Classification of natural foci. vector-borne diseases

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Introduction

Characteristics of carriers

Bibliography

Introduction

Over the past decade, there has been an increase in human and animal diseases of an infectious and invasive nature, which is associated with a high prevalence of pathogens of the infectious process in nature. The spread of infection is facilitated by carriers that live everywhere, including those adjacent to humans.

The spread of a number of infections, which are carried by insects and ticks, makes it necessary to draw the attention of a wide range of medical and veterinary workers, as well as the public, to these issues.

In their diversity, the number of species, arthropods surpass all other groups of animals.

Arthropods have the greatest epidemiological significance as specific carriers of pathogens of human infectious diseases. In the body of a specific carrier, the pathogen goes through a certain cycle of development (malaria plasmodium in the body of a mosquito, leishmania in mosquitoes) or only multiplies (the causative agent of plague in fleas, the encephalitis virus in ticks). In mechanical carriers, pathogens are located on the surface of the body, in the proboscis, intestines (flies, horseflies, cockroaches). The transfer of the pathogen in such cases, as a rule, is possible for a short period of time, while it retains its viability. In some cases, the same species of arthropods can be a specific and mechanical carrier of some pathogens.

Ways of spreading infections

infectious invasive disease pathogen

Infectious disease vectors can be divided into three groups:

Carriers of pathogens of anthroponoses (malaria, typhus, etc.)

Carriers of pathogens of zooanthroponoses (plague, tularemia, boreliosis, etc.)

Carriers that circulate a human pathogen among animals.

The mechanism of transmission of pathogens by carriers includes three phases: obtaining the pathogen; transfer of a pathogen by a carrier from an infected person or animal to a healthy one; the introduction of a pathogen by a carrier into the human (animal) body.

The transfer of infectious agents can be mechanical and specific. During mechanical transfer, pathogens received by the carrier

Only for a while remain viable and virulent on the surface of his body or in the digestive tract.

Sometimes the same vector can be mechanical for one infection and specific for another. For example, mosquitoes of the genus Anopheles, being specific carriers of malaria pathogens, can be mechanical carriers of tularemia and anthrax pathogens.

The introduction of pathogens into the body of a healthy person (animal) occurs either at the time of bloodsucking, when they are introduced using the mouth apparatus of the carrier, or injected with its saliva.

This method of introduction is called inoculation. In another case, the carrier, upon contact with a person (animal), contaminates its skin, mucous membranes, wounds with its excrement or tissue fluid (for example, when crushing the carrier), which contain pathogens, or transfers them from the surface of the body, paws, proboscis, contaminated with substrates containing pathogens, food products and household items (for example, when transmitting pathogens of intestinal infections). This method of transfer is called contamination.

Inoculation and contamination can be mechanical or specific. Mechanical contamination is most common during the transmission of most intestinal infections and infestations by flies and cockroaches.

Mechanical inoculation is observed during the transmission of tularemia pathogens by mosquitoes, biting midges, midges, anthrax - mosquitoes, flies, stingers, horseflies. An example of specific inoculation is the transmission of plague by fleas, encephalomyelitis, yellow fever, malaria by mosquitoes, leishmaniasis and phlebotomy fever by mosquitoes. Specific contamination is somewhat less common. In this way, trypanosomes (causative agents of Chagas disease) are transmitted by the kissing bug, spirochetes and rickettsiae (causative agents of lice relapsing and typhus) by lice, as well as spirochetes of endemic relapsing typhoid by argas ticks.

A number of carriers are involved in the preservation of pathogens as a species by passing them on to their offspring (transovarial and transphase transmission). Transovarial transmission - the ability of female carriers to transmit the resulting pathogens to their offspring: they lay infected eggs, from which the subsequent phases develop (larvae, pupae or nymphs and adults) that retain pathogens.

Transphase transmission - the ability of the carrier to keep the pathogen during molting during the transformation of one phase into the next.

For example, an infected tick larva develops into an infected nymph, and the latter into an infected adult.

In the transmission of pathogens of a contagious disease, carriers of several species can sometimes be involved, some of them are main, others are secondary.

The first are characterized by: large numbers populations, high activity of individuals, in particular regarding attacks on people, increased infectivity with pathogens in relation to them.

