Specific and non-specific carriers. Classification of natural foci. Mechanical vectors of vector-borne infections

coursework

Biology and genetics

Transmission of the pathogen by the carrier occurs when bloodsucking through the proboscis (inoculation), through contamination of the host's integument with the excrement of the carrier, in which the pathogen is located (contamination), through eggs during sexual reproduction (transovarially).

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

federal state budgetary educational institution

higher professional education

« MOSCOW STATE UNIVERSITY OF FOOD PRODUCTION»

institute of veterinary expertise of sanitation and ecology

Department of Microbiology Virology and Genetic Engineering

course work in biology with the basics of ecology

transmissible diseases. Their focality. measures to combat them.

Completed by: 1st year student

1 group IVESiE

Malchukovskaya Tatyana Igorevna

Checked by: Ph.D., Associate Professor Chulkova N.V.

Moscow 2013

Definition of vector-borne diseases……………………………………………………………………………………………………. 3

Classification of vector-borne diseases……………………….…page 4

………………………………….. page 4

Classification of carriers………………………………………………………….page 5

Specific carriers……………………………………………………………..page 6

Mechanical carriers……………………………………………………………………..page 31

Natural hearth and its structure………………………………………………………….…p.36

and natural focal diseases…………………………………………………… p.38

List of used literature…………………………………………………...page 40

Transmissibleare called diseases, the causative agents of which are transmitted through the blood by a carrier - arthropods (ticks and insects).

Carriers can be mechanical and specific.

Mechanical carriers(flies, cockroaches) carry pathogens on the integument of the body, on the limbs, on parts of the oral apparatus.

In organism specific vectorspathogens go through certain stages of development (malarial plasmodia in a female malarial mosquito, a plague bacillus in a flea organism).

The transmission of the pathogen by the carrier occurs when bloodsucking through the proboscis (inoculation), through contamination of the host's integument with the excrement of the carrier, in which the pathogen is located(contamination), through eggs during sexual reproduction(transovarially).

At obligate-transmissive disease the pathogen is transmitted only by a carrier (example: leishmaniasis).

Optional-transmissible disease (plague, tularemia, anthrax) are transmitted through a vector and in other ways (through the respiratory system, through products of animal origin).

Classification of vector-borne diseases:

1. Obligate - vector-borne diseasestransmitted from one host to another only through a blood-sucking vector (Typhus can only be transmitted to humans through the head louse.).

2. Optional - vector-borne diseasestransmitted as through a carrier, and without it ( the causative agent of plague can be transmitted to humans through flea bites and through the air- drip from a patient with pneumonic plague)

Ways of transmissible transmission of the pathogen:

Inoculation host infection occurs by blood-sucking, the exit gate is the oral apparatus of the carrier. , because the carrier does not die(malaria).

Contamination Human infection occurs when the carrier's feces are rubbed into the bite site., the exit gate is the anus. This transfer happens multiple times., since the carrier does not die (lousy typhus).

Specific contamination – transmission of the pathogen occurs when the carrier is crushed and the contents of the internal environment are rubbed into the bite site, there is no exit gate of the pathogen and it accumulates in the body cavity of the carrier. This transfer occurs only once., as the carrier dies(relapsing fever).

Transovarial transmission – ( characteristic of ticks) the pathogen from the body of the female enters the zygote(egg), then into a larva, nymph and further into imago (taiga tick transmits encephalitis virus in this way)

Carrier classification:

1. Specific in their body, the pathogen goes through certain stages of its development (female mosquito of the genus Anopheles for malarial plasmodia);
2. Mechanical in their body, the pathogen does not pass its development, but only accumulates and moves with the help of a carrier in space(cockroaches).

Specific carriers have pathogen entry and exit gates:

1. Entrance gate mouthparts of the carrier, through which the causative agent of the disease enters the body of a blood-sucking arthropod from the body of a diseased host.
2. Exit gate or oral apparatus, or the anus of the carrier, through which the causative agent of the disease enters the body of a healthy host and infects it.

SPECIFIC TRANSMITTERS

1. Ticks of the genus Ixodes.

Pincer length 110 mm. About 1000 species of ixodid ticks have been described. Fertility up to 10,000, in some species up to 30,000 eggs.

Tick ​​body oval, covered with an elastic cuticle.

Males reach a length of 2.5 mm, their color is brown. The hungry female also has a brown body. As it becomes saturated with blood, the color changes from yellow to reddish. The length of a hungry female is 4 mm, well-fed up to 11 mm in length. On the dorsal side there is a shield, which in males covers the entire dorsal side. In females, larvae and nymphs, the chitinous shield is small and covers only a portion of the anterior part of the back. On the rest of the body, the covers are soft, which makes it possible to significantly increase the volume of the body when absorbing blood. The development cycle is long up to 7 years.

Ixodinae are unable to form a cemented proboscis sheath. Feeding is accompanied by the injection of saliva into the body of the host. The saliva of ixodid ticks has osmoregulatory and immunosuppressive properties. Ixodinae ingest partially hemolyzed blood.

Nutrition is accompanied by a significant increase in body size by the type of neosomia (accumulation of food products in the midgut for 5-6, 9-10 days). Individuals that have completed cavitary digestion enter diapause. In unfertilized females, bloodsucking does not end, complete saturation does not occur.
Ixodid ticks are vectors and reservoirs of pathogens infectious diseases.

Mode of infection Inoculation

tularemia, taiga encephalitis, Scottish encephalitis.

2. Ticks of the genus Dermacentor

The characteristic morphological features of the genus Dermacentor include the presence of light enamel pigments in the form of spots of various shapes and sizes, best expressed on the dorsal shield, and to a lesser extent on the legs and proboscis. The shape of enamel spots and their number vary considerably within one species and even one population.

Entrance gate - oral apparatus

Mode of infection Inoculation

What pathogens does it carry? tularemia, Taiga encephalitis, Tick-borne encephalitis With typhus, brucellosis.

3. Ticks of the genus Hyalomma

Most species are found in steppe-desert and desert landscapes. Some species inhabit enclosed spaces: cattle yards, barns, stalls. H. marginatum Koch - large mites. Development occurs according to a two-host cycle (the development of a larva into a nymph and a nymph into an adult tick occurs on the same host. An adult tick is looking for a new victim.). Imago feeds on large domestic animals during the entire warm period, larvae and nymphs on birds and small mammals. The development cycle lasts 1 year. From eggs laid by females, after 1.5-2 months. larvae hatch. Larvae and nymphs feed on rodents, hedgehogs, ground-feeding birds. Well-fed nymphs molt to adults in the same season. Hungry adults hibernate. Ticks of the genus Hyalomma - actively attacking bloodsuckers. From a distance of several meters, they pursue animals (humans), guided by their sense of smell and vision. After leaving the host, well-fed females crawl into shelters before the onset of heat, leaving a characteristic mark on the sand.The virus is transmitted to ticks by the bite of an infected domestic or wild animal. Babesiosis is also transmitted. Ticks of the genus Hyalomma are distinguished by increased resistance to acaricides.

Bites from Hyalomma mites cause the surrounding tissue to die and become necrotic. Dead tissue will peel off the body after a few days. The wounds look very serious, but usually heal without any intervention and generally do not become infected further.

Entrance gate - Mouth apparatus

Mode of infection Inoculation

What pathogens does it carry? Tularemia, Crimean hemorrhagic fever.

4. Ticks of the family Argasidae

The body has a length of 3 to 30 mm, flattened, oval. The integument is leathery, the color of ticks drunk with blood is lilac, in hungry ticks it is grayish, yellow-borax.The mouth apparatus of argas ticks is located on the ventral side of the body and does not protrude forward. There is no chitinous shield on the dorsal side. Instead, there are numerous chitinous tubercles and outgrowths, so the outer integument of the body is highly extensible. A wide welt runs along the edge of the body. Length of hungry ticks 213 mm.

