Myiasis is the invasion of organs and tissues of humans or other vertebrate animals by fly larvae, which at least for some time feed upon the living or dead tissues or, in the case of intestinal myiasis, on the host's ingested food.

Types of myiasis

Myiasis may be accidental, obligatory or facultative.

Accidental myiasis usually involves eating food that is contaminated by eggs or larvae of flies that are not parasitic in mammals, such as house-flies. Although the larvae may survive for some time in the intestine, no flies are specially adapted to cause intestinal myiasis in humans. (In contrast, obligatory intestinal myiasis occurs in animals.) The presence of larvae in the human intestine may nevertheless cause considerable discomfort, abdominal pain and diarrhoea, which may be accompanied by discharge of blood and vomiting. Living larvae may be passed in excreta or vomit.

In obligatory myiasis it is essential for the fly maggots (larvae) to live on a live host for at least a part of their life. For example, larvae of Cordylobia anthropophaga, Cochliomyia hominivorax, Chrysomya bezziana, Dermatobia hominis and Wohlfahrtia magnifica are obligatory parasites of humans and other vertebrates.

In contrast, in facultative myiasis larvae are normally free-living, often attacking carcasses, but under certain conditions may infect living hosts. Several types of fly, including species of Calliphora, Lucilia (= Phaenicia), Phormia and Sarcophaga, which normally breed in meat or carrion, may cause facultative cutaneous myiasis in people by infecting festering sores and wounds.