In nature, there are several types of relationships between organisms that have varied effects on each other.

The impact of one species on another can be either neutral or positive, or negative. In addition, there are different combinations of such relationships. There are:

• symbiosis;
• neutralism;
• antibiosis.

Symbiosis- a form of relationship between two organisms from which both benefit.

Neutralism- a type of biological connection that consists of two organisms living in the same territory, but they are not connected to each other and do not directly influence each other.

Host organisms can be:

• bacteria;
• protozoa;
• plants;
• animals;
• Human.

• ubiquitous, found everywhere;
• tropical, which are found only in hot, tropical climates.

• dirty hands;
• animal hair;
• poorly prepared foods (nutritional factor);
• contact and household factor;
• transmissible;
• percutaneous.

Animals and their fur– are a source of infection with roundworms and lamblia. For example, pinworm eggs that have fallen from an animal's fur remain viable for a long time (up to about 6 months) and, once on carpets, clothes, bedding, children's toys and hands, penetrate the food tract.

• through poorly washed vegetables and fruits;
• poorly prepared food (most often meat);
• contaminated water.

For example, improperly prepared shish kebab, dried meat or homemade lard can infect a person with trichinosis and echinococcus, and poorly prepared dry fish or caviar can cause infection with opisthorchiasis and tapeworm.

Transmission method infection occurs with the help of blood-sucking insects, for example: ticks, mosquitoes, lice, fleas, bedbugs.

Contact - household way infection occurs through an infected person or animal, through contact or through the use of common household items.

Percutaneous method infection occurs during swimming in bodies of water or through contact with contaminated soil. The larvae enter the body through human mucous membranes or skin during contact with water or contaminated soil.

As a rule, a person asks such a question when his health is seriously undermined. It is common for a person to brush off a problem at its initial stage until it develops into a serious form and affects his well-being.

• visual identification (if penetration has occurred from the outside through the skin);
• microscopic examination.

External and internal manifestations of infection

• skin rash;
• burning;
• hyperemia;
• feverish condition;
• Quincke's edema.

It is important to know that the degree of development of allergies depends on many factors:

Disturbances in the functioning of the body during internal invasion include the following symptoms:

Disturbances in the gastrointestinal tract, which are manifested by the following symptoms:

• intestinal spasms;
• irritable bowel syndrome;
• flatulence;
• constipation or diarrhea;
• change in color of feces;
• itching in the anus;
• visual detection of helminths;
• the presence of worms in the vomit.

Since worms can reach significant sizes in the body, they can physically impede the passage of feces and disrupt the functioning of other organs, such as the bile ducts.

There are other methods for identifying “dependents”, the so-called string test. A string with a capsule is inserted into the patient's intestines through the nose and removed four hours later along with the samples obtained.

Another method is colonoscopy, during which a specialist examines the condition of the inner surface of the colon using a special probe.

Modern preparations based on herbal ingredients will help satisfy all three of the above points:

• "Methosept+";
• "Regesol";
• "Imcap";
• "Fomidan";
• "Vitanorm+";
• "Maxifam+";
• "Neuronorm";
• "Bactrum".

All these drugs are modern drugs of the latest generation and have a certain therapeutic effect. The use of these drugs in combination allows you to combine their therapeutic effect and obtain remarkable results.

The priority of anthelmintic drugs is based on:

• efficiency;
• security;
• the possibility of combining several drugs for a better therapeutic effect.

Prepare tea as follows: take one tablespoon of the following plants: oak bark, buckthorn, wormwood, tansy. Then one tablespoon of the plant mixture is poured into 500 ml of boiling water and left in a sealed container overnight. In the morning on an empty stomach, drink 100g of the resulting tincture. Treatment continues for two to three weeks.

given by lice, were not released into the external environment, but were deposited and developed here, on the host.

. inoculation, when the pathogen enters the host’s blood through the arthropod’s mouthparts directly through blood sucking;

. contamination, when the pathogen is released by arthropods in feces or otherwise onto the host’s body, and then enters the bloodstream through damage to the skin (wounds, scratches, etc.).

