BASICS OF MEDICAL BIOLOGY - 2012

Medical Arachnoentomology

Medical arachnoentomology is a branch of medical parasitology that studies members of the phylum Arthropoda of medical importance. They are generally categorized into the following groups: 1) agents of parasitic human diseases (e.g., Scabies, demodicosis, myiasis); 2) vectors of various human diseases (infectious, vector-borne, nematodal); 3) mechanical vectors of parasitic life stages (cysts, eggs, etc.) affecting humans; 4) hematophagous species (mosquitoes, sandflies); 5) venomous Arthropods (scorpions, spiders, Hymenoptera).

Class="center">Phylum Arthropoda

The phylum Arthropoda is the largest animal group in the world, encompassing over 1 million species. Phylogenetically, arthropods evolved from annelid worms. Their key characteristics include: 1) bilateral Symmetry; 2) triploblastic development, meaning the presence of three germ layers in the embryo; 3) heteronomous body segmentation, where body segments vary in Structure and function; 4) tagmosis, or the fusion of segments into distinct body regions (HEAD, Thorax, abdomen, though variations exist: cephalothorax and abdomen in crustaceans and arachnids, or complete fusion of all regions in mites and ticks); 5) jointed appendages operating as multi-articulated levers; 6) Muscle differentiation featuring striated musculature; 7) an external chitinized exoskeleton that provides environmental protection and serves as an attachment site for Muscles; 8) a hemocoel, or mixed body cavity, formed during embryonic development through the merging of the Primary and secondary coelomic cavities; 9) well-developed Organ Systems: digestive, respiratory, circulatory, nervous, endocrine, and reproductive.

The Digestive System consists of three regions: the foregut, midgut, and hindgut, terminating in an anus. The midgut is associated with digestive glands.

Respiratory Organs vary according to habitat: aquatic forms possess gills capable of utilizing dissolved oxygen, whereas terrestrial forms rely on Lungs and tracheae.

Excretory organs differ structurally across classes. In some, they are highly modified metanephridia (such as the excretory glands of crustaceans), while others feature a novel type of excretory structure — Malpighian tubules (found in arachnids and insects).

The Circulatory system is advanced due to the presence of a pulsating organ, The Heart, located on the DORSAL SIDE OF the body. However, unlike Annelids, arthropods have an open circulatory system. The Blood — hemolymph — does not take part in respiration.

The Nervous System is of the ganglionic type (ventral nerve cord). It is represented by a cerebral ganglion, circum-pharyngeal connectives, and a ventral nerve chain. Notably, arthropod evolution involved the fusion of nerve ganglia, particularly within the head and thoracic regions.

In addition to the nervous system, Endocrine glands play a regulatory role, controlling metamorphosis and environmental adaptation.

The Reproductive System. Arthropods reproduce exclusively sexually; they are dioecious, and most species exhibit external Sexual Dimorphism.

The similarities between arthropods and annelid worms point to their phylogenetic relationship. Key progressive features (aromorphoses) of arthropods compared to annelids include heteronomous metamerism, The Emergence of jointed appendages, a more advanced Muscular System, a complex nervous system, The Development of a heart, and an external chitinized exoskeleton that protects the body and anchors muscles.

Arthropods are characterized by numerous adaptations to diverse environmental conditions, alongside A wide variety of respiratory, feeding, and locomotory structures.

Classification. The phylum Arthropoda is divided into several classes, of which three hold medical significance: Crustacea, Arachnoidea, and Insecta.

Class Crustacea

This class comprises about 25,000 species inhabiting primarily marine and freshwater ecosystems. It is divided into two subclasses: Entomostraca (lower crustaceans) and Malacostraca (higher crustaceans).

Lower crustaceans (such as Daphnia, Cyclops, and Diaptomus) inhabit the pelagic zone and form part of the plankton. A defining feature is their long, branching antennules, which help keep the organisms afloat and aid in locomotion, accompanied by a single, unpaired simple eye. They play a vital role as a primary food source for numerous fish and cetaceans, and also contribute to the self-purification of bodies of Water. Medical importance: Cyclops and Diaptomus serve as intermediate hosts for helminths such as the broad fish tapeworm (Diphyllobothrium latum) and the Guinea worm (Dracunculus medinensis).

Higher crustaceans inhabit marine and freshwater environments (freshwater crayfish, crabs, lobsters, spiny lobsters, shrimp, hermit crabs). Only woodlice and certain crabs (such as the coconut crab) live terrestrially. Medical importance: freshwater crayfish and crabs in East Asia and the Russian Far East act as intermediate hosts for the lung fluke (Paragonimus ringeri).

Fig. 77. Cyclops (Cyclops strenuus), female:

1 - eye; 2 - antennule; 3 - antenna; 4 - cephalothorax; 5 - free thoracic segments; 6 - abdominal segments; 7 - caudal rami; 8 - egg sac; 9 - intestine; 10 - Ovary; 11 - longitudinal thoracic muscles.

Class Arachnoidea

This class brings together approximately 35,000 species adapted to terrestrial life. The body consists of two tagmata: the cephalothorax and the abdomen. The degree of segmentation varies: solifuges show the most distinct segmentation; in scorpions, only the abdomen is segmented; in spiders, the abdomen lacks segmentation; while in most mites and ticks, the body regions are fused into a single mass.

Integument and Locomotor Apparatus. The body is covered by a chitinized cuticle backed by a hypodermis. Hypodermal derivatives include silk and venom glands. A distinctive feature is the presence of six pairs of appendages: the first two pairs (chelicerae and pedipalps) are adapted for capturing and crushing food, while the remaining four pairs serve as walking legs. During embryonic development, several pairs of abdominal appendages begin to form, but they subsequently develop into spinnerets.

The digestive system is adapted to feeding on semi-liquid food; digestive Enzymes are injected into the prey's body and, after its Tissues are digested, are absorbed by the predator. The Pharynx of arachnids Functions as a sucking apparatus.

The Respiratory system is represented either by book lungs or tracheae, which open to the outside through pores called spiracles. The pulmonary sacs contain numerous leaflet-like folds housing blood capillaries (homologous to the gills of crustaceans). Tracheae are a system of branching tubes that extend directly to all organs, where tissue gas exchange takes place.

The excretory system. Some arachnids possess modified metanephridia, while others have Malpighian tubules, which are outgrowths of the gut (at the border of the Midgut and Hindgut) located in the body cavity. Metabolic waste products pass from them into the hindgut.

The circulatory system. It is most complex in scorpions and spiders, which feature pulmonary respiration similar to that of crustaceans. The circulatory system has a simpler structure in arachnids that respire via tracheae; in mites and ticks, it may be entirely absent or consist of a sac-like heart and a pair of ostia (openings).

The nervous system is characterized by the concentration of its constituent parts. In some forms, the ventral nerve cord fuses into a single cephalothoracic ganglion.

All arachnids are dioecious. Sexual dimorphism is well expressed.

The most important orders of arachnids of medical significance are Solpugae, Scorpiones, Araneae, and Acarina.

