Flies

Development and feeding features

The life cycle of flies critically depends on ambient temperature, humidity, and the degree of substrate aeration. When the larva finishes its growth, it stops feeding and migrates to cooler and drier areas of the soil for pupation (formation of the puparium). Hatched adults move toward the surface of the ground using a special organ called the ptilinum (frontal sac).

The insects' diet is extremely diverse: they consume food and plant residues, animal and human excreta, while hematophagous species feed on blood and lymph. The high epidemiological hazard of flies is associated with their feeding behavior. They are highly mobile, constantly crawling from place to place and feeding repeatedly, even when fully sated. The feeding process is accompanied by frequent defecation and a characteristic regurgitation phenomenon, through which a mass of pathogenic microorganisms gets onto human food.

Classification by habitat

Depending on the degree of association with humans, adult individuals are divided into two ecological groups:

• Endophilic (synanthropic): They spend almost their entire lives inside human dwellings or livestock facilities. It is synanthropes, which include most representatives of the family Muscidae, that play a major role in the spread of infections.
• Exophilic: They live in open nature, and fly into living quarters only as a rare exception.

Flies as disease vectors

Synanthropic insects (including not only flies, but also cockroaches — the German cockroach Blattella germanica and the oriental cockroach Blatta orientalis) are active mechanical vectors of intestinal infections. Pathogens are carried on the feet, body surfaces, and inside the intestine.

Main representatives and their significance:

1. Housefly (Musca domestica): The most significant mechanical vector of pathogens of dysentery, typhoid fever, cholera, tuberculosis, diphtheria, as well as protozoan cysts (Giardia, amoebae) and helminth eggs.
2. Bazaar fly (Musca sorbens): Specific to hot countries, mechanically carries pathogens of eye infections and leprosy.
3. Stable fly (Stomoxys calcitrans): An obligate hematophage that breeds in manure and rotting hay. It attacks livestock and humans, mechanically transmitting anthrax and tularemia.
4. Tsetse fly (genus Glossina): A viviparous insect (larvae mature directly in the female's uterus). It is a specific vector of trypanosomes, the causative agents of African sleeping sickness.

Pathogens of myiasis

Larvae of certain species of flies are capable of penetrating the human and animal body, causing parasitic lesions known as myiasis.

• Accidental myiasis (more often intestinal) is provoked by ingested larvae of the false stable fly (Muscina stabulans), as well as green and blue bottle flies.
• Benign myiasis is caused by larvae of various botflies (subcutaneous, gastric, nasopharyngeal), which are obligate parasites.
• Malignant myiasis is caused by the Wohlfahrt fly (Wohlfahrtia magnifica), which inhabits the pastoral regions of Central Asia and the Caspian region. This is an exophilic species that never flies into houses. Infection occurs in the field, often when a person is sleeping outdoors. The female lays from 120 to 160 microscopic larvae into abrasions or the mucous membranes of the eyes, nose, or ears. The larvae act as aggressive endoparasites, penetrate into the subcutaneous tissue, and feed on the host's living tissues for 5 days, after which they drop to the ground, usually at night, to pupate.

Briefly: answers to topical questions

What else to study on this topic

• Mechanisms of pupation and structure of the ptilinum in dipterans
• Pathogenesis of malignant myiasis and methods of its surgical treatment
• Life cycle of the tsetse fly: features of viviparity
• Differences between biological (specific) and mechanical transmission of infections
• Synanthropic cockroaches as mechanical vectors of pathogens

Other topics in the "Medical Arachnoentomology" section

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