The causative agents of a number of diseases can be transmitted “vertically” from mother to fetus, sometimes repeatedly (for example, with toxoplasmosis in rodents). In this case, transmission of the pathogen will be transplacental.

Even more rare cases transfusion infection during the provision of obstetric surgical care, blood transfusion (blood transfusion) or organ transplantation.

Multicellular organisms are characterized by a high degree of development of the reproductive system and the formation of a huge number of reproductive products. This is facilitated by the primary hermaphroditism of flatworms, the initially high fertility of roundworms and the bulk of arthropods. Often the high intensity of sexual reproduction is complemented by reproduction of larval stages life cycle. This is especially true for flukes, whose larvae reproduce parthenogenetically, and in some tapeworms, by internal or external budding.

oilers, annelids and arthropods) and have preservative properties of enzymes of the digestive system (in annelids and arthropods).

A person becomes infected diphyllobothriasis And opisthorchiasis, eating fish that has undergone insufficient heat treatment. This route of infection is unlikely for a child. East African trypanosomiasis more common among middle-aged people - hunters, travelers, members of geological exploration parties in the uninhabited savannahs of Africa. This pattern often manifests itself in intermediate hosts: large adult fish have more opportunities to become carriers of metacercariae of flukes or plerocercoids of tapeworms than small juveniles.

The likelihood of infection also often depends on the profession. So, balantidiasis workers on pig farms are more likely to become infected, taeniasis And teniarincho-

zom- meat processing plant workers, hookworm infections in temperate latitudes - miners, and in the tropics - agricultural workers. Diphyllobothriasis fishermen are more often infected, and alveococcosis- hunters and persons involved in the processing of fur raw materials.

Persons with severe forms of malignant tumors, as a rule, do not become infected with visceral leishmaniasis. Iron deficiency anemia practically protects a person from malaria, while treatment with iron supplements aggravates the severe course of this disease.

Malignant tumors of the colon and female reproductive system aggravate the course of amebiasis and trichomoniasis.

Damage to the peripheral nervous system aggravates the course of scabies. All immunodeficiency conditions (AIDS, treatment with corticosteroid hormones and immunosuppressants) lead to aggravation of the course of most invasive diseases. For example, cryptosporidiosis is an acute, short-lived disease that ends in spontaneous recovery, but in HIV-infected people it is severe and, in the absence of adequate therapy, ends in death. In immunocompetent individuals, latent toxoplasmosis often reactivates against the background of HIV infection and affects the lungs, central nervous system, lymph nodes, and myocardium. Unlike classic Mediterranean visceral leishmaniasis, which is also called childhood leishmaniasis, since it is recorded mainly in children, visceral leishmaniasis in adults with HIV becomes malignant and is accompanied by resistance to specific drugs, as a result of which the patient’s life expectancy is reduced.

In non-immune persons traveling to countries in the tropical zone, many tropical diseases are more severe than in native residents.

The role of genetics was first assessed in experimental models in which environmental changes can be controlled and measured. Animal research has led to the discovery of the most interesting gene NRAMP1 which appears to play an important role in the formation of innate immunity against intracellular pathogens.

Recent studies in schistosome-infected populations have taken advantage of new epidemiological and genetic techniques that allow integrated and simultaneous assessment of the role of environmental and host-specific factors in the control of infection and disease. This work allowed the discovery of two main loci, one of which controlled the level of infection, and the other controlled the development of the disease.

In the case of filariae or schistosomes, individuals from endemic areas will become infected throughout life as a result of prolonged exposure and failure to acquire protective immunity. Host immunity usually develops slowly and is almost never complete.