Entrance gate - Mouth apparatus

Mode of infection Inoculation

What pathogens does it carry? tularemia, tick-borne, relapsing fever

5. Ticks of the family Gamasoidea

The body is oval or oblong (0.34 mm), covered with scutes (solid or double dorsal and several abdominal); body with numerous setae, constant in number and position. The legs are six-segmented, with claws and a sucker. Mouthparts gnawing-sucking or piercing-sucking.

Infection occurs through contact with infected birds and rodents. The disease manifests itself in the form dermatitis accompanied by itching .The mouse tick and the rat tick also attack humans. As a rule, the main bite zones are those places where clothing fits more tightly to the skin: zones of cuffs, elastic bands, belts. At first, a person feels a slight tingling sensation, then a burning sensation and itching. Itchy rashes go on the skin, an inflammatory process begins, which spreads.

Entrance gate - Mouth apparatus

Mode of infection Inoculation

What pathogens does it carry? Tularemia, Rat fever, typhus, Q fever, encephalitis.

6. Human flea(Pulexirritans)

The body color is brown (from light brown to black brown). Life expectancy up to 513 days.

Her body is ovoid; head rounded, without spines on lower margin. The first thoracic ring is very narrow, with an entire margin and also without spines. The hind legs are very strongly developed. The eyes are large and rounded. Length approximately 2.2 mm (male) or 34 mm (female).

Found everywhere. With a length of 1.63.2 mm, they can jump up to 30 cm in height and up to 50 cm in length.

Pulexirritans lives on humans, but can pass on to domestic cats and dogs. It feeds on the blood of humans or animals on which it lives. It can make very large jumps, up to 1 meter in height.

The mouthparts of fleas are adapted for piercing the skin and sucking out blood; the puncture of the skin is carried out by jagged mandibles. Feeding, fleas fill the stomach with blood, which can greatly swell. Male fleas are smaller than females. Fertilized females forcefully eject eggs, usually in batches of several pieces so that the eggs do not remain on the animal's fur, but fall to the ground, usually in the hole of the host animal or in other places it constantly visits. A legless, but very mobile, worm-like larva with a well-developed head emerges from the egg. A human flea lays 7-8 eggs at a time (over 500 eggs in a lifetime) in floor crevices, rags, rat nests, dog kennels, bird nests, soil, plant waste.

Entrance gate - Proboscis, anus.

Mode of infectionInoculation, contamination

Tularemia, Plague

7. Pediculus humanus lice (human lice)

The body is oval or oblong, flattened in the dorsal-abdominal direction, 0.5-6.5 mm long, 0.2-2.5 mm wide, the color is grayish-brown, in individuals fed with fresh blood, it varies from reddish to black in depending on the degree of digestion.

Their body consists of three sections: the head, chest and abdomen. The head is small, tapering anteriorly, has five-membered antennae (antennae), behind them are simple eyes with a transparent cornea, under which accumulations of pigment are visible. The front edge of the head is correctly rounded, with a small mouth opening, the oral apparatus is of a piercing-sucking type, consists of three stylets: the lower one, the top of which is notched, serves to pierce the skin, blood is pumped along the upper zholobovatoy, saliva enters the wound through the tubular middle stylet. salivary gland ducts. At rest, all stylets are hidden inside the head and are not visible from the outside at all. Males are usually smaller than females. Lice are oviparous. Eggs (nits) oblong - oval shape(1.0-1.5 mm in length), covered with a flat lid on top. Nits are yellowish-white in color, glued with the lower end to the hair or villi of the fabric with a secret secreted by the female during laying. Metamorphosis is incomplete, accompanied by three molts. All three larvae (or nymphs) differ from adults in the absence of external genitalia, size, and slightly different body proportions. Nymphs usually have a relatively large head and thorax and a vaguely delimited short abdomen that enlarges after each successive molt. After the 3rd molt, the nymph turns into a male or female, by this time the genitals are formed and the lice are able to copulate. Lice are kept on the hairline near the skin, body lice - mainly on clothes. Infection of people with lice occurs through contact with lice-covered persons, for example, through contact of children in groups (kindergartens, boarding schools, camps, etc.), in crowded transport, when sharing clothes, bedding, bedding, combs, brushes, etc. .d. Infection of adults with pubic lice occurs through intimate contact, and in children - from adults caring for them, as well as through underwear.

Entrance gate - anus

Mode of infection Inoculation

What pathogens does it carry?typhus, relapsing fever.

8. Kissing bug (Triatominae Jeannel)

It has a strongly flattened body with a length of 3 to 8.4 mm, depending on blood saturation. Males are on average smaller than females. Dirty yellow to dark brown coloration. From leading edge head moves away proboscis adapted for puncturing tissues and sucking blood. The upper and lower jaws look like piercing undivided bristles and form two channels: wide for receiving blood and narrow for excretion saliva at the injection site.

Due to the geometry and flexibility of the segmented body, the hungry bug is weakly vulnerable to mechanical methods of dealing with it. A well-fed bug becomes less mobile, its body acquires a more rounded shape and the color corresponding to blood (by the color of which from scarlet to black you can roughly determine when this individual last ate).The average lifespan of bed bugs is one year. Bed bugs can go into a state similar to anabiosis , in the absence of food or low temperatures. In adverse conditions, capable migrate between the rooms ventilation ducts, summer on the outer walls of houses. An adult bug crawls 1.25 m in one minute, a larva up to 25 cm. The bugs have a well-developed sense of smell, they drink blood in all phases of development, in one bloodsucking of 1015 minutes the bug drinks 7 μl of blood, which is equal to its double weight. It usually feeds regularly every 5-10 days, mostly on human blood, but can also attack domestic animals, birds, rats and mice. IN countryside often crawl from infected poultry houses to houses.

Bedbugs are able to survive in a limited temperature range. At a temperature of 50˚С, bedbugs and their eggs die instantly.

mate bedbugs by traumatic insemination. Male pierces his genitals the female's abdomen and injects sperm into the resulting hole. All types of bed bugs except Primicimex cavernis , sperm enters one of the departments of Berlese's organ. Gametes can stay there for a long time, then hemolymph penetrate into the ovarioles to the formed eggs. This method of reproduction increases the chances of survival in case of prolonged starvation, since stored gametes can be phagocytosed. insect withincomplete transformation. Females lay up to 5 eggs per day. In total, during the life of 250 to 500 eggs. Full cycle development from egg to imago is 3040 days. Under adverse conditions 80100 days.

Entrance gate - Anal opening.

Mode of infection Contamination

What pathogens does it carry? American trypanosomiasis.

9. Mosquitoes (Phlebotominae).

Size 1.52 mm, rarely exceeds 3 mm, color varies from almost white to almost black. The legs and proboscis are quite long. Mosquitoes have three distinguishing characteristics: at rest, the wings are raised at an angle above the abdomen, the body is covered with hairs, before biting, the female usually makes several jumps on the host before biting into it. They usually move in short jumps, fly poorly, the flight speed usually does not exceed 1 m / s.

Subfamily of long-whiskered dipterous insects of the gnat complex . Predominantly distributed in tropics and subtropics . Includes several genera notably Phlebotomus and Sergentomyia in the Old World and Lutzomyia in the New World , which includes a total of more than 700 species. Representatives of these genera are important as carriers human and animal diseases.

Mosquitoes live mainly in warm regions, but the northern limit of their range lies just north of 50 ° north latitude in Canada and a little south of the fiftieth parallel in the northern France and Mongolia.

insects , mosquitoes have 4 phases of development:. Mosquitoes usually feed on natural sugars - plant sap, ashes , but females require blood to mature their eggs. The number of blood draws may vary depending on the species. Egg maturation time depends on species, blood digestion rate and temperature environment; under laboratory conditions usually 48 days. Eggs are laid in places favorable for the development of preimaginal stages. The preimaginal stages include an egg, three (or four) larval stages, and a pupa.Mosquito breeding sites have not been studied enough, but it is known that they have larvae, unlike most butterflies , not water, but from observations of laboratory colonies, it can be concluded that the main requirements for the breeding site are humidity, coolness and the presence of organic substances. Most mosquitoes are active intwilight and night time. Unlike mosquitoes they fly silently. The Italian name for the mosquito, which gave the name to the type species "pappa tachi" means "bites silently"

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry? Dermal, skin- mucosal and visceral leishmaniasis, Pappatachi fever.

