Flies that cause myiasis lay their eggs near open wounds or sores. When the maggots hatch, they eat away at the tissue.
Myiasis symptoms include an enlarged bump that looks like a pimple, pain, itching and the sensation of movement. The infection can be severe. It’s important to seek treatment.
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Wound myiasis occurs when fly larvae (maggots) infest open wounds, mucous membranes of the mouth, eyes, and nose, or body cavity openings such as ear canals and sinuses. Flies such as botflies and screwflies can deposit their eggs near a wound or sore that is not being cared for, and the hatched maggots then burrow into the skin. Flies also lay their eggs on objects that can come into contact with a person’s skin, such as damp clothing.
Symptoms vary depending on the type of myiasis. In furuncular myiasis, people have itching and a sensation of movement, as well as sharp, stabbing pain. A bump forms that resembles a pimple, and later enlarges into a pus-like boil with a central pore that drains a serosanguinous fluid.
Other types of myiasis are caused by flies that do not bite. These include cutaneous larval migration (CLM) and migratory oral myiasis, and they are more common in people who live or travel to tropical countries. In these types of myiasis, maggots move away from the site of infection, where they form blister-like lesions that are itchy.
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Symptoms of myiasis depend on the area of the body that is infested. Creeping myiasis occurs when the maggots of flies that can’t develop in humans invade healthy skin, leaving red, inflamed tracks. Itching is a key symptom in these cases.
Wound myiasis is characterized by fly larvae infesting open wounds or ulcers. Tissues that line the mouth, eyes, or other body cavities (mucous membranes) can also become infested. These cases can cause a feeling of movement, itching, and sharp, stabbing pain. Blood tests may show elevated neutrophils and eosinophils.
The New World screwworm (NWS) flies that can cause myiasis feed on live tissue, and infest it with their larvae, which eat the host’s cells. NWS myiasis is most common in areas of South America and the Caribbean. It can affect people who are unsheltered, in poor health, or living in substandard hygienic conditions. These people are at a higher risk of wound myiasis than the general population. It is also a problem among the poor, in psychiatric hospitals, and those who have physical disabilities that prevent them from dissuading flies.
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Infection occurs when the fly larvae burrow into the skin. The infections vary depending on the type of fly and where the infection develops. Wound myiasis involves infestation in open wounds or ulcers; migratory myiasis results from the movement of larvae across the skin, leaving tracks that look like itchy pimples (cutaneous larva migrans); cavitary myiasis is an infection in body cavities, such as the nose and mouth, or intestines; and thromocytic myiasis is an infection of the throat (throat myiasis).
The larvae of some species of flies, including green or black blowflies, are attracted to open wounds and infest them. They also move into healthy tissue and may invade the tissues that line the nose, eyes, and ears (mucosa). These flies commonly infest people who live or travel in tropical countries.
The resulting infected lesion appears as a pus-filled bump, called a furuncle, on the skin, usually in areas that are exposed to the sun, such as the lower legs or arms, head, and neck. A patient experiences pain, itching, and a sensation of crawling in the skin.
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Myiasis is caused by the maggots of certain fly species, which are parasites that feed on and penetrate healthy tissue. It usually occurs in people who have a wound that is not covered or cleaned and who are living or traveling in a tropical region.
Myiases are not contagious from person to person. However, it is possible to contract a myiasis-causing infection by eating something with fly eggs on it. If you have a food-borne myiasis, it may be treated with anti-parasitic medications such as oral ivermectin.
Myiasis of the skin, or furuncular myiasis, involves flies whose eggs can breach healthy skin, such as botfly (Cordylobia anthropophaga), screw worm fly (Diptera hominis), and human tumbu fly (Cordylobia rodhaini). It appears on bare skin in the form of an oozing, red bump that resembles a boil or pimple (furuncle). As it grows, the larva develops a central pore through which fluid drains, and itching and a sensation of movement occur. It takes around 15 days for the lesion to enlarge to a pus-filled or purulent cyst or pseudofuruncle.
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The infestation of cutaneous tissues by the larvae of the order Diptera may be deleterious as in furuncular myiasis or beneficial, as when the maggots confine their activities to diseased and dead tissue in wound myiasis. A complication is secondary bacterial infection as reported in some cases. Intestinal myiasis may cause abdominal pain, vomiting and diarrhea and urogenital myiasis may cause hematuria. Cerebral myiasis is associated with reduced mental status, motor deficits and extrapyramidal symptoms.
Infections with the flies of the order Diptera rarely cause permanent harm to humans. Myiasis is most often caused by noninvasive blowflies that lay eggs in preexisting wounds. Infections with the flies of this order are most often seen in poor countries and may reflect patient neglect in hospitals where medical care is limited. Nosocomial myiasis occurs in patients with wound infections or in patients who require assisted breathing or tracheotomies. Wound myiasis is most often associated with skin malignancies such as basal cell carcinoma and squamous cell carcinoma, but it has also been reported in patients with angiosarcoma, melanoblastoma and larynx cancer.