforation or palatal perforation or both. Erosion of the bridge of the nose and adjacent area of the face can also be seen as well as orbital cellulitis and diffuse cellulitis of the face. In a smaller number of patients, examination reveals extensive ulceration of the tonsils and the posterior pharyngeal wall due to maggots.8
Causes
As mentioned above, the cause for myiasis is the infestation of humans with the larvae of the Diptera order of fly species. More than a hundred species of Diptera have been reported to cause human myiasis. Some of the most important are as follows:
- Dermatobia hominis (human botfly) causes furuncular myiasis.
- Cordylobia anthropophaga also causes furuncular myiasis.
- Cochliomyia hominivorax (America) and Chrysomyia bezziana (Africa, Australia, Asia) both cause wound myiasis.
- Hypoderma bovis (infested cattle) and Gasterophilus intestinalis (infested horses) both cause creeping (migratory) myiasis.
- Oestrus ovis (sheep botfly) causes ophthalmomyiasis.
More on Myiasis |
 Overview: Myiasis |
| Differential Diagnoses & Workup: Myiasis |
| Treatment & Medication: Myiasis |
| Follow-up: Myiasis |
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| References |
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References
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Burns T, Breathnach S, Cox N, Griffiths C. Diseases caused by arthropods and other noxious animals. In: Rook's Textbook of Dermatology. Vol 2. 7th ed. Malden, MA: Blackwell Publishing; 2004:33.8 - 11.
Auerbach PS. Arthropod envenomation and parasitism. In: Wilderness Medicine. 5th ed. Philadelphia, PA: Mosby Elsevier; 2007:969-974.
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Cestari TF, Pessato S, Ramos-e-Silva M. Tungiasis and myiasis. Clin Dermatol. Mar-Apr 2007;25(2):158-64. [Medline].
Masoodi M, Hosseini K. External ophthalmomyiasis caused by sheepbotfly (Oestrus Ovis) larva: a report of 8 cases. Arch Iran Med. 2004;7:136-139.
Aydin E, Uysal S, Akkuzu B, et al. Nasal myiasis by fruit fly larvae: a case report. Eur Arch Otorhinolaryngol. Dec 2006;263(12):1142-3. [Medline].
Sharma H, Dayal D, Agrawal SP. Nasal myiasis: review of 10 years experience. J Laryngol Otol. May 1989;103(5):489-91. [Medline].
Garvin KW, Singh V. Case report: cutaneous myiasis caused by Dermatobia hominis, the human botfly. Travel Med Infect Dis. May 2007;5(3):199-201. [Medline].
Ofordeme KG, Papa L, Brennan DF. Botfly myiasis: a case report. CJEM. Sep 2007;9(5):380-2. [Medline].
Quintanilla-Cedillo MR, Leon-Urena H, Contreras-Ruiz J, Arenas R. The value of Doppler ultrasound in diagnosis in 25 cases of furunculoid myiasis. Int J Dermatol. Jan 2005;44(1):34-7. [Medline].
Lebwohl MG, Heymann WR, Berth-Jones J, Coulson I. Myiasis. In: Treatment of Skin Diseases. Comprehensive Therapeutic Strategies. 2nd ed. Elesevier-Mosby; 2006:420-421.
Osorio J, Moncada L, Molano A, et al. Role of ivermectin in the treatment of severe orbital myiasis due to Cochliomyia hominivorax. Clin Infect Dis. Sep 15 2006;43(6):e57-9. [Medline].
Costa DC, Pierre-Filho Pde T, Medina FM, Mota RG, Carrera CR. Use of oral ivermectin in a patient with destructive rhino-orbital myiasis. Eye. Sep 2005;19(9):1018-20. [Medline].
Clyti E, Nacher M, Merrien L, et al. Myiasis owing to Dermatobia hominis in a HIV-infected subject: Treatment by topical ivermectin. Int J Dermatol. Jan 2007;46(1):52-4. [Medline].
Further Reading
Keywords
myiasis, blow fly, botfly, human myiasis, myiasis treatment, maggots, infestation of maggots, Dermatobia hominis, human botfly, Cordylobia anthropophaga, tumbu fly, cutaneous myiasis, furuncular myiasis, wound myiasis, ophthalmomyiasis, suffocation techniques, ivermectin