10. Biting midges (Ceratopogonidae).

Small insects 1 - 2.5 mm long. They are the smallest of the blood-sucking Diptera. They differ from midges in a more slender body and longer legs; antennae consist of 13 or 14 segments, and palps - of 5 segments; on the third, thickened, are the sense organs. The mouth apparatus is of a piercing-sucking type, the length of the proboscis is almost equal to the length of the head. Wings are usually spotted.

Family very small (the largest species in the world do not exceed 4 mm, the vast majority are less than 1 mm) Diptera long-whiskered suborder, females imago which in most cases are a component of the complex vile.

Like all other Diptera insects , biting midges have 4 phases of development: egg, larva, pupa, adults saprophages or nectar predators flowering plants.

The larvae of biting midges are worm-like, with a well-defined sclerotized head capsule and a body consisting of 3 thoracic and 9 abdominal segments, outwardly little different from each other, and a differently expressed cervical segment - the neck, the body is devoid of appendages. Some species lay up to 20,000 eggs. The larvae of some species of biting midges live in water, while others live in wet places on land, in forest litter, hollows, under bark, and even in garbage. Their breeding grounds are very diverse. These are reservoirs, floodplains of lakes, channels, temporary streams, puddles in water meadows, small rivers with a slow flow of water, backwaters, swamps without hummocks with a clay bottom, temporary reservoirs near taiga villages, puddles near wells, on livestock farms. Some species live in the brackish water of salt lakes, in the bays of the Aral Sea, etc..The maximum activity occurs in the early morning and evening. Active season in middle lane Russia lasts from May to September, in the south - from April to October - November. Optimum activity is observed at a temperature of 13 - 23°C.

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry? Onchocerciasis, eastern encephalomyelitis horses, blue tongue disease sheep, livestock filariasis and humans, their bites can cause an allergic reaction.

12. MuhaTse - Tse (Glossinapalpalis)

The body length is 9-14 mm, there is an expressive proboscis, an oblong shape attached to the bottom of the head and directed forward. At rest tsetse adds up wings completely, laying one wing on top of the other, in the middle part of the wing, a characteristic segment in the form of an ax is clearly visible. The antennae of the tsetse fly have awns with hairs that branch out at the ends.

T type genus of insects from the family of flies Glossinidae, live in tropical and subtropical Africa.

Tsetse flies can be distinguished from common ones in Europe house flies by the nature of the folding of the wings (their ends lie flat on each other) and by the strong piercing proboscis protruding on the front of the head. The chest of the fly is reddish-gray with four dark brown longitudinal stripes, and the abdomen is yellow above and gray below.

The usual food source for tsetse flies is the blood of large wild mammals.

All tsetse species are viviparous, larvae are born ready to pupate. The female bears the larvae for a week or two, at one time she lays a fully developed larva on the ground, which burrows and immediately pupates. By this time the fly is hiding in shady place. A fly gives birth to larvae 810 times in its life.

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry?African trypanosomiasis (sleeping sickness)

13. Horseflies (Tabanidae).

Large flies (body length 630 mm), with a fleshy proboscis , inside which are enclosed hard and sharp piercing and cutting stilettos; palps clear, with swollen end segment hanging in front of proboscis; antennae 4-segmented, projecting forward; wing scales well developed in front of halteres; the eyes are huge, with stripes and spots of iridescent colors; mouthparts are made up of mandible, jaws, upper lip and subglottis; lower lip with wide lobes. Horseflies are observedsexual dimorphismby appearance males can be distinguished from females. In females, the eyes are separated by a frontal stripe, in males distance between eyes almost imperceptible and abdomen pointed at the end.

Horseflies inhabit everything continents except Antarctica . Moreover, they are absent in Iceland, Greenland and on some oceanic islands. The largest number horseflies both in number and number of species (up to 20 in each locality), found in wetlands, on the borders of different ecotopes , in grazing areas livestock. From the neighborhood of man their number is only increasing.

Like all other Diptera insects , horseflies have 4 phases of development: egg, larva, pupa, adult . Horsefly larvae predators or saprophages feed on water and soilinvertebrates. The nutrition of adults is dual: females of most species of horseflies drink blood warm-blooded animals: mammals and birds ; at the same time, males, of all horsefly species without exception, feed nectar flowering plants. Imagoes fly, spending most of their time in the air, orienting themselves mainly with the help of vision . Active during the day in warm weather solar time. Horsefly females lay eggs in large groups of 5001000 pieces. Eggs horseflies have elongated, gray, brown or black. Larvae most often light fusiform, devoid of limbs. pupae slightly reminiscent of a chrysalis butterflies.

Horsefly eggs are attached to plants near water and above water. Egg laying with a dense, shiny shell. The hatched larvae immediately fall into the water and live at the bottom in the silt. The larvae are white, their body is covered with motor tubercles, the head is very small. They develop in or near water, in damp soil, under stones. They feed on organic remains, plant roots, some species attack insect larvae, crustaceans, earthworms.

On hot days, herds of animals are attacked by tens of thousands of horseflies. They are especially abundant in places with ponds and thickets of plants.

Only female adult horseflies bite cattle and drink blood, each of which can suck up to 20 mg of blood at a time. Only after that she is able to lay eggs. Horseflies from time to time fly to the reservoir and capture a drop of water from the surface. Males feed on the nectar of flowers. With their bites, horseflies exhaust animals, reducing their productivity, and greatly annoy people.

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry? Loaoz , anthrax, tularemia, trypanosomiasis, filariasis.

14. Mosquitoes of the genus Aedes.

The length is from 2 to 10 mm and has a black and white color in the form of stripes and spots.

The male is 20% smaller than the female, but their morphology is similar. However, like all blood-sucking mosquitoes, the antennae of males, unlike females, are elongated and thick. The antennae also serve as an auditory receptor, with which he can hear the squeak of the female.

An adult develops from an egg within 6-8 weeks. In its development, the biter goes through all stages of development: egg larva pupa adult insect. Eggs are white or yellowish during laying, but quickly turn brown. Females either lay them one at a time or stick them together in "rafts" that include from 25 to several hundred eggs.The larvae live in the water and feed on dead plant tissue, algae and microorganisms, although predators are also known to attack the larvae of other mosquito species. The pupae are similar to tadpoles and swim due to the bending of the abdomen. In the end, the pupa floats to the surface, the dorsal integument of its chest bursts, and an adult mosquito emerges from under them. For some time, until the wings are straightened, he sits on the shell of the pupa, and then flies away to the shelter, which he finds not far from the breeding site, where the final hardening of his covers takes place.

The mosquito bites most actively at dusk and dawn, but also during the daytime in residential areas or in cloudy weather. In clear sunny weather, they hide in the shade.

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry? dengue fever, chikungun ya, yellow fever, wuchereriosis , brugioz .

15. Mosquitoes of the genus A nopheles.

Slender Diptera with an elongated body, small head, long thin proboscis, mostly with long legs. The wings, covered with scales along the veins, at rest fold horizontally over the abdomen, leaning one on top of the other. The body is fragile mechanical strength is not different.

Widely distributed on all continents except Antarctica] . Absent in desert areas and in the far north (extreme north point range south of Karelia). There are about 430 species in the world fauna, 10 species in Russia and neighboring countries. In Russia, they live in the European part and Siberia
.

Mosquito larvae have a well-developed head with mouth brushes used for feeding, big breasts and segmented abdomen. Legs are missing. Compared to other mosquitoes, malarial mosquito larvae lack a respiratory siphon and therefore the larvae keep themselves in the water parallel to the water surface. They breathe with the help of spiracles located on the eighth abdominal segment and therefore must periodically return to the surface of the water to inhale air.

Pupae in the form of a comma, when viewed from the side. The head and thorax are fused into the cephalothorax. Like larvae, pupae must periodically rise to the surface of the water to inhale, but inhalation is done using breathing tubes on the cephalothorax.

