Myiasis (myiasis)

MYIASIS, myiasis (from Greek myia - fly, other transcriptions: myiosis, myasis), a disease of man and animals caused by fly larvae. In some species of flies

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Figure 1. "Rat-tailed maggot". Figures 2 and 3. Cordylobia anthropophaga: from the back (2) and from the belly (3). Figure 4. Musca domestica, larva. larvae are obligate parasites, in others saprophytes, and in still others they live by consuming fresh plant matter. All these biological forms of larvae can be true or false parasites of man and animals and cause their host often very substantial, and sometimes irreparable damage. Fly larvae are relatively resistant to various factors, in particular chemical reagents. One can note the ability of the "rat-tailed maggot" - the larva of the fly Eristalis (Fig. 1) - to inhabit sewage and other highly contaminated places (accumulations of liquid feces, etc.); the larvae of many flies do not die for a long time compared to the larvae of other insects in formalin or alcohol solutions. All these features of fly larvae determine their ability to live for a certain period in an unusual environment for them, e.g., in the human intestine, where they can get with food. Myiasis is a general term defining the presence of living fly larvae in a living host. Forms of myiasis are classified both by the location of the larvae in the host and by the biological properties of the larvae of the corresponding fly species. Myiasis can be obligate or facultative with respect to a given species; in the first case, it is caused by parasitic flies, in the second - by flies whose larvae are not parasites. Among flies of the latter category, the larvae of some live in corpses or meat, and their parasitization in a living organism is easily accomplished. The larvae of other species are saprophytic or herbivorous; however, they can also be accidental causes of myiasis. According to localization, cutaneous, tissue, cavity (ear, nose), intestinal, urinary tract, genital, and ocular myiasis are distinguished. - I. Cutaneous (t i s s u e) myiasis in turn occurs in various forms. 1) Epidermal myiasis; larvae live in the thickness of the epidermis and do not go beyond its limits (e.g., the larva of the 1st phase of the gadfly Gastrophilus, causing creeping disease). 2) Subcutaneous myiasis with localization of larvae in the connective tissue layers of the skin, and the epidermis may also be affected secondarily (e.g., the cattle warble fly Hypoderma, the larvae of which can also temporarily parasitize humans); the corresponding form of myiasis has been named subcutaneous myiasis with a migrating skin swelling over the migrating larva; the larvae of the human botfly Dermatobia and the fly Cordylobia anthropophaga (Figs. 2 and 3) cause the development of furuncular myiasis. 3) Subcutaneous myiasis can pass into tissue myiasis when the larvae of myiasis get into ulcers or wounds and begin to devour the living tissue of the host's body; ultimately, enormous destruction of the soft parts of the body can occur (see separate table, figures 2 and 3) with exposure of bones (figure 5); such forms of myiasis sometimes take a generalized character and can be the cause of death of the host [e.g., cases known from history of people being "eaten alive by worms" (i.e., fly larvae)]; tissue myiasis, in particular wound myiasis, is caused by both obligate (larvae of the Wohlfahrt fly) and facultative parasites [larvae of the blowfly (Lucilia), the housefly (Musca domestica) (Fig. 4), the flesh fly (Calliphora), Cochliomyia macellaria, Pycnosoma, etc.]. - II. Cavity myiasis. Larvae can be located: 1) In the nasal cavity (nasomyiasis), where they sit on the mucous membrane [larvae

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Figure 1. Myxoglobulosis. Figures 2 and 3. Destruction of soft tissues by fly larvae. Figure 4. Infection of a guinea pig with a culture of Tr. gypseum by rubbing into the skin of the back. Figure 5. Hematogenous fungal infection experimentally induced in a guinea pig with a culture of Tr. gypseum (12th day). Figure 6. Microsporia.

Figure 6. Various phases of penetration of the Cordylobia larva under the skin.

of the sheep botfly (Oestrus ovis), the nasal botfly of horses (Rhinoestrus purpureus)] or burrow into the soft tissues and destroy them (Wohlfahrt fly). 2) In the oral cavity - in the gums, destroying their soft parts (e.g., the Wohlfahrt fly); this phenomenon is apparently so frequent that among the common people toothache was etiologically associated with the presence of "worms" in the mouth. 3) Of the ear canal (otomyiasis) - Wohlfahrt fly, etc.; myiasis here usually develops on the basis of some ear diseases; larvae can destroy the eardrum, middle ear, penetrate into the mastoid process, venous sinus, and reach the meninges (consequences - up to a fatal outcome). 4) Of the urinary tract and bladder - larvae of Anthomyia (Fannia) canicularis, Musca domestica. 5) Of the genital organs - larvae of the Wohlfahrt fly (in the genital slit of sheep). - III. Ocular myiasis (ophthalmyiasis) - larvae in the conjunctival sac of the eye (Oestrus ovis, Rhinoestrus purpureus, and the Wohlfahrt fly in humans; the latter is especially dangerous, since its larvae can perforate the wall of the eyeball and completely destroy the eye). - In all these cases, infection of the host occurs passively: some flies deposit their larvae in his cavities, into the eye, into ulcers, or wounds; others deposit eggs there, from which larvae hatch already in the host's organism; the larvae of some species (Cordylobia) (Fig. 6) actively burrow into human skin; there are examples of even pupated stages being found in the host; therefore, the concept of myiasis extends to all cases of finding any stages of metamorphosis of flies from egg to puparium in or on the host. - IV. Intestinal myiasis is the term for cases of the presence of living fly larvae in the stomach or intestine of man. Symptomatology is diverse. When larvae are localized in the stomach, there is nausea, vomiting, and sharp pain in the epigastric region; when they are found in the intestine, abdominal pain, hemorrhages, and a typhoid state come to the forefront. With prolonged presence of fly larvae in the intestine, colitis develops. Various species of flies can live in the human digestive tract: housefly, flesh fly, blowfly, cheese skipper (Piophila casei), Anthomyia (Fannia) canicularis, Anthomyia scalaris, Eristalis, Philaematomyia, etc. The diagnosis of intestinal myiasis must be made with caution in order to distinguish true cases of myiasis from false ones. The latter include cases where patients deliberately mislead the physician by bringing in "parasites" allegedly coming from the intestine; further, when collecting feces from the ground for study, foreign objects, including fly larvae, may be accidentally captured; finally, flies may lay eggs in already passed excrement, and larvae may manage to hatch from the eggs before the feces reach the physician for study; in the latter case, all larvae will be very small in size (about 1 mm), whereas adult larvae reach 1-1½ cm in length, and sometimes more. - Infection of the digestive tract with larvae occurs as a result of swallowing them with food or with some other material. Larvae of the cheese skipper (Piophila casei) live in salted fish, cheese, and can be easily eaten; other flies can lay eggs in already prepared food (e.g., boiled meat), and larvae develop on the same substrate. Cases of receiving larvae with vegetables, etc., are frequent. Treatment of cutaneous myiasis consists in removing botfly larvae from the passages they make, extracting these larvae from wounds and ulcers, applying tampons with chloroform, antiseptic treatment of ulcers and wounds; from the eye, botfly larvae are removed with tweezers or by washing, from the stomach - by washing, from the intestine - with various anthelmintics. - Prophylaxis of myiasis: treatment of ulcers on the body of domestic animals to destroy fly larvae in them, treatment of ulcers and wounds so that their purulent discharge does not attract flies, protection of food products from flies, consumption of well-washed and peeled vegetables, especially if the latter are used fresh; burning of corpses and carrion.