Order Solpugae, or solifuges (Solpugae). Solifuges belong to arachnids with a highly segmented body. The chelicerae resemble pincers, while the pedipalps, which function as tactile organs, are leg-like and participate in locomotion. Solifuges are predators. Their primary weapon of attack is their well-developed chelicerae. Solifuges lack venom glands, but their bites are painful and can be complicated by inflammatory processes because the wound sites are contaminated with food particles adhering to their pubescent chelicerae. The respiratory organs are tracheae. They are nocturnal in habit. They are distributed in Central Asia, the Caucasus, the Crimea, and Moldova. The solifuge (Galeodes araneoides), found in the Crimea and the Caucasus, reaches up to 5 cm in length.

Fig. 78. Solifuge (Galeodes araneoides):

1 - chelicera; 2 - pedipalp; 3 - walking legs; 4 - posterior thoracic segments; 5 - abdomen; 6 - cephalothorax; 7 - eyes.

Order Scorpions (Scorpiones). More than 1,500 species are known. They inhabit hot and warm Regions of the globe. In Ukraine, in the southern Crimea, a single endemic species dwells—the Crimean scorpion (Euscorpius tauricus); its size is 5–10 cm. The body consists of an unsegmented cephalothorax and a long segmented abdomen. The pedipalps are pincer-like. The abdomen comprises a broad preabdomen and a narrow postabdomen, which is improperly referred to as the "tail." The terminal segment of the abdomen ends in a swollen telson, which houses two venom glands and bears a sharp, claw-like spine—the sting.

The ducts of the venom glands open at the tip of the sting. The venom apparatus serves for subduing prey and defending against enemies. They are predators. By day, they hide under stones, in wall crevices, and under tree bark, emerging at night to search for prey, which they kill with a sting by arching their postabdomen over their back toward the victim, held firmly by the pedipalps. They feed mainly on arthropods. Most species are viviparous, with the female carrying the young on her back for some time.

Medical significance. Scorpions are venomous animals. Scorpion stings from species living in Ukraine are generally not fatal to humans, but they cause severe pain and Swelling that can spread over a considerable distance. In severe poisonings, intoxication develops—manifested by difficulty breathing and swallowing, nausea, and even convulsions. All these symptoms last for several days. Stings from large tropical species (17 cm) can result in death. Specific anti-scorpion serum is used for therapeutic purposes.

Prophylaxis. When camping in tents, it is necessary to carefully inspect bedding and footwear, and to shake out clothing.

Fig. 79. Scorpion (Buthus eupeus); ventral view:

1 - chelicerae; 2 - pedipalp; 3 - anus; 4 - spiracle; 5 - telson; 6 - preabdominal segment; 7 - postabdominal segment; 8 - leg; 9 - sting.

Order Spiders (Araneae). Over 20,000 species are known. Sizes range from 0.8 to 11 cm. Males are generally smaller than females. The body consists of an unsegmented cephalothorax and an abdomen connected by a narrow pedicel. There are six pairs of appendages: chelicerae, pedipalps, and four pairs of walking legs. The chelicerae terminate in a movable claw-like segment, near the apex of which is the opening of the venom gland duct. In males, the pedipalps function as copulatory organs. Three pairs of spinnerets, where silk glands open, are located at the posterior end of the abdomen. The digestive organs are adapted to feeding on semi-liquid food. Development is direct. After mating, the female often devours the male if he fails to escape. Spiders are predators, feeding on arthropods. They kill their prey with venom. The black widow and tarantula are of medical importance.

Black widow (Latrodectus tredecimguttatus). The black widow is a fatally venomous spider. In Ukraine, it is found in the Odesa and Mykolaiv regions and the steppes of the Crimea. The female is 1.5–2 cm long. Her abdomen is globose, velvety black with red spots. The male is smaller—no more than 1 cm. His abdomen is elongated, with bright white spots and reddish dots in the center.

The female deposits eggs into cocoons (5–6) On the surface of the ground and stays close by. The young hatch inside the cocoon but do not leave it until spring. They reach sexual maturity in June and disperse across the area. A second dispersal (second migration) occurs after copulation. They are especially dangerous during Migrations.

Medical significance. Black widow bites are fatal to humans and animals (camels, horses, cattle). However, sheep and pigs consume black widows without harm to themselves, so they can be used to clear pastures of these spiders. The venom exhibits neurotoxic action. A bitten person experiences acute pain that rapidly spreads throughout the entire body. The abdominal wall muscles are rigid, and patients adopt a characteristic doubled-up posture. Symptoms of general intoxication include asphyxia, palpitations, accelerated pulse, headache, vomiting, sweating, and urinary and fecal retention in patients. Initially, there is characteristic excitation followed by deep depression, clouded consciousness, a sense of fear, and sometimes hallucinations. Black widow venom is 15 times more toxic than rattlesnake venom. Anti-black widow serum is administered for Treatment, which rapidly halts intoxication.

Fig. 80. Black widow: female (1) and male (2).

Prophylaxis. Avoid sleeping outdoors in habitats of black widows, especially during their migration period. In populated areas, it is recommended to clear weeds in yards and along tram lines where black widows find shelter.

Tarantula (Lycosa singoriensis). A venomous spider measuring 3–4 cm in length with a yellowish-brown body. It is a ground-dwelling species that burrows deep vertical tunnels (up to 30 cm). Its bite is painful but poses no danger to humans. The bite site develops hyperemia and occasionally significant edema. The pain persists for a day and, unlike the bite of the black widow (karakurt), does not radiate to other PARTS OF THE body.

Order Acarina (Ticks and Mites). Mites and ticks constitute a highly diverse group within the class Arachnida, with up to 10,000 known species. A significant portion of this group comprises blood-sucking species that parasitize animals and humans. These arachnids are small, sometimes microscopic in size. The body is divided into two tagmata: the gnathosoma (a small head region) and the idiosoma (the trunk proper). In some species, the body is unsegmented and lacks distinct tagmata. They possess six pairs of appendages. The first two pairs (chelicerae and pedipalps) are modified into a proboscis (mouthparts) adapted for grasping and crushing food, featuring either piercing-sucking or chewing-sucking mouthparts. The remaining four pairs are walking legs attached to the ventral surface of the body by fixed coxae. Respiration occurs via tracheae, although respiratory organs are reduced in some species. The digestive system of blood-sucking species is extensively branched, particularly in females, where the midgut features lateral diverticula (ceca).

Development proceeds through metamorphosis. The fertilized female lays eggs that hatch into larvae possessing three pairs of legs. The larva molts into a nymph which, like the adult form, has four pairs of legs but lacks a genital aperture. There may be multiple nymphal instars. Following the final molt, the nymph develops into the sexually mature adult (imago). While most species are oviparous, some are viviparous.

Fig. 81. Stages of tick development (Taiga tick):

a – larva; b – nymph; c – adult male (dorsal view); d – adult female (dorsal view).

The organisms upon which ticks feed are referred to as hosts. Ticks may be one-, two-, or three-host species. In one-host ticks, all developmental stages occur on a single host. In two-host species, the larva and nymph feed on one host, while the adult feeds on another. In three-host ticks, each active stage feeds on a different host, which can significantly prolong the developmental cycle.

Of greatest medical importance are the itch mite, the Hair follicle mite (both belonging to the order Acariformes), as well as ixodid, argasid, and gamasid ticks, which belong to the order Parasitiformes.

Itch mite, or scabies mite (Acarus siro, syn. Sarcoptes scabiei) – the CAUSATIVE AGENT OF scabies, an intraepidermal parasite.

