DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/myiasis/.
[Cochliomyia hominovorax] [Dermatobia hominis] [Cuterebra spp.] [Oestrus ovis] [Cordylobia anthropophaga] [Phaenicia spp.] [Phormia regina]
Myiasis is infection with the larval stage (maggots) of various flies. Flies in several genera may cause myiasis in humans. Dermatobia hominis is the primary human bot fly. Cochliomyia hominovorax is the primary screwworm fly in the New World and Chrysomya bezziana is the Old World screwworm. Cordylobia anthropophaga is known as the tumbu fly. Flies in the genera Cuterebra, Oestrus and Wohlfahrtia are animal parasites that also occasionally infect humans.
Adults of Dermatobia hominis are free-living flies . Adults capture blood-sucking arthropods (such as mosquitoes) and lay eggs on their bodies, using a glue-like substance for adherence . Bot fly larvae develop within the eggs, but remain on the vector until it takes a blood meal from a mammalian or avian host. Newly-emerged bot fly larvae then penetrate the host's tissue . The larvae feed in a subdermal cavity for 5-10 weeks, breathing through a hole in the host's skin. Mature larvae drop to the ground and pupate in the environment. Larvae tend to leave their host during the night and early morning, probably to avoid desiccation. After approximately one month, the adults emerge to mate and repeat the cycle. Other genera of myiasis-causing flies (including Cochliomyia, Cuterebra, and Wohlfahrtia) have a more direct life cycle, where the adult flies lay their eggs directly in, or in the vicinity of, wounds on the host . In Cochliomyia and Wohlfahrtia infestations, larvae feed in the host for about a week, and may migrate from the subdermis to other tissues in the body, often causing extreme damage in the process.
Dermatobia hominis and C. hominovorax are Neotropical species, ranging from Mexico into South America. The Congo floor maggot (Auchmeromyia luteola) and Cordylobia anthropophaga are distributed in Africa south of the Sahara. Wohlfahrtia magnifica occurs in the Mediterranean basin, Near East, and Central and Eastern Europe; W. vigil occurs in northern United States and Canada. Cuterebra species are found in the New World. Oestrus ovis is found throughout the world in areas where sheep are tended.
Infestations with D. hominis are often characterized by cutaneous swellings on the body or scalp that may produce discharges and be painful. Death is rare, but there have been instances of cerebral myiasis in children where larvae enter the brain. Infestations with C. hominovorax, which causes wound myiasis, can be more serious, as this species may travel through living tissue in the body and not stay subdermal like most of the other species of flies that cause myiasis. Death has occurred with severe infestations of C. hominovorax. Secondary bacterial infections may also occur. Oestrus ovis has been known to cause a condition called ophthalmomyiasis, which is infection of the eye with fly larvae. Flies in the genera Phormia and Phaenicia cause facultative myiasis, where adult flies lay their eggs in pre-existing, festering wounds and do not invade healthy, living tissue.