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Myiasis
Key Points
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Infestation of vertebrates with dipterous larvae.
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Anatomic (bloodsucking, cutaneous, or cavitary) or ecological (obligatory, facultative, or accidental) classification.
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Cutaneous manifestations include furuncular, migratory, and wound myiasis.
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Dermatobia hominis and Cordylobia anthropophaga are the most common causative agents of furuncular myiasis.
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Clinical features distinguish migratory myiasis from helminthic cutaneous larva migrans.
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Mechanical extraction and surgical removal are the therapies of choice.
Introduction
Myiasis is the infestation of live vertebrates with dipterous larvae. Depending on the body's location, and the relationship of the larvae with the host, the parasite can cause a broad range of medical conditions. Myiasis remains a major economic problem in animal farming, as it leads to reduced milk production, weight and fertility issues, and also reduced hide quality, with consequent economic losses. Human myiasis is found worldwide, but with more species and greater abundance in poor socioeconomic regions of tropical and subtropical countries. In non-endemic countries, myiasis is also an important condition, as it can represent the fourth most common travel-associated skin disease.
Myiasis Classification
There are two main systems for categorizing myiasis:
Anatomic Classification
This classification system is based on the one proposed by Bishop, and later modified by James, and by Zumpt :
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Sanguinivorous or bloodsucking
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Cutaneous: subdivided into furuncular, migratory, and wound infestation myiasis
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Cavitary: subdivided first, according to the organ system affected, into ENT, intestinal, and urogenital myiasis; second, with particular locations, the myiasis may take the name of the affected organ (e.g., cerebral myiasis, aural myiasis, ophthalmomyiasis).
Ecological Classification
This classification is based on the relationship between the fly maggots and the host :
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Specific / obligatory: parasite dependent on host for part of its life cycle
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Semispecific / facultative:
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Primary – normally free living, but may initiate myiasis
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Secondary – normally free living and unable to initiate myiasis, but may be involved once animal is infested by other species
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Tertiary – normally free living and unable to initiate myiasis, but may be involved when host is near death
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Accidental / pseudomyiasis: normally free-living larvae, but cause a pathologic reaction when accidentally in contact with the host.
Taxonomy of the Diptera (True Flies)
To understand fully the ecological classification and the real impact of myiasis, it is necessary to understand the taxonomic classification of the order Diptera, as shown in Figures 31-1 to 31-3 .
Myiasis and Travel Medicine
Increasing international travel, both for tourism and for business, raises physicians' need to make an accurate and timely diagnosis of myiasis. This is important not only to alleviate the patient's symptoms, but also to prevent myiasis-causing flies becoming established in non-endemic regions.
Epidemiology
Poor hygiene is the most important risk factor for acquiring myiasis, with the exception of Dermatobia hominis infestation. Other important risk factors are: geographical location, cultural habits, and open wounds – especially in patients with abundant suppuration, poor vision, mental illness, or other conditions in which the maggot cannot be identified or removed.
Clinical Manifestations
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