Geographic distribution – cosmopolitan (worldwide).

Localization – the stratum corneum of the epidermis.

Morphology. An extremely small mite: the female measures approximately 0.3 mm, and the male about 0.2 mm in length. The body is oval with transverse cuticular folds, bearing scales and long backward-directed setae. The legs are greatly shortened, an adaptation to burrowing within the Skin. Eyes are absent. Respiration occurs through the entire body surface. The mouthparts are of the chewing type.

Fig. 82. Itch mite (Sarcoptes scabiei):

a – female, dorsal view, containing 2 eggs; b – mite burrow in human skin, showing eggs at various Selection/3.html">Stages of development and the female mite at the terminal end of the burrow.

Life cycle. The mode of transmission is primarily contact-fomite, occurring through direct contact with an infected person or by sharing personal items that may harbor the mites. To penetrate the skin, the mite prefers delicate areas (interdigital spaces, axillae, abdomen). The length of the burrow excavated by a female in a single day reaches 2–3 mm (males do not burrow). The female creates ventilation holes along the length of the burrow. Throughout her lifespan (40–45 days), a female lays 20 or more eggs. The female is typically located at the blind terminal end of the burrow. Larvae hatch from the eggs within 3–5 days. The larvae molt into nymphs, which then migrate to the skin surface, molt again, and develop into sexually mature adults. Following Fertilization, the males die, whereas the females burrow back into the skin. They feed on epidermal Cells.

The primary symptom of the disease is pruritus (itching), which intensifies in the evening and at night when the mite's activity increases. Scratching ruptures the burrows, dispersing mites, larvae, and nymphs across the patient's body, bed linens, and surrounding objects.

The source of scabies infection is an infected human. Domestic and wild mammals also contract scabies caused by other species of itch mites. Humans can occasionally be parasitized by scabies mites originating from horses, dogs, pigs, sheep, goats, camels, wolves, and other animals.

Pathogenic effect. Scabies is a parasitic anthroponotic disease characterized by epidermal lesions and intense itching. The skin exhibits burrows appearing as straight or tortuous lines resembling healing scratches.

Laboratory Diagnostics – identification of the itch mite via microscopic examination of material scraped from the burrows.

Prevention. Individual prophylaxis involves maintaining personal hygiene, clean clothing, and living quarters, alongside strict sanitary precautions after contact with infected individuals or animals. Public health measures include the detection and treatment of cases, sanitary inspection of dormitories and bathhouses, and health education.

Hair follicle mite (Demodex folliculorum) – the causative agent of demodicosis.

Geographic distribution – cosmopolitan.

Localization – Sebaceous Glands and hair follicles.

Morphology. The follicle mite has an elongated, worm-like body. Its anterior end bears four pairs of short, jointed legs, each terminating in two claws. Mite dimensions: females are about 0.4 mm long, and males about 0.3 mm. A dorsal shield covers the anterior portion of the dorsum, behind which the body exhibits transverse striation.

A single sebaceous gland can harbor up to 200 mites. The source of infection is an infected person. The transmission route is direct contact or through household items: via contact with an infected person, or through bedding, towels, and clothing contaminated with the follicle mite.

Fig. 83. Follicle mite.

Pathogenic effect. Acne, rashes, inflammatory purulent areas, seborrhea, and dermatitis appear on the skin. With a prolonged course of the disease and massive infestation, the skin becomes wrinkled and hyperemic. Pustules with lymphatic discharge form, and eyebrows and eyelashes fall out.

Laboratory Diagnosis: detection of the follicle mite by microscopic examination of acne contents.

Prevention. Personal: practicing good personal hygiene, avoiding The Use of other people's towels. Public: identification and treatment of patients, health education.

Family Ixodidae (Hard ticks). Hard ticks are temporary ectoparasites of animals and humans. They inhabit mainly forest, forest-steppe, and steppe zones. Many species are vectors of pathogens of infectious diseases in humans and animals. Furthermore, during feeding, ticks inject toxic substances along with their saliva into the host's body, causing local and sometimes systemic reactions.

The size of unfed adult ticks is 4-5 mm. After blood-feeding, females can reach 10 mm or more. In males, a dorsal scutum covers the entire upper part of the body. In females, nymphs, and larvae, the scutum covers only the anterior part of the body. Behind this scutum, the body is covered with thin Chitin that stretches easily. This allows the female to ingest a large amount of blood, which exceeds her unfed weight by 200-400 times. Males ingest significantly less blood. The capitulum (gnathosoma) consists of a base, a pair of chelicerae, an unpaired serrated plate—the hypostome—and four-segmented palps, which they use to select an attachment site. The hypostome has sharp, backward-pointing denticles. The chelicerae bear powerful hooks. Thanks to these adaptations, the tick's mouthparts are firmly anchored in the host's skin.

Ticks await their prey in the wild, which has led to the development of specific adaptations. For instance, ticks can survive long periods of starvation, but once attached to a host, they feed on blood for an extended period, sometimes for several days. The biting process is painless (at all stages of development) because ticks secrete special anesthetic substances, making their attachment go unnoticed.

Development occurs with metamorphosis and includes 4 stages: egg, larva, nymph, and adult (imago). Transition between stages in blood-sucking ticks is possible only after blood-feeding. Among hard ticks, there are one-host, two-host, and three-host species.

Fig. 84. Mouthparts (capitulum) of a female castor bean tick (Ixodes ricinus): one-, two-, and three-host ticks. In one-host ticks, left - dorsal view; right - ventral view; 1 - cheliceral sheath; 2 - cheliceral hooks; 3 - palp; 4-7 - palp segments; 8 - hypostome; 9 - basis capituli; 10 - porose areas (Sensory Organs).

Mass mortality of ticks is observed at all stages of development. However, females are characterized by high fecundity (they can lay up to 17 000 eggs). They lay eggs on the ground once in their lifetime, after which they die. Adult ticks attack large mammals to feed on blood, after which mating occurs. The fertilized female drops to the ground, begins laying eggs, and then dies.

Hard ticks of the genera Ixodes and Dermacentor are of the greatest medical significance.

Taiga tick (Ixodes persulcatus) is a temporary ectoparasite, vector, and natural reservoir of the pathogen of (spring-summer) taiga encephalitis. The taiga tick is distributed mainly in the taiga east of the Urals, but has also been found in Europe. The size of the male is 2,5 mm, and the female is up to 4 mm. The coloration is brown. It is a three-host tick. Each stage of metamorphosis feeds on blood from hosts of different species. The larva feeds on small vertebrates (rodents, hedgehogs, birds), then enters the soil and molts there. Nymphs feed on chipmunks, squirrels, and hares. Hosts of adult forms include cattle, elk, and deer. Adult ticks also attack humans. The complete development cycle from egg to mature stage takes at least three years.

Fig. 85. Circulation of the taiga encephalitis virus in nature:

the virus—the pathogen of taiga encephalitis—is indicated by crosses in the diagram; vectors of the virus—the taiga tick, wild mammals, and birds inhabiting the taiga—are Components of the natural focus. Humans and domestic animals become infected through the bites of infected ticks.