Convergent evolution of tropomyosins 1 and 2 S. mansoni and their intermediate host Biomphalaria glabrata, which share ~63% homology is believed to be a form of molecular mimicry. Tropomyosin belongs to a family of proteins associated with the contractile activity of actin and myosin. It is ubiquitously expressed in invertebrates and vertebrates, but there are many isoforms that differ structurally and functionally. A relatively high degree of homology and functional similarity has been shown between tropomyosin of phylogenetically distant species, including helminths (S. mansoni, O. volvulus, Brugia pahangi).

In clinical immunology, the highly conserved muscle protein tropomyosin is of interest as a cross-reactive protein between many common allergens, including mites, shrimp and insects. It has been suggested that a "general allergy" to insects may develop in people who have previously been sensitized to one or more insects, and that the allergenic similarity may possibly extend to other non-insect arthropods.

Particular attention was paid to homologous antigens in domestic cockroaches (Blatta germanica And Periplaneta americana) and house dust mites (Dermatophagoides pteronyssinus And D. farinae), because they play a very important role in allergy diseases.

Interesting homologies in the schistosome genome include complement protein Clg, insulin-like receptor, insulin-like growth factor binding protein, and the tumor necrosis factor family, as well as homologies of genes associated with B and T lymphocytes, such as pre-B-enhancing factor cells (PBEF).

A high degree of sequence homology and structural similarities have been shown for human and helminth C-type lectins (C-TLs). One explanation for this is that host hormones are a key mechanism in maintaining helminth development and maturation, including sexual development.

Protozoa that live outside cells are covered with antibodies and, in this form, lose their mobility, making it easier for them to be captured by macrophages.

Antibodies do not attach to intact helminth integuments, so immunity in case of helminthic diseases, partial (and as a consequence unstable) and acts mainly against larvae: the development of migrating worm larvae in the presence of antibodies slows down or stops. Some types of leukocytes, in particular eosinophils, are able to attach to migrating larvae. The body surface of the larvae is damaged by lysosomal enzymes, which facilitates tissue contact with antibodies and often leads to the death of the larvae. Helminths attached to the intestinal wall can be exposed to the mechanisms of cellular immunity in the mucous membrane, and due to intestinal peristalsis, helminths are released into the external environment.

The main role in the development of cellular immunity belongs to T-lymphocytes. Upon antigen recognition, T cells differentiate into memory T cells and effector T cells. These specialized T cells function in several ways. For example, memory T cells return to a “resting” state and serve as a source of new antigen-specific T cells whenever the same antigen may re-enter the body. Effector T cells can be functionally divided into two groups: T helper cells (Th) and cytotoxic T cells (Tc). The original type of Th cell can be differentiated into subgroups of cells that differ in the secreted cytokines: Th-1 and Th-2 cells. Most T cell activity involves the synthesis and release of various chemical mediators called cytokines. Cytokines interact with a variety of cells required for a range of immunological processes. Th-1 cells typically secrete interleukin-2 (IL-2), interferon-γ (IFN-γ) and tumor necrosis factor (TNF). These cytokines support the inflammatory process, activate macrophages and induce the proliferation of natural killer (NK) cells. Th-2 cells typically secrete several cytokines, including IL-4, IL-5, and IL-10. They activate B cells and immune responses that depend on humoral antibodies. As a rule, the predominance of Th-1 is associated with the acute course of infection and subsequent recovery, Th-2 - with the chronic course of the disease and allergic manifestations. Th-1 cells provide protection against intracellular protozoa, Th-2 cells are necessary for the expulsion of intestinal helminths.

. deterioration of health of varying degrees, up to the death of the owner;

Inhibition of the reproductive (reproductive) function of the host until his death;

Changes in the host's normal behavioral reactions;

Intestinal epithelial cells infected with cryptosporidium undergo a number of pathological changes, which leads to a reduction in the absorptive surface of the intestine and, as a result, impaired absorption of nutrients, especially sugars.