Like other mosquitoes, malaria go through all the same stages of development: egg, larva, pupa and adult. First three stages develop in the water of various reservoirs and last a total of 5-14 days, depending on the type and ambient temperature. The lifespan of adults is up to a month in the natural environment, in captivity even more, but in nature it often does not exceed one to two weeks. females different types lay 50200 eggs. Eggs are placed one at a time on the surface of the water. They tend to float upward on either side. Not drought tolerant. The larvae appear within two to three days, but hatching may be delayed up to two to three weeks in colder areas. The development of larvae consists of four stages, or instars, at the end of which they turn into pupae. At the end of each stage, the larva molts in order to increase in size. At the end of development in the pupal stage, the cephalothorax cracks and separates and an adult mosquito emerges from it.

A mosquito becomes infected with malarial plasmodium from a person sick or carrier. The malarial Plasmodium goes through a cycle of sexual reproduction in the body of the mosquito. An infected mosquito becomes a source of infection for humans 4-10 days after infection and remains so for 16-45 days. Mosquitoes serve as carriers of other types of Plasmodium that cause malaria in animals.

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry? Malaria

16. Mosquitoes of the genus C u lex.

An adult mosquito reaches 410 mm in length. Has the usual insect body structure: head, thorax and abdomen, having a proboscis with dark bristly and dark short palps . Wings 3.54 mm long with narrow black brushes. The male, unlike the female, has a fluffy antennae.

Females feed on plant sap (to maintain life) and blood (to develop eggs), mainly of humans, while the male feeds exclusively on plant sap..

From the eggs laid by the female common mosquito, develop larvae , which, after four stages of metamorphosis, separated by three molting , molt for the fourth time, turning into pupae , and from them, in turn, mature mosquitoes (adults) come out.

Larva characterized by a relatively short siphon bearing a comb of 1215 teeth. The siphon does not expand at the end, its length is not more than six times the width at the base. There are four pairs of siphon bundles, the length of which slightly exceeds or does not exceed the diameter of the siphon at the point of their attachment. The pair closest to the base of the siphon lies at an appreciable distance closer to the apex from the most distal tooth of the ridge. Lateral hair on last segment usually simple.

The siphon is located on the eighth segment of the abdomen and serves to breathe air. At the end of the siphon there are valves that close when the larva is immersed deep in the water. The larva moves thanks to the caudal fin on the last, ninth segment of the abdomen, consisting of bristles.

chrysalis The common mosquito is outwardly very different from the larva. She has a large transparent cephalothorax , through which the body of the future mature mosquito is visible. From pupaemalarial mosquitodiffers in that two breathing tubes extending from the cephalothorax, with which the pupa is attached to the surface of the water and breathes air, have the same cross section throughout; in addition, it has no spines on the abdominal segments. The abdomen consists of nine segments, the eighth of which has a caudal fin in the form of two plates. Moves due to the movements of the abdomen. The duration of the stage is a couple of days.

The female lays her eggs in warm stagnant water with organic materials or aquatic vegetation. Eggs are laid in the form of rafts that float freely in the pond. In one raft there may be 20 to 30 eggs stuck together. The duration of development is from 40 hours to 8 days, it depends on the temperature of the water in which development occurs.

Deep terrain or waves are detrimental to mosquito larvae.

Often the habitat of the common mosquito is an urban area. With the onset of cold weather, mosquitoes often fly into the basements of residential buildings, where, at room temperature and the presence of stagnant water, favorable conditions are created for their reproduction and the subsequent development of larvae and pupae. Mature mosquitoes from basements enter the apartments of residential buildings, this can often happen in winter.

Entrance gate - Hobotok.

Mode of infection Inoculation.

What pathogens does it carry? Wuchereriosis, brugiasis, Japanese encephalitis.

MECHANICAL CARRIERS

1. Cockroaches (Blattoptera, or Blattodea).

The body is flattened, oblong-oval in shape, in a red cockroach up to 13 mm long, in a black one up to 30 mm. Mouth apparatus gnawing type. Antennae long, consisting of 75-90 segments. There is a pair of compound eyes and a pair of simple eyes. The legs are running, ending in two claws and suckers between them. The wings are delicate, transparent, at rest hidden under the elytra. The abdomen is flat, consisting of 8-10 tergites and 7-9 sternites. Leads a predominantly nocturnal lifestyle.

It is characterized by an incomplete development cycle. Imago reach a length of 10-16 mm and are painted in various shades of brown with two dark stripes on the dorsal side prothorax . It has developed wings and is capable of short flight (planning). Male individuals have a narrower body, edge abdomen wedge-shaped, its last segments are not covered by wings. In females, the body is wide, the edge of the abdomen is rounded and covered from above by wings.Females lay 30-40 eggs in ootheca brown capsule up to 8x3x2 mm. Cockroaches often wear ootheca until after 14-35 days the eggs hatch. nymphs , which differ from adults only in the absence of wings and usually darker coloration. The number of links through which the nymph turns into an adult varies, however, usually equals six. The time it takes for this to happen is about 60 days.

The life span of adults is 20-30 weeks. One female can produce from four to nine ootheca in her life.

Cockroaches, having contact both with garbage, dirt accumulated in the cracks, garbage, and with fresh human food, can cause the spread of various diseases.

What pathogens does it carry? Protozoan cysts, helminth eggs; viruses, bacteria causative agents of dysentery, typhoid, paratyphoid, tuberculosis, etc. d .

2. Houseflies(Muscadomestica).

The body is dark, sometimes yellow, also sometimes with a metallic sheen (blue or green), body length 7-9 mm. From above, the body is covered with hairs and setae, from 2 to 20 mm long. Members of the family have a single pair of membranous wings and a pair of halteres transformed from the hindwings. The head is quite large, mobile, while the mouth apparatus in the form of a proboscis is adapted for sucking or licking liquid food.

Family of short-winged Diptera insects, which includes about five thousand species, divided into more than a hundred genera.

The larvae are white, worm-like, legless, do not have a separate head and are dressed in a thin transparent shell. At the end of their development, the larvae pupate, for which they crawl to drier and cooler places. The pupa is in an oval-cylindrical brown cocoon. The duration of development depends on temperature and averages 10-15 days. A fly emerging from a chrysalis cannot fly for the first two hours of its life. She crawls until her wings dry and harden. Adult flies feed on a wide variety of solid and liquid substances of plant and animal origin.

What pathogens does it carry?Protozoan cysts, I helminth eggs ; viruses, bacteria causative agents of dysentery, typhoid, paratyphoid, tuberculosis, etc. e.)

3. Autumn burner(Stomoxys calcitrans).

Length 5.57 mm. It has a gray color with dark stripes on the chest and spots on the abdomen. Proboscis strongly elongated and at the end bears plates with chitinous "teeth".

By rubbing the proboscis against the skin, the fly scrapes epidermis and, feeding on blood , simultaneously admits poisonous saliva, causing severe irritation. Females and males feed on blood, attacking mainly animals, but sometimes humans. Fertility 300400 eggs, laid in groups of 2025 in manure, less often on rotting plant residues, sometimes in animal and human wounds, where the larvae develop.. Eggs and larvae develop at a temperature not higher than 30-35⁰С. The larvae pupate in a dry substrate. The larvae and adults in the state of diapause overwinter in cold stables.

What pathogens does it carry? anthrax, tularemia, trypanosomiasis

4. Midges (Simuliidae).

Adult midges range in size from 1.5 to 6 mm.

Females lay their eggs in streams and rivers with fast-flowing water, gluing them to stones and leaves submerged in water. The development cycle of insects is from 10 to 40 days. , and in the case of wintering up to 10 months. They attack during daylight hours, in the northern latitudes during the polar day - around the clock (sometimes up to several thousand individuals per person at the same time). Insect saliva contains a strong hemolytic poison.

Like all other dipteran insects, midges have 4 phases of development: egg, larva, pupa, imago. At the same time, all phases, except adults, live in water bodies, mostly flowing (streams and rivers with fast-flowing fresh water).