Taiga encephalitis is a severe, viral, naturally focal, vector-borne disease accompanied by Brain damage and high mortality. Transmission of the virus among animals, and from them to humans, occurs through the bite of an infected taiga tick. An infected female tick transmits the virus to her offspring through the eggs—transovarially. By harboring the virus in their bodies and transmitting it to their offspring over several generations, ticks serve not only as vectors but also as a natural reservoir for the pathogen of taiga encephalitis.

In the 30-х years, members of special expeditions led by Academician E.N. Pavlovsky clarified The Role of the taiga tick in the Epidemiology of encephalitis and developed preventive measures. Virologists participating in these expeditions, led by L.A. Zilber, discovered the pathogen (virus) of taiga encephalitis. Based on this work, a preventive vaccine was developed. The discovery of natural foci of taiga encephalitis allowed E.N. Pavlovsky to formulate The Doctrine of the natural focality of vector-borne diseases.

Prevention. Personal: protection against tick bites (special clothing, repellents), and inspection of clothing and body to remove attached ticks. Public: eradication of ticks in their primary habitats frequently visited by people using chemicals (acaricides), and preventive vaccinations.

Castor bean tick (Ixodes ricinus). The castor bean tick is a temporary ectoparasite and a vector of pathogens causing tularemia and spring-summer encephalitis. It parasitizes both livestock and wild animals and can attack humans. It is distributed in the forest and forest-steppe zones of Europe. In size, structure, and life cycle, it is similar to the taiga tick.

Dermacentor pictus is a temporary ectoparasite and a vector of tularemia pathogens. It is distributed in the forest zone.

D. marginatus is a temporary ectoparasite and a vector of pathogens causing tularemia and brucellosis. It is distributed in the steppe zone.

Argasid ticks (Argasidae). Soft ticks are distributed mainly in semi-desert and desert areas. Unlike hard ticks, they lack a scutum. The body is covered with irregular chitin with a characteristic margin along the entire edge of the body. The mouthparts are located ventrally in a special depression and are not visible from the dorsal side. They live in closed biotopes (caves, burrows, mud-brick buildings). They are better protected from adverse conditions and suffer lower mortality than hard ticks, so they lack adaptations for intensive reproduction. A female lays only hundreds, or sometimes dozens, of eggs. On the other hand, these ticks must make do with prey that enters their shelter, and their host range is very broad (vertebrates from reptiles to humans). They have developed The ability to feed rapidly while the host is in the shelter. Blood-feeding lasts from 3 to 30 minutes. Since feeding is less abundant, fewer eggs mature, but the female lays them several times throughout her life. Because the biotope may go unvisited by hosts for long periods, the ticks can starve for years; therefore, as shown by E.N. Pavlovsky, their development can extend up to 20-28 years. The development cycle includes several nymphal stages (from 2 to 7). The settlement tick has the greatest medical significance.

Fig. 86. Settlement tick: male (dorsal view).

The settlement tick (Ornithodorus papillipes) is a temporary ectoparasite and a vector of the pathogens of tick-borne relapsing fever (spirochetes). Tick-borne relapsing fever is a natural-focal vector-borne zoonotic disease. Natural reservoirs of the spirochetes include various rodent species, bats, and the settlement tick itself, which temporarily parasitizes them; the female tick is capable of transmitting the pathogen to its offspring transovarially. Humans become infected through the bites of infected ticks.

Geographical distribution - Central Asia, Afghanistan, Iran, India.

Morphophysiological characteristics. The settlement tick is dark gray in color. The female is 8.2 mm long, and the male is 5.8 mm. Eyes are absent. Adult ticks can fast for up to 13 years.

Prevention of tick-borne relapsing fever. Personal prevention involves protecting oneself from tick bites, avoiding prolonged stays in caves, adobe buildings, and other tick biotopes, and using repellents. Public Prevention includes the eradication of ticks and rodents. The most effective measure is the demolition of old, tick-infested adobe buildings, replacing them with European-style houses.

Family Gamasid mites (Gamasoidea). A large group of small mites, 0.3 to 4 mm in length. Some gamasid mites are permanent, while others are temporary ectoparasites of birds and mammals. Gamasid mites that parasitize birds (swallows, swifts, chickens, pigeons) and rodents are of medical importance. From these hosts, the mites transmit viral pathogens to humans.

Class Insecta (Insects)

This is the most numerous class of the phylum Arthropoda, which unites all Trachea-breathing arthropods with three pairs of limbs. The Study of insects is called entomology.

The insect body is divided into three regions: the head, thorax, and abdomen. On the head, There is a pair of jointed antennae, mouthparts, a pair of compound eyes, and often simple eyes (ocelli). The mouthparts consist of three pairs of appendages: a pair of mandibles (upper jaws) and two pairs of maxillae (lower jaws). The second pair of maxillae fuses to form the lower lip (labium). The upper lip (labrum) is a chitinous outgrowth. The Tongue (hypopharynx) is a chitinous PROJECTION OF THE floor of the Oral Cavity. Depending on feeding habits, the following types of mouthparts are distinguished: chewing, piercing-sucking, and sponging.

The thorax consists of three segments, each bearing a pair of legs (hence, hexapods). Depending on environmental conditions and adaptations to different modes of locomotion, the legs can be walking, running, jumping, swimming, or digging. In flying insects, wings are attached to the second and third, or only to the second, thoracic segment; these are membranous integumentary outgrowths permeated by tracheal tubes (Veins). In some insects, the second pair of wings is reduced, leaving remnants called halteres, which serve as equilibrium organs. Wingless insects are also known. They are divided into primary and secondary wingless groups. Primary wingless insects are ancient species whose lack of wings is evidence of a primitive Organization. Secondary wingless insects lost their wings due to a parasitic lifestyle (fleas, lice).

The body wall (integument) is represented by a chitinized cuticle, hypodermis, and basement membrane. The musculature is highly differentiated and composed of striated muscles. Integumentary derivatives include various glands: venomous, wax, scent, and silk-spinning glands. The body cavity is a mixocoel filled with hemolymph.

The digestive system consists of the oral cavity with Salivary Glands, pharynx, Esophagus, crop, gizzard, midgut (often with pyloric caeca), and hindgut ending with an anus.

Excretory organs are Malpighian tubules (which empty into the hindgut) and the fat body (which accumulates metabolic waste products).

Respiratory organs are tracheae (a system of branched tubes of various diameters) that open via respiratory spiracles (stigmata). The terminal tubules (tracheoles) penetrate even into individual cells. Thus, the respiratory system performs the function of the circulatory system in transporting oxygen directly to the tissues.

The circulatory system is relatively poorly developed due to the peculiarities of the respiratory system. It is open. The Heart and aorta are located on the dorsal side. Hemolymph circulates through the system.

The nervous system consists of the supraesophageal and subesophageal ganglia, circumesophageal commissures, which together form the nerve ring, and a ventral nerve cord. The supraesophageal ganglion, often referred to as the brain, is highly developed. Sensory organs—Touch, smell, Vision, taste, and Hearing—reach a high level of development. Insects exhibit complex behaviors based on instincts.

Reproduction is exclusively sexual; insects are dioecious and exhibit well-defined sexual dimorphism (differences between females and males). Postembryonic development is either direct (in lower insects) or via metamorphosis (transformation): incomplete metamorphosis (egg-larva-imago) and complete metamorphosis (egg-larva-pupa-imago).