Intestinal helminths damage the intestinal mucosa with their hooks and suckers. The mechanical effect of opisthorchis is to damage the walls of the bile and pancreatic ducts and the bile duct.

zyra suckers, as well as spines covering the surface of the body of young helminths. With echinococcosis, there is pressure from the growing bladder on the surrounding tissues, resulting in their atrophy. Schistosome eggs cause inflammatory changes in the bladder and intestinal walls and may be associated with carcinogenesis.

The mechanical effect of helminths, sometimes very significant, may be associated with the characteristics of the biology and development of helminths in the host body. For example, the death of a huge number of villi occurs with the massive development of dwarf tapeworm cysticercoids in them, and the deeper tissues of the intestinal wall are often damaged. When roundworms are localized in the intestinal lumen, they rest their sharp ends against its walls, damaging the mucous membrane, causing a local inflammatory reaction and hemorrhage. Violation of the integrity of the tissues of the liver, lungs and other structures of the host can be very serious as a result of the migration of the larvae of some nematodes (roundworm, hookworm, necator).

Changes in the host's normal behavioral reactions. Directed modulation of host behavior facilitating pathogen transmission has been noted in

Antigenic variability of surface proteins during the molting period is also known for roundworm larvae during migration in the body.

Protein disulfide isomerase produced by micro- and macrofilariae Onchocerca volvulus- the causative agent of onchocerciasis, leading to irreversible blindness, is identical to the protein that is part of the retina and cornea. Tapeworms have an antigen similar to the human blood group B antigen, and the bovine tapeworm has an antigen similar to the blood group A antigen.

Trypanosomes are also capable of synthesizing surface antigens that are so similar to host proteins that the body does not recognize them as foreign.

Immunosuppression. Suppressing the host's immune system allows pathogens to survive in the host's body. This applies to both humoral and cellular responses. Among the many physiological factors that cause insufficiency of the immune system, the dominant one should be recognized as the impact of pathogens, among which helminths play a leading role. Helminths can disrupt the physiology of the host's immune system by producing soluble chemical compounds that have a toxic effect on lymphocytes. Suppression of the immune response mainly occurs through inactivation of macrophages.

For example, in malaria, the pigment hemozoin accumulates in macrophages - a product of the breakdown of hemoglobin, which suppresses various functions of these cells. Trichinella larvae produce lymphocytotoxic factors, and schistosomes and the causative agent of American trypanosomiasis produce enzymes that destroy IgG antibodies. The causative agents of malaria and visceral leishmaniasis are capable of reducing the production of interleukins and, at the same time, the ability of T-helper cells to produce lymphokines necessary for the growth and differentiation of B-lymphocytes. This in turn disrupts the formation of specific antibodies. Entamoeba histolytica can produce special peptides that promote the survival of amoeba trophozoites in the human body by inhibiting the movement of monocytes and macrophages. Synthesis E. histolytica neutral cysteine ​​proteinase promotes the breakdown of human IgA and IgG, which ultimately ensures their effective protection against nonspecific and specific resistance factors of the macroorganism. Essential in the development of chronic forms of giardiasis is the ability of Giardia to produce IgA proteases, which destroy host IgA and other proteases.

oxygen produced in the cells of the immune system. Some nematodes and trematodes have developed a mechanism for damaging antibodies by secreting proteases that break down immunoglobulins.

helminths and bacteria from feces on food by flies, cockroaches and other arthropods.

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

Such foci were formed in the process of long-term evolution of biocenoses with the inclusion of three main links in their composition:

Populations pathogens illness;

Wildlife populations - natural reservoir hosts(donors and recipients);

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

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, due to which 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 vector), the fourth link is also of utmost importance:

. natural landscape(taiga, mixed forests, steppes, semi-deserts, deserts, various bodies of water, 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 vectors and animals - natural reservoirs - can occur indefinitely. In some cases, infection of animals leads to their illness, in others there is asymptomatic carriage.

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

Rice. 1.1. E. N. Pavlovsky is the founder of the doctrine of natural focality.

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

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

The doctrine of natural focality 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 center becomes diffuse.