Midge eggs are laid on constantly wetted stones, leaves and other objects. Females of some species, when laying eggs, descend along the substrate under water, while others drop eggs into the water in flight, which immediately sink. The eggs of midges are round-triangular in shape. Freshly laid eggs are white, but as the embryo matures, they darken to brown or black. Midges are characterized by the desire of females of one species to lay eggs one near the other. With joint egg-laying, dozens, and sometimes millions of individuals accumulate in one place, and the laid eggs cover dozens square meters substrate surface. When eggs dry or freeze in ice, the embryos die. The development of eggs lasts 4 15 days, depending on the temperature of the environment. In the case of wintering, their development and hatching of larvae can be delayed by 8 10 months.

When attacked, the midge bites the flesh, while mosquitoes pierce the skin with thin stylet-like mouthparts.

What pathogens does it carry? Tularemia, anthrax, leprosy, leukocytosis birds, livestock onchocerciasis and human, allergic reactions.

5. Biting lice (Ceratopogonidae).

Small insects 1 - 2.5 mm long. They differ from midges in a more slender body and longer legs; antennae consist of 13 or 14 segments, and palps - of 5 segments; on the third, thickened, are the sense organs. The mouth apparatus is of a piercing-sucking type, the length of the proboscis is almost equal to the length of the head. The wings are usually spotted.

Some species lay up to 20,000 eggs. The larvae of some species of biting midges live in water, while others live in wet places on land, in forest litter, hollows, under bark, and even in garbage. Their breeding grounds are very diverse.

Biting midges have 4 phases of development: egg, larva, pupa, adult . At the same time, all phases, except adults, live in water bodies or are semi-aquatic-semi-soil inhabitants. Biting larvae saprophages or predators feed on aquatic and soil organisms or their remains. The diet of adults is varied. Representatives different kinds families can be saprophages, phytophages, predators , as well as their nutrition can be dual: female midges drink blood of mammals, birds or reptiles ; at the same time, both males and females feed nectar flowering plants.

Larvae (up to 15 mm) swim serpentine in water. The entire development cycle of biting biting (at a temperature of 24 - 26 ° C) lasts an average of 30 - 60 days. During the life of the female can do several cycles. Female midges attack animals and people, usually in open area occasionally indoors. The maximum activity occurs in the early morning and evening. Optimum activity is observed at a temperature of 13 - 23°C.

What pathogens does it carry?eastern encephalomyelitis horses, blue tongue disease sheep, livestock filariasis and humans, tularemia.

Natural hearth and its structure

natural hearth - this is a certain geographical landscape in which the pathogen circulates from the donor to the recipient through the carrier.

Donors of the pathogen - they are sick animals

Pathogen recipients - healthy animals that become donors after infection.

The natural focus includes the following components:

1. the causative agent of the disease;
2. pathogen carrier;
3. pathogen donor;
4. pathogen recipient;
5. certain biotope.

End result (outcome) of infectionof a recipient in a natural focus depends on the degree of pathogenicity of the pathogen, on the frequency of the “attack” of the carrier on the recipient, on the dose of the pathogen, and on the degree of preliminary vaccination.

Natural foci are classified by origin and by extent (by area):

By origin, foci can be:

1. natural (foci of leishmaniasis and trichinosis);
2. synanthropic (center of trichinosis);
3. anthropurgic (center of western tick-borne encephalitis in Belarus);
4. mixed (combined foci of trichinosis - natural + synanthropic).

Foci by length:

1. narrowly limited(the pathogen is found in a bird's nest or in a rodent hole);
2. diffuse (the whole taiga can be a focus of tick-borne encephalitis);
3. conjugate (components of plague and tularemia foci are found in one biotope)

Biological basis for the prevention of transmissible

and natural focal diseases.

Blood-sucking arthropods cause significant harm to human health, take a huge number of lives. In the words of academician E.N. Pavlovsky, “proboscis of mosquitoes, lice, fleas killed more people than they died in the battles that ever took place.” Agriculture also suffers significant damage from them.

Great importance has the development and implementation of measures to combat blood-sucking arthropods.

1. Biological control measures: using their natural
   "enemies". For example: a gambusia fish is bred, which feeds on the larvae of a malarial mosquito.
2. Chemical control measures: the use of insecticides (against flies, cockroaches, fleas); processing of places where mosquitoes and small bloodsuckers hibernate (basements, sheds, attics); closed waste bins, toilets, manure storages, waste disposal (against flies); spraying pesticides in water bodies if they are of no economic value (against mosquitoes); deratization (against ticks and fleas).
3. Individual Measures protectionfrom blood-sucking arthropods:

protective liquids, ointments, special closed clothing,repellent, caricidal-repellent and acaricidal agents (chemicals that have the ability to repel living organisms). The protective effect against ticks of all acaricidal and acaricidal-repellent agents, as a rule, is 100%. Therefore, the label must contain the phrase "Violation of the rules of behavior and the method of using the product can lead to the suction of ticks. Be careful!"

Bibliography

1

Arthropods may be specific And non-specific(mechanical) carriers of pathogens of infectious diseases, as well as they themselves cause human diseases (dermatitis, allergies, etc.).

Specific carriers are characterized by the fact that in their body the pathogen goes through a certain development cycle and multiplies or only multiplies. The transfer of the pathogen by a specific carrier to a healthy organism is not possible immediately, but after a certain period of time, during which the pathogen develops and multiplies in the carrier. After a person is bitten by a specific vector, there is an incubation period before the onset of the disease.

In non-specific or mechanical vectors, pathogens can be in the intestines, salivary glands, or on the integument. Upon contact with these arthropods or their secretions, the disease develops rapidly and, as a rule, there is no incubation period. One and the same carrier can be specific, like malarial mosquitoes that carry malaria plasmodia, and at the same time mechanically transmit pathogens of viral infections and tularemia.

The Order of the Ministry of Health of Russia No. 293 of July 2, 1999 contains a list of diseases that require measures for the sanitary protection of territories, which mentions such infections as plague, malaria and yellow fever, the pathogens of which are carried by insect-specific vectors. Decree of the Government of Russia No. 715 of December 1, 2004 “On approval of the list of socially significant diseases and the list of diseases that pose a danger to others” lists viral fevers transmitted by arthropods, malaria, pediculosis, acaridosis, cholera and plague, the pathogens of which can be carried both specific and non-specific carriers.

• smallpox; poliomyelitis caused by wild poliovirus;
• human influenza caused by a new virus subtype J 10, J 114;
• severe acute respiratory syndrome (SARS);
• cholera;
• plague;
• yellow fever, Lassa fever;
• viral hemorrhagic fevers Marburg and Ebola;
• malaria;
• West Nile fever;
• Crimean hemorrhagic fever;
• dengue fever;
• fever of the Rift Valley (Rift Valley);
• meningococcal disease;
• anthrax, brucellosis, tuberculosis, glanders, melioidosis;
• epidemic typhus;
• fever Junin, Machupo;
• other infectious diseases causing in accordance with Annex No. 2 of the International Health Regulations (2005) emergencies in the field of public health. Infections associated with arthropod vectors of infectious diseases are underlined in the List.

Infectious incidence in Russia in 2007-2014 (number of cases)

Table 1

Note: * - data for the period January-September 2014

The concept of vector-borne diseases

Zoonoses are diseases that are transmitted from animal to animal. Humans can also become infected from animals (example: plague of birds and mammals).

Anthroponoses are diseases whose pathogens are transmitted only from person to person (measles, scarlet fever).

Transmissible are called diseases, the causative agents of which are transmitted through the blood by a carrier - arthropods (ticks and insects).

Carriers can be mechanical and specific.

Mechanical carriers (flies, cockroaches) carry pathogens on the integument of the body, on the limbs, on parts of the oral apparatus.

In the body of specific carriers, pathogens go through certain stages of development (malarial plasmodia in a female malarial mosquito, a plague bacillus in a flea body). The transmission of the pathogen by the carrier occurs when bloodsucking through the proboscis (inoculation), through contamination of the host's integument with the excrement of the carrier, in which the pathogen is located ( contamination), through eggs during sexual reproduction ( transovarially).

At obligate vector-borne disease the pathogen is transmitted only by a carrier (example: leishmaniasis).