Medical importance. Among insects, there are: 1) vectors of pathogens, including those causing widespread epidemics; 2) ectoparasites; 3) venomous insects; 4) causative agents of diseases. The following orders are of the greatest medical importance: order Lice, order Fleas, order Bugs, order Cockroaches, order Diptera.

Order Lice (Anoplura). Wingless, blood-sucking insects. Highly host-specific parasites of mammals. Each species parasitizes a specific host and does not transfer to individuals of other species. The head louse, body louse, and pubic louse parasitize The Human Body.

Fig. 87. Human lice:

a - head louse, male; b - female; c - nit (egg) of the head louse; d - body louse, male; e - nit of the body louse; f - pubic louse; g - nit of the pubic louse; 1 - egg; 2 - operculum; 3 — cement substance.

The head louse (Pediculus humanus capitis).

Localization - scalp.

Morphology. Grey-coloured insects. The male is 2-3 mm long, the female is 3-4 mm. The body is dorsoventrally flattened and consists of a head, thorax, and abdomen. On the head, there is a pair of short, thick antennae, a pair of simple eyes (sometimes absent), and piercing-sucking mouthparts, which are retracted into the head at rest and are not visible from the outside. The thoracic segments are fused and bear three pairs of legs. The tarsus has a movable claw with which lice cling to hair. Wings are absent. There are deep indentations along the sides of the abdomen. The last abdominal segment is bifurcated in females and rounded in males. In males, the copulatory apparatus is visible at the end of the abdomen.

Life cycle. Development with incomplete metamorphosis (egg-nymph-adult). Eggs (nits) are glued to the hair by the secretion of cement glands. The entire development takes place on the human body. A nymph hatches from the egg and, after three molts, transforms into an adult. Both nymphs and adults feed on blood. The lifespan of an adult louse is 27-38 days. During this time, the female lays up to 150 eggs. Development from egg to sexually mature stage takes 2-3 weeks.

Medical significance. The head louse is a permanent human ectoparasite and the causative agent of pediculosis (lice infestation). Louse bites are accompanied by itching, scratching, and skin irritation. Severe infestation can lead to The formation of the so-called plica polonica (matted hair). However, the primary medical Significance of the head louse is that it is a specific vector of the pathogens of epidemic (louse-borne) relapsing fever and, less commonly, epidemic typhus. The pathogens of endemic relapsing and typhus fevers are transmitted by ticks and mites.

The pathogen of epidemic typhus (Rickettsia prowazekii) is found in the louse's gut, where it enters with the patient's blood. The Development of the pathogen in the louse's body takes 4-7 days, after which it is capable of spreading the disease. Human infection occurs when louse feces are rubbed into the bite site. The pathogen of louse-borne relapsing fever (Spirochaeta obermeieri) is found in the louse's hemolymph, where it enters from the louse's gut during feeding on an infected person. A sufficient number of spirochetes to infect a human appears from day 5-6, with the maximum number from day 8-21 after the louse becomes infected. Human infection occurs when the louse is crushed and the hemolymph is rubbed into the blood while scratching the bite site. This method of infection is called contamination.

Prevention. Personal: to prevent pediculosis, it is necessary to wash the body regularly while changing underwear, and to keep clothes and housing clean. Public: detection and treatment of pediculosis, sanitary surveillance of public gathering places (railway stations, hotels, trains, steamships, public baths, barber shops/hair salons); periodic screenings for pediculosis in kindergartens and schools; health education.

Body louse (Pediculus humanus humanus).

Localization - underwear, clothing; moves to the body to feed on blood.

Morphology and life cycle. In appearance and development, it is very similar to P. humanus capitis. Currently, they are classified as different subspecies of the same species, P. humanus. It is larger: the male is 2.1-3.75 mm long, the female is 2.2-4.75 mm. The body is light grey or whitish. Distinctive external features include shallower indentations along the margin of the abdomen, less pronounced pigmentation of the lateral abdominal segments, and thinner, longer antennae on the head. Development is with incomplete metamorphosis (egg-nymph-adult). It glues its eggs to The surface of clothing. All stages of development occur on humans. The lifespan is up to 48 days. During this time, the female lays 300 eggs—twice as many as the head louse. The development cycle lasts up to 16 days.

Medical significance. The body louse is a permanent human ectoparasite, the causative agent of pediculosis, and a specific vector of the pathogens of epidemic (louse-borne) typhus and relapsing fever. The role of the body louse as a specific vector of the pathogen of epidemic typhus was established in 1909 by the French bacteriologist and parasitologist Ch. Nicolle (Nobel Prize, 1928).

Epidemic relapsing fever and epidemic typhus are obligate vector-borne diseases, anthroponoses, which can take on an epidemic character, affecting large populations. In 1874, G. N. Minkh and in 1881, I. I. Metchnikov proved through self-experimentation that the blood of patients with epidemic relapsing fever is infectious. In 1876, O. O. Mochutkovsky established through self-experimentation that the blood of patients with epidemic typhus is also infectious.

Prevention - same as for the head louse.

Pubic louse, or crab louse (Phthirus pubis).

Localization - pubic hair, sometimes eyebrows, eyelashes, underarms.

Morphology and life cycle. The pubic louse is smaller than the head and body lice: males are about 1 mm long, females are 1.5 mm. The body is short and wide, with the thorax and abdomen barely demarcated. The lifespan of an adult pubic louse is 17-26 days. During this time, the female lays about 50 eggs. Development is with incomplete metamorphosis.

Medical significance - a permanent ectoparasite, the causative agent of phthiriasis (Pubic lice infestation). It does not transmit pathogens of other diseases.

Prevention. The same as for other species of lice.

Order Fleas (Aphaniptera). Fleas are wingless, blood-sucking insects, ectoparasites of humans and animals. Typical representatives are the human flea and the rat flea.

Human flea (Pulex irritans). The body is laterally flattened. On the head, there is a pair of simple eyes, short antennae, and piercing-sucking mouthparts. Wings are absent. The hind pair of legs is longer than the others and is of the jumping (saltatorial) type. The abdomen consists of 10 segments; in males, the tip of the abdomen is curved upwards. On the body surface, there are hairs, bristles, spinules, and combs, which are important for Taxonomy.

Development is with complete metamorphosis (egg-larva-pupa-adult). Eggs are laid indoors (crevices, floor cracks, dry debris) or, under natural conditions, in rodent burrows. A legless, worm-like white larva hatches from the egg, feeding on decaying organic matter as well as flea feces. The larva spins a cocoon and pupates. The adult flea lives up to 1.5 years and feeds on blood. Depending on environmental Temperature and humidity, the flea's development cycle lasts from 19 to 270 days.

Medical significance. Flea bites are painful, causing irritation of nerve endings in the skin; a person experiences itching accompanied by scratching, secondary infection, and suppuration. However, their primary significance is that fleas are vectors of the plague pathogen. Plague (syn.: Black Death) is an acute, highly dangerous, naturally focal, facultatively vector-borne disease of bacterial nature. Natural reservoirs of plague include various rodents: rats, tarbagans, ground squirrels, hamsters, gerbils, and voles. The most dangerous are the oriental rat flea (Xenopsylla cheopis), the tarbagan flea (Oropsylla silantiewi), and other fleas. The human flea also transmits the plague pathogen. Fleas become infected when sucking the blood of infected animals. The plague pathogen multiplies in the flea's Stomach, forming a plug that blocks its lumen (the "plague block"). When the flea attempts to feed on blood again, the block prevents blood flow, so the flea regurgitates it into the bite wound, introducing A large number of Bacteria into the host's body. Infection is also possible when a person rubs the feces of infected fleas, along with the plague bacteria, into bite wounds or scratches on the skin. There are other transmission routes as well, which is why plague is classified as a facultatively vector-borne disease. In addition to plague, fleas can transmit the pathogens of endemic typhus fevers, as well as the pathogen of tularemia.

