Deep skin myiasis: causes, symptoms, diagnosis, treatment

The group of deep myiasis (myasis cutis profunda) includes diseases that differ in etiology and clinical course, the unifying factor of which is the deep penetration of larvae into the dermis, subcutaneous fat and underlying tissues. Deep myiasis of the skin is characterized by malignancy. Among them are common deep myiasis, African myiasis, or cordylobiosis, and South American myiasis, or dermatobiosis.

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Deep myiasis of the skin

Common deep myiasis of the skin (myasis vulgaris profunda) as a type of deep myiasis, in addition to hot countries, is sometimes observed in countries with a temperate climate, including Russia, where myiasis of the eyes (ophthalmomyiasis), myiasis with damage to the organ of hearing, myiasis of the nose, tongue, and urethra have been described.

The causative agents of common deep myiasis can be the larvae of the following flies: Wohlfortia magnifica, W. veigil, W. intermedia (North America, southern Europe, a number of Middle Eastern countries, Egypt, China, Mongolia), Chrisomyia hominivorax, Ch. macellarica, Ch. bezziana, Vilinemee, etc. (East Africa, some Asian countries).

In ordinary deep myiasis, female flies usually lay eggs, most often in the foci of various skin lesions (suppurating abrasions, wounds, ulcers, etc.). The larvae formed from the eggs, unlike superficial myiasis, feed not only on necrotic tissues, but also on healthy tissues. Upon careful examination (especially with a magnifying glass), at this stage, one can notice a peculiar movement of larvae in the wound, which are located under the overhanging edges of ulcers or folds as if in whole colonies. They, corrode the tissues, not only cause their destruction, but can even be the cause of the development of deep defects. In such cases, the patient usually experiences general symptoms of deep skin myiasis in the form of fever, headaches, weakness, almost constant acute pain; even fainting is possible.

In addition to the skin, the larvae can also be found on the mucous membrane of the mouth, nose, and eyes, where, devouring the mucous membranes, they make deep passages in the tissues, right down to the fascia and even the periosteum, which leads to extensive and severe destruction of not only soft tissue, but even cartilaginous and bone tissue of the larynx, nasopharynx, paranasal sinuses, eye sockets, middle ear, etc. There are even known cases of complete destruction of the eyeball with the development of encephalitis and death.

Although the period of parasitism of Wohlfahrt fly larvae on humans usually does not exceed 3-6 days, after which they fall off the skin and pupate outside the body, this is quite enough to cause deep destruction. It is possible that in some cases, apparently, repeated laying of new and new portions of eggs takes place. Moreover, it is known that sometimes foci of ordinary deep myiasis can become "mixed" as a result of the deposition of new larvae by other types of flies.

Treatment of deep skin myiasis

First of all, it is important to remove all larvae from the affected areas as soon as possible. In most cases, washing the area with any disinfectant solution (1% chloroform water, 2% resorcinol solution, potassium permanganate solution, etc.) is sufficient. Antibiotics and sulfonamides are used as indicated, and in cases of deep purulent processes, surgical intervention is used.

African myiasis

African myiasis (myasis africana), or furunculoid myiasis (synonym: cordilobiasis ) is especially common on the African continent.

The causative agent is the larva of the fly Cordilobia anthropophaga. The infection route may be as follows: the female fly lays a large number of eggs on soil surfaces contaminated with urine and organic waste. The tiny larvae hatch from them, when in contact with human skin, as well as some mammals, in particular dogs, rats, etc., actively penetrate (burrow) into the thickness of the skin.

Most often, African myiasis affects children as a result of playing with the soil, as well as adults who have contact with the soil, especially in industrial conditions (workers in rice, coffee, rubber plantations, etc.). After 1-2 days, a hyperemic focus appears at the site of the larvae's introduction into the skin, at the base of which a nodular infiltrate can be palpated. As the infiltrate increases, a furuncle-like node forms in the next few days, which has a small hole in the center for air access to the larva. The clinical symptoms of African myiasis fundamentally distinguish furunculoid myiasis from a staphylococcal furuncle with its necrotic core in the center.

On the 12th-15th day from the onset of the disease, the larva begins to protrude from the increasing opening leading into the cavity of the node as it grows. At this stage, it can be up to 10-15 mm long. If the outcome is favorable, it soon leaves the skin, falling out into the external environment and pupating in the soil, after which the wound heals. Furunculoid myiasis often occurs as a single lesion, but there are numerous known cases of multiple penetration of larvae into the skin of one person with the formation of several furuncle-like infiltrates.

Some patients may experience infection and suppuration of the wound with the formation of a large abscess. This development is especially facilitated by the rupture of the larva during an inept attempt to extract it, as well as contamination of the wound.

Treatment of African myiasis

Before the larva matures, any treatment, especially mechanical extrusion, is inappropriate and can only lead to secondary infection. Treatment of African myiasis begins with a mature larva and an enlarged ventilation duct opening and consists of careful mechanical removal of the larva by stretching the skin around the lesion. In order to speed up the exit of the larva, you can fill the funnel-shaped opening of the opened node with some sterile oil (camphor, petroleum jelly, peach, etc.), while the larva, deprived of access to air, approaches the surface of the skin and begins to stick out its usually rear end of the body with a breathing apparatus. At this point, it can be easily removed with tweezers.

After the larva is removed, the freed cavity is washed with any disinfectant solution and an antiseptic bandage is applied. In case of complications with secondary infection, external or systemic antibiotics may be indicated.

Deep myiasis of the skin can be prevented. Preventive measures of control are mainly reduced to early detection and timely rational treatment of all skin lesions, as well as preventing access of flies to them; for this purpose, the use of repellents is recommended. Also of great importance is the destruction of flies, the fight against myiasis of animals, especially rats and dogs.

South American myiasis

South American myiasis (myasis Sudamericana) is a type of deep myiasis (synonym: dermatobiasis ) found mainly in some subtropical countries of Latin America. It is caused by the larva of the human gadfly - Dermatobia hominis. Unlike the African myiasis described above, with this type the female gadfly does not lay eggs in the soil, but rather glues them to the body of blood-sucking dipterous insects (mosquitoes, horseflies, stinging flies and even houseflies) and some types of ticks, where the larvae mature. Then, when these insects attack human skin (as well as domestic ungulates, monkeys, jaguars, tigers, birds, etc.), the larvae released from the eggs quickly and very actively penetrate it.

The further course of the disease is characterized by the formation of an inflammatory infiltrate at the site of the larval introduction after a few days, and then a subcutaneous node, which in turn turns into an abscess. It opens with the release of a small amount of serous-purulent fluid and the formation of a fistulous tract, which is necessary for the larva to access air. In the cavity of the abscess, the larva continues to develop and after 1-2.5 months, having fully matured (reaching a length of 20-25 mm), leaves the human body and pupates in the soil.

The symptoms of South American myiasis are usually minor and consist mainly of a moderate feeling of pain, especially in the adult larval stage.

The prognosis is generally good, although a rare case of death of a city child infected with multiple larvae has been described.