Optional-transmissible diseases (plague, tularemia, anthrax) are transmitted through a carrier and in other ways (through the respiratory system, through animal products).

Transmissible disease is characterized by the presence of:

Natural hearth and its structure

A natural focus is a specific geographical landscape in which the pathogen circulates from a donor to a recipient through a carrier.

Donors pathogen are sick animals recipients pathogen- healthy animals that become donors after infection.

Scheme of the natural focus of the plague

The natural focus includes the following components:

1. the causative agent of the disease;
2. carrier of the pathogen;
3. pathogen donor;
4. pathogen recipient;
5. certain biotope.

End result (outcome) of infection of the recipient in the natural focus depends on the degree of pathogenicity of the pathogen, on the frequency of the “attack” of the carrier on the recipient, on the dose of the pathogen, and on the degree of preliminary vaccination.

Natural foci are classified by origin and by extent (by area):

By origin, foci can be:

• natural (foci of leishmaniasis and trichinosis);
• synanthropic (center of trichinosis);
• anthropurgic (center of western tick-borne encephalitis in Belarus); mixed (combined foci of trichinosis - natural + synanthropic).

Foci by length:

• narrowly limited (the pathogen is found in a bird's nest or in a rodent's hole);
• diffuse (the whole taiga can be a focus of tick-borne encephalitis);
• conjugated (components of plague and tularemia foci are found in one biotope).

medical significance arthropods

1. Carriers of pathogens (mechanical and specific).
2. Causative agents of diseases (scabies mite, lice)
3. Intermediate hosts of helminths (dipterous insects - for filariae, fleas - for some tapeworms).
4. Poisonous animals (spider scorpions, wasps, bees).

Arthropods as components of natural foci

Order Acari - ticks Family Ixodidae - Ixodes ticks

Representatives: Ixodesricinus - dog tick, Ixodes persulcatus - taiga tick, Dermacentor pictus, Dermacentor marginatus.

The body sizes of ixodid ticks are from 5 to 25 mm. They live on open spaces(in forests). The body has no divisions. Walking limbs - 4 pairs. The first two pairs of limbs form the oral apparatus - the "head". On the dorsal side there is a chitinous shield, which covers the entire dorsal part of the male, and only the anterior part of the females. In ticks of the genus Ixodes, the shield is dark brown; in ticks of the genus Dermacentor, it has a marbled pattern. The "head" is visible from the dorsal side. There are eyes.

Ticks of the family Ixodidae

Features of biology. Blood sucking lasts up to several days. Able to starve up to 3 years. "Bite" ticks are painless, as saliva contains anesthetic substances. The female lays up to 17,000 eggs.

Development stages:

egg → six-legged larva (no stigmas, trachea and genital opening) → several stages of nymphs (underdeveloped reproductive system) → imago.

At each stage, bloodsucking occurs, so the development cycle is called gonotrophic.

Medical significance: they are specific carriers of pathogens of spring-summer and taiga encephalitis. The encephalitis virus infects the salivary glands and gonads of ticks; transmission of the pathogen is possible by blood sucking (inoculation) and through eggs (transovarially). Goats are susceptible to encephalitis, so transmission of the virus through goat milk. Encephalitis virus reservoirs are birds, wild rodents. Ixodid ticks carry hemorrhagic fevers (damage to the walls of blood vessels, kidneys, blood coagulation system), brucellosis, tick-borne typhus, support foci of plague and tularemia. Ticks of the genus Dermacentor carry the causative agent of Scots encephalitis (viral sheep roll), which affects the cerebellum; also occurs in humans.

Family Argasidae - argas mites

Representative: Ornithodorus papillipes - village mite. The size of the tick body is from 2 to 30 mm. The chitinous shield is absent.

The "head" is not visible from the dorsal side. There is an edge welt. The organs of vision are absent.

Ticks of the family Argasidae

Argas mites are shelter forms (caves, rodent burrows, abandoned human buildings). Habitats - zone of steppes, forest-steppes, semi-deserts.

Features of biology: bloodsucking lasts up to 50 minutes. They can starve up to 12-15 years. Oviposition contains 50-200 eggs. Transovarial transmission of pathogens is possible.

Medical significance: specific carriers of tick-borne relapsing fever (tick-borne spirochetosis). Natural reservoirs of the pathogen are cats, dogs, wild rodents. Incubation period disease is 6-8 days. The saliva of ticks is toxic, and persistent ulcers form at the site of the bite. Tick ​​bites can cause death in lambs and sheep.

Family Gamasidae - gamasid mites

Representative: Dermanyssus gallinae - chicken mite.

Order Anoplura - lice

Representatives: Pediculus humanus - human louse.

The P.humanus species has two subspecies: P.humanus capitis - the human head louse and P.humanus humanus - the human body louse.

Lice eggs are called nits. The head louse sticks them to the hair with a sticky secret, the body louse sticks them to the villi of clothes. Development with incomplete metamorphosis. The larva is similar to the adult. The life span of head lice is up to 38 days, body lice - up to 48 days. Head lice and body lice are specific carriers of typhus and relapsing fever (lousy typhus). Human susceptibility to lousy typhus is absolute.

Head and clothes louse

The causative agent of relapsing fever - Obermeyer's spirochete - with the blood of a patient from the louse's stomach penetrates into the body cavity. Human infection occurs when the louse is crushed and its hemolymph is rubbed into the skin during scratching (specific contamination). Immunity after the disease is not produced and relapses of the disease are possible.

The disease caused by lice of the genus Pediculus is called pediculosis (or "tramp disease"). The saliva of lice causes itching, in especially sensitive people - an increase in body temperature. Pediculosis is characterized by pigmentation and coarsening of the skin. Complications of pediculosis - eczema, conjunctivitis, mats (lesion of the scalp).

Order Aphaniptera - fleas

Representatives: fleas of the genus Oropsylla and Xenopsylla (rat fleas) Pulex irritans - human flea

Human flea (Pulex irritans)

Development proceeds with complete metamorphosis. The larvae develop in floor crevices, in dusty corners. Development period - 19 days.

Rat fleas are specific carriers of plague, they carry tularemia, rat typhus. Fleas are intermediate hosts for rat and dog tapeworms. Plague foci persist in India, Pakistan and Burma. Natural foci of plague are maintained by wild rodents. Human susceptibility to plague is absolute. Natural reservoirs of plague are various wild rodents - rats, ground squirrels, marmots, etc. The plague bacillus multiplies in the flea's stomach, forming a "plague block" that closes its lumen. Blood burps when bloodsucking into the wound along with bacteria.

Order Diptera - Diptera.

The front pair of wings are membranous, transparent, the second pair has turned into small appendages - halteres - a flight control organ. On the head are large compound eyes. The mouthparts are licking, sucking, or piercing-sucking.

Family Muscidae - flies

Stomoxys calcitrans is an autumn sturgeon.

Autumn Stinger and Tse-Tse Fly

With chitinous teeth, the proboscis scrapes the epidermis and licks the blood. Her saliva contains toxic substances and causes severe irritation. Zhigalki bites are painful. Its greatest number is in August-September. Autumn Zhigalka carries pathogens of anthrax, tularemia, staphylococcal infections.

Glossina palpalis – tse-tse fly- a specific carrier of sleeping sickness trypanosomes. It feeds on the blood of humans and animals. Viviparous. Body sizes up to 13 mm. Found only in western Africa.

Family Tabanidae - horseflies.

Large flies (up to 3 cm). Males feed on plant juices, females - on the blood of humans and animals. The saliva is poisonous and a swelling forms at the site of the bite. Development with metamorphosis takes place at the bottom of a reservoir or in moist soil. Horseflies are mechanical carriers of pathogens of tularemia and anthrax, intermediate hosts and specific carriers of loiasis.

Midge (Simuliidae)

Family Ceratopogonidae - biting midges.

Body dimensions 1-2.5 mm.

The females feed on blood. Development takes place in moist soil and small stagnant water bodies. Biting midges carry tularemia and some pathogens of filariasis. Involved in the transmission of Japanese encephalitis virus.