Fig. 88. Human flea (Pulex irritans).

Fig. 89. Flea development:

1 - egg; 2 - larva; 3 - pupa; 4 - cocoon cleared of foreign particles; 5 - normal appearance of the cocoon.

Prevention. Maintaining cleanliness indoors, wet cleaning, and eliminating flea breeding sites such as cracks and crevices in the floor. Insecticides are used to eradicate fleas indoors or on clothing. Under natural conditions, rodents (and consequently fleas) are exterminated in their burrows using pesticides.

Order Hemiptera or True Bugs (Heteroptera). The forewings are partly thickened (hemelytra) and membranous at their free tips. Most species feed on plant sap. Some bugs have transitioned to a parasitic lifestyle. The bed bug and the kissing bug are of medical importance.

Bed bug (Cimex lectularius).

Geographical distribution - cosmopolitan, found worldwide in human dwellings.

Morphology. The body is reddish-brown, dorsoventrally flattened. Females are 6 mm long, males 5 mm. The head features long, segmented antennae, a pair of compound eyes, and piercing-sucking mouthparts. The thorax consists of three segments, each bearing a pair of legs. The dorsal side of the second segment features a pair of rudimentary hemelytra, and behind the third pair of legs are scent glands that emit a characteristic odor. The segmented abdomen of the female is rounded, while that of the male is narrower, with an asymmetrical posterior end containing a notch that houses the sickle-shaped copulatory organ.

Life cycle. Development occurs via incomplete metamorphosis. The female lays eggs in her harborages—crevices in beds, furniture, walls, mattress seams, under wallpaper, and behind picture frames. They reproduce very rapidly. A female can lay up to 12 eggs per day and up to 500 during her lifetime. Bug larvae go through 5 stages, the last of which is called a nymph. The newly hatched larva resembles an adult bug. Both larvae and adults feed on blood. They feed on humans primarily at night. They can survive starvation for long periods (several months). They are highly tolerant of low temperatures, surviving for about 24 hours at — 17 °C. They spread when adults, larvae, or eggs are transported with clothing, furniture, carpets, etc. They often parasitize laboratory animals kept in unsanitary conditions.

Fig. 90. Bed bug (Cimex lectularius): a - female; b - posterior end of female abdomen; c - posterior end of male abdomen; 1 - opening of the copulatory bursa; 2 - copulatory organ.

Medical significance. A temporary human ectoparasite. The bug's saliva contains a toxic secretion, making its bites painful. Redness and swelling occur at the bite site. Their bites disrupt normal human Sleep, which negatively affects health. Vector transmission of pathogens by bed bugs has not been established.

Prevention. Bed bug eggs are destroyed mechanically, while larvae and adults are controlled using insecticides.

Kissing bug (Triatoma infestans) is a vector of the trypanosome (Trypanosoma cruzi), the causative agent of American trypanosomiasis (Chagas disease). It belongs to the family Reduviidae, genus Triatoma. They are large, ranging from 1.5 to 3.5 cm. They are nocturnal. They inhabit wild animal burrows and bird nests. Some species are closely associated with humans, occurring in mud-brick houses and thatched roofs. They are temporary ectoparasites of animals and humans, feeding on blood. When attacking humans, the bugs bite near the eyes or Lips, where the skin transitions to mucous membrane (hence the name "kissing bug"). After feeding, the bug turns 180° and deposits a droplet of feces containing trypanosomes near the bite. These enter either through the bite wound or via scratches on the skin. The infection rate of bugs in trypanosomiasis foci can reach up to 50 %. The primary preventive measure is improving socio-living conditions (building modern housing). Eradication of these bugs is difficult because they parasitize a wide range of animals.

Order Cockroaches (Blattoidea). Over 300 species are known, with about 20 species in Ukraine. Synanthropic species of medical interest include the oriental cockroach (Blatta orientalis) and the German cockroach (Blattagermanica). The former is 20-26 mm in size, while the latter is 8-11 mm. The body is dorsoventrally flattened. The head is directed downwards and almost entirely covered from above by a large, shield-like pronotum. The antennae are setaceous and multi-segmented. The legs are adapted for running. There are two pairs of wings: the forewings are leathery (tegmina), and the hindwings are membranous (folded under the forewings at rest). In male oriental cockroaches, the forewings are developed, while in females they are reduced.

Fig. 91. Kissing bug (Triatoma infestans).

In both male and female German cockroaches, the wings are developed. Postembryonic development occurs via incomplete metamorphosis. They live in human dwellings, particularly in kitchens and garbage chutes. They feed on human Food Products and various organic waste. They are common in cafeterias and dining halls. During the day, they hide in crevices, emerging at night to forage.

Fig. 92. Synanthropic cockroaches:

a - German cockroach (Blatta germanica); b - Oriental cockroach (Blatta orientalis).

Medical significance. Cockroaches act as mechanical vectors of pathogens, primarily gastrointestinal ones. They transmit agents of typhoid fever, dysentery, tularemia, diphtheria, helminth eggs, and protozoan cysts. They may also nibble on the epidermal skin of sleeping individuals.

Order Diptera (True Flies). Dipterans are characterized by having only a single (anterior) pair of wings. The posterior pair is modified into small appendages called halteres, which function as gyroscopic balancers.

Family Culicidae (Mosquitoes). Three mosquito genera are most commonly encountered in Eurasia: Anopheles (malaria mosquitoes), Culex, and Aedes (non-malarial mosquitoes). Only females are hematophagous (blood-feeding). There are about 10 species of the genus Anopheles in Eurasia, the most common being the common malaria mosquito (A. maculipennis). Mosquito biology was most thoroughly studied by V.N. Beklemishev (1890-1962) and his students.

Morphophysiological characteristics. Malarial and non-malarial mosquitoes differ at all developmental stages. Anopheles eggs differ from those of Culex and Aedes not only in shape but also in the way they are laid. Anopheles lay their eggs singly and scattered on the water surface. Each egg is bordered by a concave frill and features lateral floats (air chambers). Culex eggs lack frills and floats, and are laid on the water surface in raft-like clusters. Aedes eggs are laid on damp soil near drying water bodies and, less frequently, on the water surface, either in clusters or scattered.

Culex and Aedes larvae have a respiratory siphon in the form of a tube on the penultimate abdominal segment. Consequently, they hang at an angle in the water, suspended from the surface film by the siphon. Anopheles larvae lack a respiratory siphon and lie horizontally at the water surface.

Pupae are comma-shaped and differ in The structure of their respiratory trumpets. In Anopheles, the respiratory trumpets are funnel-shaped (conical), while in Culex, they are cylindrical.

