Cutaneous Myiasis: Diagnosis, Treatment, and Prevention

Abstract

Myiasis, from the Greek myia for “fly,” has been defined as the infestation of live human or vertebrate animals with larvae of the insect order Diptera (flies), which feed on living or necrotic tissue. The majority of flies causing myiasis can be categorized into 1 of 2 groups, based on relationship with their hosts. Obligate parasites grow only on healthy tissue of live hosts whereas facultative parasites, associated usually with carrion, feces, or decaying plant material, can develop on necrotic tissue of living animals and tend not to invade healthy tissue. Accidental infestations represent a third category in which the eggs or larvae of saprophagous flies are inhaled or swallowed inadvertently with contaminated food (gastrointestinal myiasis). Myiasis can also be classified according to the site of infestation. Cutaneous myiasis involves the invasion of the skin, with the most common target being a wound, near which an obligatory or facultative parasitic fly will lay eggs. In “wound myiasis,” both healthy and necrotic tissues can be fed on by the larvae, depending on the conditions and species of fly involved. Other flies (eg, the human botfly Dermatobia hominis [L. Jr.] in tropical America, the “tumbu fly” Cordylobia anthropophaga [Blanchard and Berenger-Feraud] in tropical Africa, and Wohlfahrtia vigil [Walker] in North America) penetrate healthy skin and produce itchy sores that develop into painful boil-like lesions or furuncles, hence the term “furuncular myiasis.” Creeping myiasis is a type of cutaneous myiasis involving the migration of fly larvae underneath the skin. Apart from the skin, the eyes, ears, nose, and sinuses represent relatively common sites of attack whereas less common sites are the mouth, throat, urogenital, and gastrointestinal tracts. The invasion of body orifices is sometimes considered accidental myiasis, especially when the larvae cannot complete their development. The most severe cases of myiasis involve obligate parasites, typically those invading wounds or mucous membranes associated with body orifices (screwworm flies) in tropical America (Cochliomyia hominivorax Coquerel) or in the Old World (Chrysomya bezziana Villeneuve, Wohlfahrtia magnifica Schiner), although some facultative myiasis can be dangerous if left untreated. Myiasis occurs mainly in tropical and subtropical latitudes and often originates in these areas even when reported in temperate climates. The main contributing factors are probably the higher levels of exposure to myiasis-causing flies due to poorer clothing and hygiene conditions, combined with the increased aggressiveness of myiasis-causing flies in the tropics. Nevertheless, many cases acquired in temperate parts of Eurasia and North America, including Canada, have been described in the literature. Despite these records, human myiasis remains an unfamiliar illness for most physicians in North America; misdiagnosis and inappropriate treatment are common. Awareness of myiasis by health professionals *Doctoral Student, Laboratoire d’Organogenese Experimentale