Mosquito (Phlebotomidae)

Family Culicidae - mosquitoes.

Mosquitoes (Culicidae)

A - r. Anopheles, B - r. Culex

Mosquitoes r. Culex carry encephalitis, Japanese tularemia, wuchereriosis; mosquitoes of the genus Aedes - tularemia, yellow fever, dengue fever, Japanese encephalitis, anthrax, wuhereriosis. Mosquito bites are painful and cause severe itching.

Biological basis for the prevention of transmissible and natural focal diseases

Blood-sucking arthropods cause significant harm to human health, take a huge number of lives. According to Academician E.N. Pavlovsky "the proboscis of mosquitoes, lice, fleas killed more people than they died in the battles that ever took place." Agriculture also suffers significant damage from them.

Of great importance is the development and implementation of measures to combat blood-sucking arthropods.

A. Biological control measures: the use of their natural "enemies". For example: a gambusia fish is bred, which feeds on the larvae of a malarial mosquito.

B. Chemical control measures: use of insecticides (against flies, cockroaches, fleas); processing of places where mosquitoes and small bloodsuckers hibernate (basements, sheds, attics); closed waste bins, toilets, manure storages, waste disposal (against flies); spraying pesticides in water bodies if they are of no economic value (against mosquitoes); deratization (against ticks and fleas).

B. Individual protection measures against blood-sucking arthropods: protective liquids, ointments, special closed clothing; cleanliness in the premises, wet cleaning; notching the windows of residential premises; cleanliness of the body and clothes.

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The best known are the human flea Pulex imtans and the rat flea Xenopsylla cheopis fig. 21.11, A, B. Both species prefer to feed on the blood of humans and rats, respectively, but also easily pass to other animal species. The rat flea lives in the burrows of rats, and the human flea lives in floor cracks, behind baseboards and wallpaper. Here, the females lay their eggs, which develop into worm-like larvae that feed on decaying organic matter, including the feces of adult fleas. After 3-4 weeks, they pupate and turn into sexually mature insects.

Human fleas visit at night. Their bites are painful and cause severe itching. But the main significance of fleas is that they are carriers of bacteria - the causative agents of the plague. Plague bacteria, having got into the stomach of a flea, multiply there so intensively that they completely close its lumen. This state is called the plague block. 21.11, V. If a flea begins to feed on a healthy animal or person, it, having pierced the skin, first of all regurgitates a bacterial lump into the wound, due to which a huge number of pathogens immediately enter the bloodstream.

The natural reservoir of plague is rodents - rats, ground squirrels, marmots, etc. These animals suffer from a number of other infectious diseases: tularemia, rat typhus, etc. Therefore, fleas are known as carriers of pathogens and these natural focal diseases. Interestingly, in addition to the transmissible method of infection with these diseases, there are other ways: by contact with infected animals, by drinking water from open reservoirs, etc., but with a flea bite, infection is the most likely, and the clinical picture is the most severe.

Flea control - keeping living quarters and outbuildings clean, applying insecticides and various means rodent control.

Give effect and measures personal protection, such as repellents that are used on clothing and bedding.

Mosquitoes. Systematic position, structure, cycle of development. Medical significance of mosquitoes as specific and non-specific carriers of human diseases, control measures.

Mosquitoes lay their eggs in water or on moist soil near water. Larvae and pupae lead an aquatic lifestyle, and breathe atmospheric air with the help of tracheae. The larvae feed on the smallest organic particles suspended in water. The most famous mosquitoes from the genera Culex and Aedes are non-malarial mosquitoes - carriers of pathogens of Japanese encephalitis, anthrax, yellow fever, as well as Anopheles malarial mosquitoes - specific carriers of malarial plasmodium. It has been proven that the susceptibility of mosquitoes to infection with malaria pathogens is determined genotypically and is inherited monogenously. Malarial and non-malarial mosquitoes are easily distinguished from each other at all stages of their life cycle Eggs of malarial mosquitoes Anopheles are found singly on the surface of the water, and each is equipped with two air floats. Their larvae swim in a horizontal position under the surface of the water, and on the penultimate segment they have a pair of breathing holes. The pupae resemble commas in shape, they are, like the larvae, under the water surface and breathe air oxygen through breathing horns shaped like wide funnels. Adult malarial mosquitoes, sitting on objects, are located at an angle to their surface with their heads down. The mandibular palps located on both sides of the proboscis are equal in length or slightly shorter.

The non-malarial mosquitoes pp.Culex and Aedes lay eggs that stick together in groups in small steel-gray rafts. The larvae are located under the water surface at an angle to it and have a long respiratory siphon on the penultimate segment. The respiratory horns of pupae are in the form of thin cylindrical tubes, and the mandibular palps of adult mosquitoes are short and reach no more than a third of the length of the proboscis. The body of non-malarial mosquitoes is held parallel to the surface on which they sit.

Mosquito control is most effective in relation to the aquatic stages of the life cycle - larvae and pupae. Land reclamation methods are used - backfilling ditches and quarries with stagnant water. It is possible to treat individual reservoirs with a high concentration of larvae and pupae with pesticides, as well as places of mass accumulations of sexually mature stages of mosquitoes in the daytime, sheds, cattle yards. The most effective are biological control measures in combination with hydro-reclamation measures carried out in accordance with state antimalarial programs. Thus, in Western Transcaucasia, it was possible to quickly reduce the number of mosquitoes and the incidence of malaria among the population due to land reclamation and breeding of fish - mosquitoes, which feed mainly on Diptera larvae. For personal protection, repellents and mechanical means are used: gauze curtains, nets, etc.

Vector-borne diseases are infectious diseases transmitted by blood-sucking insects and representatives of the arthropod type. Infection occurs when a person or animal is bitten by an infected insect or tick.

There are about two hundred official diseases that have a transmissible transmission route. They can be caused by various infectious agents: bacteria and viruses, protozoa and rickettsia, and even helminths. Some of them are transmitted through the bite of blood-sucking arthropods (malaria, typhus, yellow fever), some of them indirectly, when cutting the carcass of an infected animal, in turn, bitten by a vector insect (plague, tularemia, anthrax).

carriers

The pathogen passes through a mechanical carrier in transit (without development and reproduction). It can persist for some time on the proboscis, the surface of the body, or in the digestive tract of an arthropod. If at this time a bite occurs or contact with the wound surface occurs, then human infection will occur. A typical representative of a mechanical carrier is a fly of the fam. Muscidae. This insect carries a variety of pathogens: bacteria, viruses, protozoa.

As already mentioned, according to the method of transmission of the pathogen by an arthropod vector from an infected vertebrate donor to a vertebrate recipient, natural focal diseases are divided into 2 types:

obligate-transmissible, in which the transmission of the pathogen from the vertebrate donor to the recipient vertebrate is carried out only through a blood-sucking arthropod during blood-sucking;

facultative-transmissible natural focal diseases in which the participation of a blood-sucking arthropod (carrier) in the transmission of the pathogen is possible, but not necessary. In other words, along with the transmissible (through a bloodsucker), there are other ways of transmitting the pathogen from a vertebrate donor to a recipient vertebrate and a person (for example, oral, alimentary, contact, etc.).

According to E. N. Pavlovsky (Fig. 1.1), the phenomenon natural foci vector-borne diseases is that, regardless of the person in the territory of certain geographical landscapes, there may be foci diseases to which a person is susceptible.

Such foci were formed in the course of a long evolution of biocenoses with the inclusion of three main links in their composition:

Populations pathogens illness;

Populations of wild animals - natural reservoir hosts(donors and recipients);

Populations of blood-sucking arthropods - carriers of pathogens illness.

It should be borne in mind that each population of both natural reservoirs (wild animals) and vectors (arthropods) occupies a certain territory with a specific geographical landscape, which is why each focus of infection (invasion) occupies a certain territory.

In this regard, for the existence of a natural focus of the disease, along with the three links mentioned above (pathogen, natural reservoir and carrier) essential has a fourth link:

natural landscape(taiga, mixed forests, steppes, semi-deserts, deserts, various water bodies, etc.).