In connection with general economic or purposeful human activity and the expansion of urban areas, humanity has created conditions for the mass spread 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 diseases, which can sometimes become even more dangerous than natural foci.

Due to human economic activity, it is possible for the old focus of the disease to irradiate (spread) to new places 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 when its members that take part in the circulation of the pathogen fall out of the biocenosis (during the drainage of swamps and lakes, deforestation).

In some natural foci there may be an ecological succession(replacement of one biocenosis by another) when new components of the biocenosis appear in them, capable of being included in the pathogen circulation chain. 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 disease pathogen.

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

Foci of tick-borne relapsing fever, cutaneous leishmaniasis, trypanosomiasis, etc. can also acquire an anthropourgic character.

The stability of natural foci of some diseases is explained primarily by 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 several days.

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

In addition, ticks retain pathogens in their bodies for a long time. E. N. Pavlovsky (1951) traced the duration of spirochete carriage in ornithodorine 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 guardians (reservoirs) of pathogens.

The doctrine of natural focality examines 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.

As already indicated, 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 pathogen is transmitted from a donor vertebrate to a recipient vertebrate only through a blood-sucking arthropod during blood sucking;

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

In the course of studying the natural focality of plague, tularemia, tick-borne encephalitis, cutaneous and visceral leishmaniasis and other infections and invasions, it turned out that each natural focus is an individual phenomenon, existing in nature in the singular, and the boundaries of the natural focus can, in principle, be established on the ground and shown on the map.

Currently, according to various sources, more than 40 human diseases are known on the territory of Russia, the foci of which can independently exist in nature, regardless of human economic activity. The carriers of their pathogens are about 600 species of vertebrates. Terrestrial vertebrates (mammals, birds, reptiles and in some cases amphibians) They are the feeders of many hundreds of species of blood-sucking arthropods, among which many dozens of species of guardians and carriers of pathogens have been identified.

Large epidemics of completely unknown previously severe febrile natural focal diseases have occurred in Africa and South America in recent decades (Argentine and Bolivian hemorrhagic fevers, Lassa fever, etc.). The existence of natural foci of diseases is confirmed, the causative agents of which have themselves been known for quite a long time.

Thus, the role of arthropods in the spread of pathogens can be represented in the form of a diagram (Scheme 1.1).

From diseases viral etiology, in addition to tick-borne and Japanese encephalitis, natural focality has been established for West Nile encephalitis (common in Equatorial and East Africa), Australian encephalitis (Murray Valley encephalitis), St. Louis encephalitis, equine encephalitis, yellow jungle fever, dengue fever, Kyasanur forest disease of India and etc. Some diseases of viral etiology are also found in our country: Omsk hemorrhagic fever, Japanese and taiga encephalitis, Crimean hemorrhagic fever, pappataci fever, rabies, etc.

Among rickettsial diseases natural focality is inherent in Tsutsugamushi and American Rocky Mountain fevers, tick-borne typhus in Asia and Africa, Q fever and other vector-borne rickettsial diseases.

Among spirochetosis Typical natural focal obligate-transmissible diseases are tick-borne relapsing fever (caused by

Scheme 1.1. Diseases transmitted by arthropods

tel - Obermeyer's spirochete), tick-borne borreliosis, of which the so-called village spirochetosis is of greatest epidemic importance.

In addition to tularemia and plague, bacterial Diseases such as pseudotuberculosis, brucellosis, yersiniosis, etc. have etiology in our country.

Protozoans vector-borne invasions, characterized by a pronounced natural focality, are found in tropical and subtropical countries. These include leishmaniasis, trypanosomiasis, etc.

Natural focality extends to some helminthiases: opisthorchiasis, paragonimiasis, dicroceliosis, alveococcosis, diphyllobothriasis, trichinosis, filariasis.

In recent years, certain areas have begun to be considered natural focal areas. mycoses- endemic diseases that occur due to a deficiency of microelements in soil and plants.