At the adult (imago) stage, there are differences in the structure of head appendages, wing coloration, and resting posture. In female Anopheles, the maxillary palps are approximately equal in length to the proboscis, whereas in non-malarial mosquitoes, they are short, about 1/3 to 1/4 of the proboscis length. In male Anopheles, the maxillary palps are as long as the proboscis and have club-like swellings at the tips, while in non-malarial mosquitoes, they are usually longer than the proboscis and lack club-like swellings. Antennae are located on either side of the mouthparts. In males, they are plumose (covered with long hairs), while in females, they are pilose (with short hairs). Wing veins are covered with scales that can form spotted patterns. A. maculipennis has 4 dark spots in the middle of the wing, whereas Culex mosquitoes lack such spots. When resting, Anopheles mosquitoes hold their abdomen tilted upward, positioning themselves at an angle to the surface. In other mosquitoes, the body is bent during resting, with the abdomen tilted toward the substrate or parallel to it.

Life cycle and biological features. Development occurs with complete metamorphosis (egg-larva-pupa-imago). Eggs, larvae, and pupae develop in water. The young winged Anopheles mosquito is initially found near water bodies in coastal vegetation. At this time, mosquitoes (both females and males) feed exclusively on plant sap. After a few days, at dusk, males form swarms. A female flies into the swarm and leaves it with one of the males. After fertilization, the female searches for a host and sucks the blood of humans or animals. Blood is essential for egg development. Females possess piercing-sucking mouthparts for blood feeding. In males, the mouthparts are adapted for feeding on plant sap. Anopheles females feed primarily indoors, so they fly from water bodies toward populated areas. The mosquito dispersal zone around anophelogenic water bodies reaches approximately 3 km. After taking a blood meal, the female flies to a shelter and remains there until blood Digestion is complete and the fertilized eggs mature. The female then flies to a water body to lay her eggs. This Life Cycle of the female, from THE START OF blood feeding to egg-laying, is called the gonotrophic cycle (Greek gonos - seed, germ Cell; trophe - Nutrition). After laying eggs, the female seeks a host again to feed on blood. There can be 2-3-6 such cycles during the summer. The lifespan of a female in summer is about 1 month. Males die shortly after mating; their lifespan is only a few days.

Fig. 93. Main differences between malaria and non-malaria mosquitoes:

1 - egg floats of Anopheles; 2 - larval spiracles; 3 - pupal respiratory trumpets; 4 - antennae; 5 - maxillary palps; 6 - proboscis; 7 - eyes; 8 - thorax; 9 - abdomen of an adult mosquito.

For egg-laying, Anopheles use water bodies with standing or slow-flowing water. The number of eggs in a single clutch ranges from 60 to 350. Larvae hatch from the eggs and breathe atmospheric air. Anopheles larvae live exclusively in clean or nearly clean water bodies. Water bodies with a significant amount of organic matter and suspended particles, as well as shaded ones, are unsuitable for them. Therefore, in the control of A. maculipennis mosquitoes, planting trees with large and wide crowns along the banks of water bodies yields good results. The duration of larval development depends on water temperature. Development begins at temperatures no lower than +10° C. The optimal temperature is +25 °C. The minimum period of larval development is 15 days. Larvae feed on bacteria and plant debris, filtering water and swallowing all particles that can pass through the Mouth opening. This biological feature of mosquito larvae is utilized to destroy them by spraying powdered toxic substances on the surface of water bodies. Larvae transform into pupae, and pupae into adults. The most common mosquito in our country, A. maculipennis, was once considered a single species. Today, it is known to include 6 sibling species that differ in several biological characteristics, particularly in their overwintering behavior. In all sibling species of A. maculipennis, fertilized females overwinter. For some, basements serve as overwintering sites where they enter diapause; for others, barns are used, where they feed on animal blood throughout the winter. Males die in autumn.

Fig. 94. Head structure of malaria (Anopheles) and non-malaria (Culex) mosquitoes:

A - Culex; B - Anopheles; 1 - female; 2 - male; a - antennae; b - proboscis; c - palps.

Mosquitoes of the genus Aedes differ from Anopheles in their biological characteristics. The breeding sites for most Aedes species are temporary water bodies: puddles, ditches, and wetlands. The larvae of some species can develop in small containers, including buckets, barrels, tin cans, etc. Decaying organic matter does not harm them. A characteristic feature of Aedes mosquitoes is the asynchronous hatching of larvae from the eggs of a single clutch, which can stretch over weeks or even months. This is an adaptation to life in periodically drying water bodies. If a water body dries up before larval development is complete and they die, then upon reflooding, larvae hatch from the remaining eggs. This ensures the survival of the species. Some Aedes species, referred to as monocyclic, are characterized by the development of a single generation per summer, while others—polycyclic—produce several generations. Adult mosquitoes are most active in the evening, but they can also attack hosts during the day, especially in cloudy weather. During the day, they hide in grass, bushes, and pits near water bodies. Aedes mosquitoes overwinter in the egg stage.

Medical significance: mosquito saliva injected into the skin during blood-feeding causes painful sensations and local inflammation. Anopheles mosquitoes transmit malaria pathogens to humans and serve as intermediate hosts and vectors of filariasis pathogens. Some Aedes species transmit pathogens of tularemia, Japanese encephalitis, lymphocytic choriomeningitis, yellow fever, Dengue fever, and anthrax; some Culex species transmit pathogens of Japanese encephalitis, tularemia, and filariasis.

Prevention and control measures. Personal—protection against mosquito bites. Public—destruction of mosquitoes at all stages of development. Mosquito control includes A number of measures: 1) elimination of small water reservoirs not used by humans; 2) spraying pesticides in water bodies that serve as breeding sites; 3) oiling water bodies to block oxygen access; 4) clearing vegetation from water bodies; 5) land drainage—reclamation; 6) biological control Methods: breeding mosquitofish (Gambusia), which feed on mosquito larvae (however, Gambusia can only live in water temperatures no lower than +5 °C); utilizing natural enemies (e.g., attracting bats), fungal, bacterial, and viral pathogens of mosquitoes; Genetic Methods (releasing sterile males into the wild); 7) zooprophylaxis—when designing settlements, livestock farms are placed between potential mosquito breeding sites and residential buildings, as mosquitoes readily feed on animal blood; 8) destruction of winged forms in overwintering sites (basements, attics, barns) using insecticides. All insecticides must be applied in a way that does not harm wildlife.

Family Psychodidae (Moth flies). Sandflies of the genus Phlebotomus are temporary ectoparasites and specific vectors of pathogens causing leishmaniases and pappataci fever.

Morphology. Small insects with long legs, bright yellow, gray, or brownish in color, with a body length of 1.3-3.5 mm. The body and wings are densely covered with hairs. They attack at night and during twilight. They are found both near human dwellings and in the wild, where they inhabit caves, burrows of rodents, and other animals.

Fig. 95. Sandfly (Phlebotomus pappatasii).

Life cycle. Development occurs with complete metamorphosis. Larvae develop in decaying organic waste and feed on organic matter. Pupae do not feed. Males feed on plant sap, while females suck the blood of humans and animals. Under optimal temperatures, it takes 46 days from egg-laying to adult development. Most females die after each clutch. Winged sandflies stay close to their breeding sites. With the onset of cold weather, sandflies die. Larvae that hatched from eggs laid by females of the last generation overwinter.

