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Myiasis: causes, symptoms, diagnosis, treatment
Last reviewed: 04.07.2025
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Myiasis is an invasion by the larvae of certain species of flies and gadflies; it is characterized by polymorphism of symptoms depending on the localization of the parasite.
ICD-10 codes
- B87. Myiasis.
- B87.0. Cutaneous myiasis.
- B87.1. Wound myiasis.
- B87.2. Ocular myiasis.
- B87.3. Nasopharyngeal myiasis.
- B87.4. Myiasis of the ear.
- B87.8. Myiasis of other localizations. Urogenital myiasis, intestinal myiasis.
- B87.9. Myiasis unspecified.
Epidemiology of myiasis
Larvae of non-parasitic flies cause accidental myiasis. They also develop when eating food products containing fly larvae (intestinal myiasis), when laying eggs on linen that comes into contact with the body, and when larvae penetrate the urethra (urogenital myiasis), conjunctival sac (ocular myiasis), through the ear, mouth, nose (cavitary myiasis).
Facultative myiasis is caused by larvae of non-parasitic species of flies that live in corpses, manure, and rotting plants. The disease occurs when flies lay eggs in wounds, ulcers, nasal passages, and the external auditory canal when there is an inflammatory process in them.
Obligate myiasis is caused by the larvae of parasitic species of flies and gadflies that live in the tissues of humans and warm-blooded animals. The disease occurs when fly larvae (Wolphartian fly) and gadflies penetrate the epidermis or when the gadfly lays eggs in the eyes and nostrils along with the fluid that the female injects in flight.
What causes myiasis?
Myiasis is caused by the larvae of insects of the order Diptera, horseflies and flies. In humans, the most common parasites are the causative agents of obligate myiasis - the larvae of the Wohlfahrtia magnifica fly, gadflies of the Hypoderma and Gastrophilus genera, Cordylobia anthropophaga (the causative agent of cordylobiosis), Dermatobia hominis (the causative agent of dermatobiosis), the sheep gadfly Oestrus ovis and the horse gadfly - Rhinoestrus purpureas. Accidental and facultative myiasis are caused by the larvae of non-parasitic species of flies: the house fly - Musca domestica, the house fly - Muscina stabulans, the small house fly - Fannia canicularis, as well as the blue and green meat and cheese flies.
The larvae are resistant in the environment, can survive in waste water, some are resistant to disinfectants. Flies lay eggs at a temperature of 16-40 °C, the duration of larval development is from 18 days
at 16 °C to 3 days at 36 °C.
Pathogenesis of myiasis
The pathogenesis of myiasis is caused by the localization of the larva, which causes mechanical damage and inflammation, destroying tissue with its enzymes with the development of necrosis, as well as the toxic-allergic effect of metabolites.
Symptoms of myiasis
By localization, there are cutaneous (tissue), cavity, urogenital, eye and intestinal myiasis. Intestinal myiasis is acute, with abdominal pain, vomiting, diarrhea, and fever. The following symptoms of myiasis are characteristic of urogenital myiasis: cutting pain and urinary retention.
In case of wound myiasis, a complicated course in the form of a suppurative process is possible.
In obligate benign myiasis, the larvae (usually gadflies) migrate in the subcutaneous tissue, spreading throughout the body. Itching of the skin is recorded, as well as the appearance of passages made by the migrating larva, which resemble healing scratches. After the larva molts, a capsule forms around it - an infiltrate appears. After a few days, a fistula is formed through which the larvae come out. After this, the infiltrate is absorbed. Severe conditions are possible if the larva perforates the intestinal wall or penetrates the brain. If the larvae enter the eye, conjunctivitis develops, accompanied by cutting pain and lacrimation. The introduction of larvae into the eyeball can lead to blindness. If the larvae parasitize in the nose, a mucopurulent discharge appears from one half of the nose, headache and fever are possible.
In malignant myiasis (causative agent - larvae of the Wohlfahrt fly), the larvae penetrate through damaged skin and mucous membranes into the underlying tissue, causing an inflammatory process in them, causing symptoms of myiasis: intense pain, fever, intoxication, tissue necrosis. If the larva penetrates the brain, a fatal outcome is possible.
Diagnosis of myiasis
Diagnosis of myiasis consists of visual detection of larvae in vomit, wound discharge, etc., depending on the location of the parasite.
What do need to examine?
Differential diagnosis of myiasis
Depending on the localization of the larvae, myiasis is differentiated from food poisoning, salmonellosis and other acute intestinal infections, urethritis, conjunctivitis, rhinitis of other etiologies, phlegmon, and invasion by helminth larvae (Larva Migrans).
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Indications for consultation with other specialists
Consultations with a surgeon, urologist, ophthalmologist or neurologist are recommended, depending on the location of the parasite.
Treatment of myiasis
Treatment of myiasis depends on the form:
- In case of intestinal myiasis - gastric lavage, prescription of a laxative.
- In case of urogenital myiasis - washing the urethra with antiseptics; removal of larvae from the skin of wounds.
- In case of tissue necrosis - surgical treatment of myiasis.
Clinical examination
Dispensary observation of those who have recovered is not indicated.
How to prevent myiasis?
Myiasis can be prevented by improving populated areas and fighting flies (in areas of livestock farming - with gadflies), protecting food products from them. Preventing wounds, skin damage and mucous membranes from flies (gadflies).