The doctrine of natural focality substantiates the connection between natural and anthropourgic foci of diseases, knowledge of which is important for epidemiological and epizootological assessment, especially in newly developed territories, and provision of possible preventive measures.

E. N. Pavlovsky pointed out that neutralization activities and subsequent elimination of a natural outbreak should be aimed at disrupting the continuous circulation of the pathogen by any means that influence its stages.

The system of these activities is as follows:

Decrease in the number and extermination of animals - donors of the pathogen;

Direct and indirect control of vectors based on knowledge of their biology and ecology;

Destruction of vectors in farm and domestic animals;

Rational economic measures that exclude an increase in the number of vectors;

Protective measures against attacks by vectors: use of repellents, special suits, etc.;

Specific prevention through vaccination with mono-vaccines, and in conjugate areas - with poly-vaccines.

The teachings of E. N. Pavlovsky provide the keys to preventive medicine and veterinary medicine not only to the study of natural focal infections and invasions, but also to the systematic, conscious elimination of natural factors that negatively affect the health of humans or farm animals. It has spread beyond the borders of our country and on its basis work is being fruitfully carried out in many foreign countries.

Food, in whatever form, is essential for the survival of living things. Millions of years have resulted in a variety of foraging strategies, and these different interactions are the glue that binds everything together.

Some feeding strategies are more familiar to us, such as carnivores (and plants), which eat other animals, and herbivores, which eat plants. However, there are different types of symbiotic relationships that involve closer and more complex interactions.

It is a partnership between organisms in which each of the life forms involved benefits the other.

This is when one organism uses another for its own purposes, but without causing obvious harm to it. An example is mosses growing on the bark of a tree.

Gaul

Some galls, such as inknuts on oak leaves (caused by wasps), support insect communities, which in turn can provide food for birds. Look at the crown of a birch tree and you will see dense branch structures that look a lot like birds' nests. This is the result of infection with fungi of the species - Taphrina betulina.

Different types of “freeloaders” have their own preferences, or preferred habitats. This happens:

• transmissibly, through blood-sucking insects;
• placentally, from mother to embryo, or into the fetus;
• contact-sexual method.

Optional forms

Important Features

The residence time of a facultative helminth in the host’s body may depend on its size, speed of spread and transmission to another individual, and nutritional efficiency. In the latter case, we are talking about the amount of nutrients that are available to the helminth at different stages of existence.

Many organisms have complex developmental cycles. They have to use two or three hosts, which belong to different species, only one of them will be a person.

How dangerous are flukes for humans?

Characteristic features of the structure

Flukes are classified as flatworms, of which there are over 7 thousand species in modern science. Flatworms, or Plathelminthes, include 3 classes:

• Eyelash worms;
• Tapeworms;
• Flukes.

Most eggs and larvae die due to the low probability of meeting a new intermediate host, however, the high fertility of each surviving individual perfectly covers the losses incurred. The type of flatworms of the class of flukes differs from tapeworms and ciliated worms in some structural features.

Sexual reproduction

All flatworms have organs located on both sides of the body (the so-called bilateral structure), the space between the internal organs is filled with parenchyma (loose connective tissue), and they already have organ systems (nervous, reproductive, muscular, excretory and digestive). Just like other flatworms, flukes are hermaphrodites that have male and female reproductive systems.

A sexually mature individual always settles in the body of the host - a mammal or vertebrate, where it reproduces eggs. In the sexually mature period, trematodes have a leaf-shaped body, which, due to the absence of internal cavities, is completely supplied with the resulting nutrients, and its existence and nutrition is ensured by a powerful sucker mouth, and, in some species, by spines with which they are attached in the right place. Marita (a sexually mature individual) is equipped with everything necessary to release eggs.

Fertilization in flukes occurs internally, in a cross way. The eggs are supplied with nutrients from the vitelline, receive a shell in the shell glands, mature in the uterus, after which the marita releases eggs, which must enter the external environment through the intestines of the intermediate host, and there they will certainly end up in the water. In the water, a miracidium (larva with eyes and cilia) emerges from the egg, which goes in search of a new intermediate host.

