In people, obligate myiasis is primarily due to the screwworm flies (Old and New World) and the human bot fly. This is termed “obligate myiasis” and is caused by species affecting sheep, cattle, horses and many wild animals. Several fly species must develop in the living tissues of a host. Other muscoid fly species that may be involved in this type of myiasis include: Calliphora vicina, Phormia regina, Cochliomyia macellaria and Sarcophaga haemorrhoidalis. Another calliphorid, Chrysomya rufifacies, has been introduced into the United States from the Australasian region and is also known to be regularly involved in facultative myiasis. In the United States, the blow fly Phaenicia sericata has been reported causing facultative myiasis on several occasions. Numerous species of Muscidae, Calliphoridae and Sarcophagidae have been implicated in facultative myiasis. I once consulted in a case wherein fly maggots were found in a hospital patient’s eye socket. Facultative myiasis may result in considerable pain and tissue damage as fly larvae leave necrotic tissues and invade healthy tissues. Flies in the genera Musca, Muscina, Fannia, Megaselia and Sarcophaga often have been implicated in such cases.įACULTATIVE MYIASIS. Other instances of accidental myiasis occur when fly larvae enter the urinary passages or other body openings. Some notorious offenders are pomace flies and fruit flies (Drosophilia spp.) the cheese skipper, Piophilia casei the black soldier fly, Hermetia illucens and the rat-tailed maggot, Eristalis tenax. Numerous fly species in the families Muscidae, Calliphoridae and Sarcophagidae may produce accidental enteric myiasis. There is some question as to whether or not these cases should be classified as true myiasis because of lack of fly development after the ingested eggs hatch. Accidental enteric myiasis (sometimes referred to as pseudomyiasis) mostly is a benign event, but the larvae possibly could survive temporarily, causing stomach pains, nausea or vomiting. Transmission of myiasis occurs only via an adult female fly.ĪCCIDENTAL MYIASIS. Fly larvae are not capable of reproduction and, therefore, myiasis under normal circumstances should not be considered contagious from person to person.
Obligate myiasis is the most serious form of the condition from a pathogenic standpoint and constitutes true parasitism. Myiasis can also be “obligate,” in which the fly larvae must spend part of their developmental stages in living tissue.
Myiasis can be “accidental,” when fly larvae occasionally find their way into the human body, or “facultative,” when fly larvae enter living tissue opportunistically after feeding on decaying tissue in malodorous wounds. However, pest control personnel should still be concerned about the possibility for myiasis because if it happens in one of your health-care facility accounts, somebody’s going to be sued for not keeping flies out of the facility. Myiasis may be gross and scary, but, generally, it’s not life threatening. Adult flies lay their eggs on or near a neglected or pus-filled wound and developing maggots feed in the affected tissues. When fly larvae get in the tissues of people or animals, the condition is referred to as myiasis.
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