The most important in the transmission of infectious agents to humans are the so-called synanthropic types of vectors, i.e. species whose life is associated with humans. Synanthropic carriers are usually divided into endophilic (endophiles), who spend most of their lives in human buildings, and exophilic (exophiles) inhabitants of open space.

Depending on the climate, landscape, economic and living conditions, the same type of carrier can be the main one in one epidemic focus and a secondary one in another.

Characteristics of carriers

Argas mites are found mainly in the southern regions of the country. Their infection with pathogens of viral, rickettsial, bacterial etiology was revealed. Argas ticks are of the utmost importance as specific carriers of Borrelia. Due to the long life cycle (according to some sources - up to 25 years), foci of tick-borne spirochetosis are firmly rooted in nature. In the last 10 - 15 years, argas mites are increasingly found in urban-type buildings.

Diptera (mosquitoes, midges, midges, horseflies) are carriers of pathogens of many infectious diseases of humans and animals (tularemia, anthrax, etc.). Their role in the transmission of viruses is great. Mosquitoes have the greatest epidemiological significance in this group of insects. They carry malaria, West Nile, yellow fever, dengue, Sindbis, Japanese encephalitis and many others.

Wild, domestic and ornamental birds are the source of the causative agent of ornithosis. It should be noted a high degree of infection of pigeons, crows (up to 50%). The most important is the air-dust route of transmission of infection, the smaller one is airborne and food.

Wild mammals (fox, wolf, jackal, raccoon, raccoon dog, bats) in whose population the rabies virus circulates are dangerous to humans. In addition to natural foci, secondary anthropurgic foci are formed, in which the virus circulates between dogs, cats, and farm animals.

Goats, sheep, cows, pigs, deer are the main sources of brucellosis pathogen.

Thus, it is necessary to prevent the occurrence of infectious processes not only by active and passive immunization, but also to prevent the collision of infectious animals with humans.

Based on many years of scientific and experimental research, a system of protection against blood-sucking and non-blood-sucking arthropods has been developed, taking into account the climatic, geographical, ecological and epidemiological characteristics of geographical regions.

Currently, preventive and therapeutic vaccines have been developed against many infectious diseases with which it is necessary to vaccinate the population in endemic areas. And also observe the sanitary and epidemiological regime at agricultural and food enterprises and places of food storage.

Bibliography

1. http://www.gkb2.grodno.by/health/gkb2/ing8/

2. http://46cge.rospotrebnadzor.ru/info/105628/

3. http://nd-ek.ru/nas

4. http://dic.academic.ru/dic.nsf/enc_medicine/22944/%D0%9F%D0%B5%D1%80%D0%B5%D0%BD%D0%BE%D1%81%D1 %87%D0%B8%D0%BA%D0%B8

5. Infectious diseases, ed. N.D.Yuschuk, Yu.Ya.Vengerova

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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 carriers only in certain microstation. 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 of 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 under development. Measures for the prevention of natural focal diseases include measures to control the number of carriers of the disease (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 adverse environmental conditions, and multiply, and get rid of metabolic products, and to be protected 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 largest representatives of the 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 periodically release excess fluid and dissimilation products into the external environment.

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 phylum are characterized by the presence of a life cycle consisting in a regular alternation of 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's body, the cells begin to multiply exponentially and theoretically can lead to its death. However, this does not happen, since the defense mechanisms host organism.

medical significance have representatives of protozoa belonging to the classes sarcode, flagella, ciliates and sporozoa.

Vectors are invertebrates such as arthropods that spread vector-borne diseases among humans and animals. Carriers include blood-sucking insects - fleas (see), mosquitoes (see), midges (see Gnus), mosquitoes (see), midges (see), etc., as well as ticks (see) - ixodid, argas, gamas, krasnotelkovyh, etc. The objects of transfer can be bacteria, viruses, and helminths. The transfer of the pathogen is mechanical and specific. In the first case, there is no biological connection between the carrier and the causative agent of the disease. With a specific transfer, there is such a connection and the pathogen goes through a certain development cycle in the body of the carrier (for example, with malaria), until the end of which the carrier is not dangerous for a healthy organism. Infection occurs either during bloodsucking or by contamination of the skin with feces that contain pathogens.