Medical significance: numerous sandfly bites are painful, causing severe itching, papule formation on the skin, and burning sensations. People suffer from sleep loss, and sometimes experience fever, febrile states, general malaise, etc.

Sandfly control measures—clearing areas of waste, applying contact insecticides in residential premises, and destroying rodents in their burrows.

Family Muscidae (Houseflies and allies). Within this family, synanthropic flies are of medical importance as mechanical vectors of pathogens (the housefly, the stable fly) and as causative agents of myiasis.

The housefly (Musca domestica) is a mechanical vector of pathogens causing infectious and invasive diseases. The body length of females is 5.8-7.5 mm. Males are slightly smaller. The mouthparts are of the sponging (licking-sucking) type. By secreting abundant saliva containing enzymes, the fly liquefies solid food and sucks it up. The tarsi feature claws and adhesive pads (pulvilli) densely covered with hairs, allowing flies to walk on ceilings and vertical surfaces. The legs are also covered with hairs. On these hairs, the fly can transport pathogens of various infections, helminth eggs, and protozoan cysts. The presence of flies is particularly dangerous in rooms housing patients with tuberculosis, typhoid fever, or dysentery. Up to 6 million bacteria have been found on a fly's body, and up to 28 million in its gut. Outbreaks of intestinal disease epidemics occur during the summer period, when the fly population reaches its peak.

Development occurs with complete metamorphosis. The female lays eggs wherever decaying organic residues are present (manure, human feces, garbage containers, landfills). She lays 100-150 eggs at a time, and there can be 5-6 such clutches. The larva hatches from the egg in 12-36 hours. It is vermiform (worm-like) in shape, white in color, legless, and has a reduced head. Larvae pupate in the soil, burrowing to a depth of more than 30 cm. Pupae are immobile. The development cycle from egg to adult lasts 10-26 days. The fly lives on average for 30-35 days.

Fly control in populated areas includes the following measures: protecting food products from flies; community sanitation and landscaping; implementing sanitary measures that ensure waste collection and timely cleaning of the territory; composting manure; destroying larvae at fly breeding sites with insecticides, and controlling winged flies using mechanical and chemical means.

The stable fly (Stomoxys calcitrans) is a mechanical vector of pathogens causing anthrax and Sepsis. It is widely distributed. In terms of biology and morphology, it is close to the housefly. The body color is gray with dark stripes on the thorax and spots on the abdomen. The proboscis is highly elongated and features plates with chitinous "Teeth" at its tip. By rubbing its proboscis against the skin, the fly scrapes off the epidermis and feeds on blood, simultaneously injecting toxic saliva and causing severe irritation. Both females and males attack primarily animals, but occasionally humans as well. Control measures are the same as for the housefly.

The Wohlfahrtia fly (Wohlfartia magnifica). It is viviparous. Its larvae cause myiasis. The fly is found in the temperate zone and southern Europe. Adult insects inhabit fields and feed on flower nectar. The female deposits larvae (120-150) during flight into open cavities: eyes, Nose, ears, as well as onto wound and ulcer surfaces of mammals, and sometimes humans, especially children sleeping outdoors. The larvae are highly mobile. Using specialized adaptations, they rapidly penetrate deep into tissues, consuming them down to the bone, creating channels, and destroying Blood Vessels.

Clinical manifestations of myiasis include suppuration, bleeding, gangrenous processes, and severe pain. Eye damage can cause blindness. Fatal cases are known. The duration of larval parasitism in animals is up to 3-5 days. They pupate in the soil, burrowing to a depth of up to 32 cm. Control measures against fly larvae are complicated by the fact that they penetrate very deeply into tissues. They are removed surgically with forceps, followed by appropriate wound treatment.

The tsetse fly (Glossina palpalis) is a vector of the causative agent of African trypanosomiasis (sleeping sickness) — the trypanosome (Trypanosoma brucei gambiense). It is viviparous and widespread in West Africa. Its size is 10-13.5 mm, and its lifespan is 3-6 months. During this time, the female deposits a single live larva onto the soil surface 6-12 times. In the soil, the larvae pupate, and adult flies emerge after 3-4 weeks. They mostly inhabit shrubby vegetation along riverbanks and lakeshores, as well as near human dwellings. They feed primarily on human blood, and less frequently on the blood of domestic and wild animals. To control the flies, shrubs and trees are cleared along water bodies, near human habitations, and along roads. Insecticides are also used.

Biting flies (gnus) and their components. The term "gnus" refers to all blood-sucking dipteran insects that attack humans and animals in large numbers (mosquitoes, sandflies, biting midges, blackflies, horseflies, and certain species of biting flies).

Fig. 96. Main Components of the "gnus" complex: 1 — horsefly (Tabanus bromis); 2 — deer fly (Chrуsорs flavipes); 3 — rain-fly (Haematopota pluvialis); 4 — mosquito (Aedes communis); 5 — blackfly (Simulium sp.); 6 — biting midge (Culicoides); 7 — sandfly (Phlebotomus pappatasii).

Breeding sites for these biting insects are primarily floodplains and river deltas, areas of artificial irrigation, rice cultivation, and stagnant water bodies. The species COMPOSITION OF THE complex depends on the landscape and geographical zone. In the Siberian taiga, tundra, and other regions, they appear in massive numbers, attacking animals and humans in swarms and causing severe distress. In some cases, sensitization (hypersensitivity) to subsequent bites occurs, which can lead to severe conditions, including anaphylactic Shock. People are deprived of proper rest, and their productivity decreases. For personal protection, Pavlovsky nets, protective clothing made of special mesh fabric (which prevents the insect's proboscis from reaching the skin), and repellents (such as dimethyl phthalate, etc.) are used.

Family Ceratopogonidae (biting midges). The majority of blood-sucking biting midges belong to the genus Culicoides. These are the smallest of the flying blood-sucking insects, with a body length of 1-2.5 mm. Females attack humans and animals during the morning and evening hours. Larvae and pupae develop in moist soil, forest litter, tree hollows, and small stagnant water bodies. Biting midges are mechanical vectors of the causative agent of tularemia, and in the tropics, they serve as specific vectors and intermediate hosts of nematodes (filariae).

Family Simuliidae (blackflies). In appearance, they resemble small flies, with a body length of 2.5-4.5 mm. Females of most species feed on blood. They attack only outdoors during daylight hours. Development occurs in rivers and streams. Blackflies are mechanical vectors of the causative agent of tularemia, and in the tropics, blackflies of the genus Simulium are specific vectors of filariae (Onchocerca volvulus, O. coecutiens).

Family Tabanidae (horseflies). In appearance and size, they resemble large flies. They have a large head with brightly colored eyes. They undergo complete metamorphosis. Males feed on plant juices. Females also feed on plant juices, but after fertilization, they require a blood meal for egg development. They attack in hot weather and buzz during flight. A horsefly bite is painful; it is also unpleasant because the insect can make 8-10 punctures with its proboscis. The saliva of horseflies is toxic, and blood flows from the wound for a long time because hemolysin is injected. Most species lay eggs on the leaves of riparian vegetation. Horseflies are mechanical vectors of the causative agents of tularemia and anthrax, and deer flies of the genus Chrysops transmit filariae (Loa loa) in Africa.