Within the same geographical landscape, there may be natural foci of several diseases, which are called conjugated. This is important to know when vaccinating.

Under favorable environmental conditions, the circulation of pathogens between carriers and animals - natural reservoirs can occur indefinitely. In some cases, infection of animals leads to their disease, in others, asymptomatic carriage is noted.

By origin natural focal diseases are typical zoonoses, i.e., the circulation of the pathogen occurs only between wild vertebrates, but the existence of foci is also possible for anthropozoonotic infections.

According to E. N. Pavlovsky, natural foci of vector-borne diseases are monovector, if in

the transmission of the pathogen involves one type of carrier (lice relapsing and typhus), and polyvector, if the transmission of the same type of pathogen occurs through carriers of two, three or more species of arthropods. The foci of such diseases are the majority (encephalitis - taiga, or early spring, and Japanese, or summer-autumn; spirochetosis - tick-borne relapsing fever; rickettsiosis - tick-borne typhus North Asian, etc.).

The doctrine of natural foci indicates the unequal epidemiological significance of the entire territory of the natural focus of the disease due to the concentration of infected vectors only in certain microstations. Such a focus becomes diffuse.

In connection with general economic or purposeful human activity and the expansion of urbanized territories, mankind has created conditions for the mass distribution of so-called synanthropic animals (cockroaches, bedbugs, rats, house mice, some ticks and other arthropods). As a result, humanity is faced with an unprecedented phenomenon of the formation anthropogenic foci of disease, which can sometimes become even more dangerous than natural foci.

Due to human economic activity, irradiation (spread) of the old focus of the disease to new places is possible if they have favorable conditions for the habitat of carriers and animals - donors of the pathogen (construction of reservoirs, rice fields, etc.).

Meanwhile, it is not excluded destruction(destruction) of natural foci during the loss of its members from the composition of the biocenosis, which take part in the circulation of the pathogen (during the drainage of swamps and lakes, deforestation).

In some natural foci, ecological succession(replacement of some biocenoses by others) when new components of the biocenosis appear in them, capable of being included in the circulation chain of the pathogen. For example, the acclimatization of the muskrat in natural foci of tularemia led to the inclusion of this animal in the circulation chain of the causative agent of the disease.

E. N. Pavlovsky (1946) identifies a special group of foci - anthropourgical foci, the emergence and existence of which is associated with any type of human activity and also with the ability of many species of arthropods - inoculators (bloodsucking mosquitoes, ticks, mosquitoes that carry viruses, rickettsia, spirochetes and other pathogens) to move to synanthropic lifestyle. Such arthropod vectors live and breed in settlements both rural and urban types. Anthropourgical foci arose secondarily; In addition to wild animals, domestic animals, including birds, and humans are included in the circulation of the pathogen, so such foci often become very tense. Thus, large outbreaks of Japanese encephalitis have been noted in Tokyo, Seoul, Singapore and other large settlements in Southeast Asia.

Anthropourgical character can also acquire foci of tick-borne relapsing fever, cutaneous leishmaniasis, trypanosomiasis, etc.

The stability of natural foci of some diseases is primarily due to the continuous exchange of pathogens between carriers and animals - natural reservoirs (donors and recipients), but the circulation of pathogens (viruses, rickettsia, spirochetes, protozoa) in the peripheral blood of warm-blooded animals - natural reservoirs is most often limited in time and lasts for several days.

Meanwhile, the causative agents of such diseases as tick-borne encephalitis, tick-borne relapsing fever, etc., multiply intensively in the intestines of tick-carriers, perform transcoelomic migration and are introduced with hemolymph into various organs, including the ovaries and salivary glands. As a result, an infected female lays infected eggs, i.e., transovarial transmission pathogen to the offspring of the carrier, while the pathogens in the course of further metamorphosis of the tick from the larva to the nymph and further to the adult are not lost, i.e. transphase transmission pathogen.

In addition, ticks retain pathogens in their body for a long time. EN Pavlovsky (1951) traced the duration of spirochaetonity in ornithodorin ticks to 14 years or more.

Thus, in natural foci, ticks serve as the main link in the epidemic chain, being not only carriers, but also persistent natural keepers (reservoirs) of pathogens.

The doctrine of natural foci considers in detail the methods of transmission of pathogens by carriers, which is important for understanding the possible ways of infecting a person with a particular disease and for its prevention.

Immunoprophylactic methods include immunization of the population. These methods are widely used for the prevention of infectious diseases. The development of immunoprophylaxis of invasions has a number of significant difficulties and is currently at the development stage. Measures for the prevention of natural focal diseases include measures to control the number of disease carriers (reservoir hosts) and arthropod vectors by influencing their habitat conditions and their reproduction rates in order to interrupt the circulation of the pathogen within the natural focus.

62. general characteristics protozoa (Protozoa) Overview of the structure of protozoa

This type is represented by unicellular organisms, the body of which consists of the cytoplasm and one or more nuclei. The cell of the simplest is an independent individual, showing all the basic properties of living matter. It performs the functions of the whole organism, while the cells of multicellular organisms are only part of the organism, each cell depends on many others.

It is generally accepted that unicellular beings are more primitive than multicellular ones. However, since the entire body of unicellular organisms, by definition, consists of one cell, this cell must be able to do everything: eat, and move, and attack, and escape from enemies, and survive unfavourable conditions environment, and multiply, and get rid of metabolic products, and protect themselves from drying out and from excessive penetration of water into the cell.

A multicellular organism can also do all this, but each of its cells, taken separately, is good at doing only one thing. In this sense, a cell of the simplest is by no means more primitive than a cell of a multicellular organism. Most representatives of the class have microscopic dimensions - 3-150 microns. Only the most major representatives species (shell rhizomes) reach 2-3 cm in diameter.

Digestive organelles - digestive vacuoles with digestive enzymes (similar in origin to lysosomes). Nutrition occurs by pino- or phagocytosis. Undigested residues are thrown out. Some protozoa have chloroplasts and feed on photosynthesis.

Freshwater protozoa have osmoregulatory organs - contractile vacuoles, which are periodically secreted into external environment excess fluid and dissimilation products.

Most protozoa have one nucleus, but there are representatives with several nuclei. The nuclei of some protozoa are characterized by polyploidy.

The cytoplasm is heterogeneous. It is subdivided into a lighter and more homogeneous outer layer, or ectoplasm, and a granular inner layer, or endoplasm. The outer integument is represented by either a cytoplasmic membrane (in amoeba) or a pellicle (in euglena). Foraminifera and sunflowers, inhabitants of the sea, have a mineral, or organic, shell.

Irritability is represented by taxis (motor reactions). There are phototaxis, chemotaxis, etc.

Reproduction of protozoa Asexual - by mitosis of the nucleus and cell division in two (in amoeba, euglena, ciliates), as well as by schizogony - multiple division (in sporozoans).

Sexual - copulation. The cell of the protozoan becomes a functional gamete; As a result of the fusion of gametes, a zygote is formed.

Ciliates are characterized by a sexual process - conjugation. It lies in the fact that cells exchange genetic information, but there is no increase in the number of individuals. Many protozoa are able to exist in two forms - a trophozoite (a vegetative form capable of active nutrition and movement) and a cyst, which is formed under adverse conditions. The cell is immobilized, dehydrated, covered with a dense membrane, the metabolism slows down sharply. In this form, the protozoa are easily carried over long distances by animals, by the wind, and are dispersed. When exposed to favorable living conditions, excystation occurs, the cell begins to function in a trophozoite state. Thus, encystation is not a method of reproduction, but helps the cell to survive adverse environmental conditions.

Many representatives of the Protozoa type are characterized by the presence of a life cycle consisting in a regular alternation life forms. As a rule, there is a change of generations with asexual and sexual reproduction. Cyst formation is not part of a regular life cycle.

The generation time for protozoa is 6-24 hours. This means that, once in the host organism, the cells begin to multiply exponentially and theoretically can lead to its death. However, this does not happen, since the protective mechanisms of the host organism come into force.

Of medical importance are representatives of the protozoa, belonging to the classes of sarcodes, flagellates, ciliates and sporozoans.