Vector control - important element prevention of the diseases they spread and should be carried out taking into account the biological and ecological characteristics of the carrier species.

Carriers are invertebrate animals such as arthropods (Arthropoda) that spread pathogens of human and animal diseases. Carriers include blood-sucking insects (fleas, lice, mosquitoes, midges, mosquitoes, midges) and ticks - ixodid, argas, gamas, red-haired, transmitting pathogens of infections or invasions to animals or humans at the time of blood-sucking or when they are crushed on damaged skin (lice) . Non-blood-sucking insects (ants, flies, cockroaches) that can carry pathogens on their paws and body hairs can also infect.

The ways and mechanisms of infection of humans and animals through vectors are varied. They depend on the biological relationship between the carrier and the pathogen. In one case, the pathogen, getting to the insect from the donor, remains, without multiplying, on its mouthparts, integuments of the body or in the digestive tract. The carrier transmits the pathogen to healthy animals or humans through repeated bloodsucking or contact with them. This method of transmission is called mechanical. So, mosquitoes and horseflies transmit tularemia and anthrax bacteria to humans, flies and cockroaches - pathogens of intestinal infections, etc.

More often, the pathogen multiplies in the body of the carrier and passes part of its life cycle in it. In such cases, transmission may not occur before the time when the pathogen reaches a certain infecting stage during its development in the carrier. For transmission to occur, it is often necessary for the pathogen to move to certain tissues and organs of the carrier, from where it will be possible to exit (salivary glands, intestines). Such a transfer is called specific. Some pathogens not only multiply in the body of the carrier, remain in it at all phases of metamorphosis (see), but can be transmitted to the offspring of the carrier transovarially, that is, through the egg (see. Transovarial transmission of infection). With such a relationship with the pathogen, the arthropod is no longer only a carrier, but also the host of the pathogen (Dermacentor ticks and tick-borne typhus rickettsia; Ornithodorus ticks and relapsing fever spirochetes; ixodid ticks and piroplasms, etc.).

E. N. Pavlovsky called the diseases that insects and ticks infect a person with transmissible. These are malaria and Japanese encephalitis transmitted by mosquitoes; leishmaniasis and mosquito fever, which are transmitted by mosquitoes; typhus and relapsing fever transmitted by lice; tick-borne encephalitis, tick-borne relapsing fever and endemic rickettsiosis, the pathogens of which are transmitted by ticks, etc. These diseases are characterized by natural foci (see), due, in particular, to the long-term persistence of pathogens in the body of arthropods. The period of carrier activity determines the seasonality of human diseases.

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. Transfer of a pathogen by a specific vector healthy body is possible not 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 dated July 2, 1999 contains a list of diseases that require measures to sanitary protection territories, which mentions such infections as plague, malaria and yellow fever, the causative agents of which are carried by insect-specific vectors. Decree of the Government of Russia No. 715 dated 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, acariasis, 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

Disease	2007	2008	2009	2010	2011	2012	2013	2014*
Tularemia	831	96	57	115	54	115	1063	72
Tick-borne borreliosis	7247	7251	9688	7063	9957	8286	5715	5355
Tick-borne viral encephalitis	3138	2817	3721	3108	3544	2732	2255	1858
Q fever	84	17	124	190	190	190	171	31
West Nile fever	-	-	-	-	166	454	209	27
kgl	-	-	116	69	99	74	80	90
Leptospirosis	710	619	495	369	-	251	255	202
Pediculosis	268602	288333	272688	266694	218861	265579	257707	193761
Brill disease	0	0	2	2	2	1	2	2
Typhus	0	0	0	0	0	0	0	0
Malaria first identified	128	84	108	106	86	87	95	65
Hepatitis B acute	7523	5750	3844	3179	2449	2022	1904	1326

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 vector 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 the 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:

• 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 of arthropods

1. Carriers of pathogens (mechanical and specific).
2. Causative agents of diseases (scabies mite, lice)
3. Intermediate hosts of helminths ( Diptera- 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 size of the body of ixodid ticks is from 5 to 25 mm. They live in open spaces (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 (stigmata, 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 intense 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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