Linear migratory miasis: causes, symptoms, diagnosis, treatment

Linear migratory myiasis is found both in the tropics and in temperate countries, including Russia.

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What causes linear migratory myiasis?

The causative agent of linear migratory myiasis is the larvae of gadflies from the Gastrophilidae family: gastrophilus eque (parasitizes in the stomach and intestines of horses) and, less often , G. intestinalis, G. veterinus, G. haemorhoidalis, G. pecorum.

Symptoms of linear migratory myiasis

Linear migratory myiasis in a temperate climate is most often observed in the summer. Female gadflies lay eggs, attaching them to the hair of a horse or cattle. The larvae that hatch from the eggs continue to develop, burrowing into the skin and causing itching as they parasitize on the skin of animals. When animals lick itchy areas of skin, some of the larvae end up on their tongues and from there in the stomach and intestines. Here, the larvae, having attached themselves to their walls, continue to develop. Having reached their full development in the gastrointestinal tract, the larvae then end up in the environment with the excrement, where they pupate. Humans most often become infected through contact with animals that have first-stage larvae on their fur.

After the larva gets on human skin, thanks to its strong biting organs (chitinous hooks), it drills through the upper layers of the epidermis, penetrates it and then, at the border with the dermis, begins to make long zigzag-shaped passages, sometimes with a bizarre pattern, like tunnels.

At the site of entry of the larva into the skin, an itchy papule-vesicle appears, transforming into a pustule surrounded by an acute inflammatory rim. The larva moves in the skin mainly at night, and during the night it can make a passage from 4-5 to 25-30 cm or more in length. Clinically, on the skin in the area of parasitism of the larva, an uninterrupted narrow (up to 0.5 mm wide), pale pinkish, slightly edematous line is visible, which strictly corresponds to the passage dug by the larva in the skin. By palpation, it is sometimes possible to notice that the line is somewhat raised, and outwardly it can be strikingly similar to the stripes of elevated dermographism.

Often the course of the larva's movement in the epidermis can be determined by the slightly greater juiciness of the inflammatory phenomena in the area of the head end of the emerging line. In other words, the mobile (active) end of the line is somewhat wider, juicier and more intensely colored.

Despite this, attempts to detect the larva at the most clearly visible end of the strip and remove it are usually unsuccessful, since the larva, as a rule, is actually somewhere further away, i.e. in the clinically still non-reactive zone of the skin lesion. In addition, observations of the presence of branching arrangements of passages allowed us to assume that the larva in the process of its movement can return back and continue moving in another direction.

Sometimes, in the head part of the passage, 1-3 cm further from the end of the visible line of movement of the larva, it is possible to palpate a lenticular thickening. Often, a live larva can be extracted with a needle.

Usually the lesion is single, although there are known cases of simultaneous penetration and parasitism of several larvae in the skin. The disease is most often observed in children, as well as in women with delicate skin. Representatives of the white race in tropical conditions get sick somewhat more often than the indigenous population. As the disease develops, the juiciness and brightness of the inflammatory shade gradually subsides in the places of earlier passages, and brownish nuances appear, and sometimes a barely noticeable strip-like peeling is determined.

Linear migratory myiasis usually does not cause any discomfort to patients. Only sometimes, in addition to moderate itching and some burning along the larvae's movement, general symptoms of linear migratory myiasis are observed in the form of moderate fever, nausea, and in children in some cases - agitation, anxiety and even convulsions. The process lasts 1-2 months, rarely longer. Despite such a long period, the larvae of gastric gadflies in human skin still do not undergo full development. They are usually either extracted or die under the influence of certain medicinal agents.

There are known cases of simultaneous infection of several people in industrial conditions, especially at stud farms, which can serve as the basis for diagnosing occupational myiasis with corresponding socio-economic consequences.

Treatment of linear migratory myiasis

Linear migratory myiasis is treated by detecting the larva when examining the skin with a magnifying glass, and especially with side lighting. The suspected location of the larva can also be illuminated with oil (vaseline, peach, etc.). After this, a thin needle or orbital scalpel can be used to try to extract the larva from the epidermis.

Treatment of linear migratory myiasis, in addition to mechanical extraction, involves the use of diathermocoagulation, cryotherapy, freezing with ethyl chloride, and liquid nitrogen.