The next stage of fluke development is its new intermediate host, a gastropod, which is strictly unique and specific for each fluke. In the body of the mollusk, the miracidium turns into a sporocyst, which has only female genital organs. The sporocyst reproduces by parthenogenesis.

Parthenogenesis of the sporocyst, at a certain stage of its development, leads to the appearance of multicellular redia, which also reproduce by parthenogenesis and generate, in the last generation of their development, in cercariae. The cercariae leave the body of the mollusk, and must then either enter the body of a new intermediate host, or, if this does not happen, encyst on the grass.

Most of these forms enter the body of cattle, which eat grass along with cercariae, but the main part dies because it is incapable of searching on its own. Those of them who are lucky enough to get into the body of the final host make their way into the organ necessary for their habitat, and after reaching sexual maturity they live and release eggs again.

The general characteristics of the class of flukes may have some differences in each specific species, such as:

• in the form of a mollusk in which sporocysts live, followed by redia;
• in the structure of the testes, which in the liver fluke are branched, while in others they are compactly arranged.

But the common essence of the structure and sexual stages became the reason for their unification into a group of flukes, which differ from other types of flatworms.

Species and representatives of the class

The most common:

The primary routes of penetration of trematodes into the human body are orally, and usually through food. The causative agent of opisthorchiasis penetrates through river or lake fish that have not been subjected to heat treatment, or have not been sufficiently boiled or fried. From the intestines, the pathogen easily penetrates into the blood, after which it reaches the bile ducts, which constitute its natural habitat in the human body.

Schistosomes enter the body when a person swims in an infected river or lake. Schistosome eggs can be laid in the abdominal organs, where they enter through the intestines.

Pulmonary flukes, as their name suggests, live in the lungs and can enter the human body through infected pork, or through eaten crayfish and crabs. The symptoms of the disease are painful and, starting with cough and shortness of breath, can cause bradycardia, which can also be fatal.

Once in the intestine, the larva almost immediately sheds its shell and rushes through the bloodstream to the liver. The colonization of liver tissue by the liver fluke leads to the destruction of healthy cells, for which it needs spines and a sucker. An enlarged liver leads to bleeding and subsequent cirrhosis.

Another threat to human health is the fact that they do not show any special signs until they reach puberty, but by that time the internal organs of their carrier are already damaged and it is discovered that there are a huge number of them in the body.

The main trouble with such an infection is its second wave, when formed individuals begin to populate not only those organs where they usually exist. Penetration of flukes in a secondary lesion into the central nervous system and brain almost always leads to death.

Prevention of trematode infection

Prevention of the disease in different cases consists of various measures that a person should take in everyday life. In many cases, the cause of the disease is failure to comply with sanitation and hygiene rules, or eating unprocessed foods. In order to avoid infection with flatworms, including flukes, a person must take daily precautions.

Wash vegetables and fruits, especially greens thoroughly. Do not swim in random bodies of water or swallow water from them. Do not drink unboiled water, and do not eat undercooked meat or fish.

The division into types, as already indicated, is based on the degree of dependence on the host.

Thanks to this indicator, two main types can be distinguished:

The former, preferring a certain type of multicellular organism as a habitat, can, on occasion, live in another, completely different morphology. At the same time, they can also exist in the external environment for a fairly long period of time. A prominent representative is fungi. Once in the human body, they cause the development of subcutaneous diseases.

This determines the colossal fertility of most of these organisms - some of them can lay up to several million eggs per day.

The almost complete absence of the nervous system (it is present in its most primitive form - for example, in the peripharyngeal nodes) and sensory organs refers precisely to “cutting off the unnecessary.” This is due to constant presence in an environment with stable conditions: temperature, light level, acidity, etc.

Helminths

The most prominent representatives are the following:

Once in the human body, they cause many serious pathologies.

Bottom line

Considering that they most often cause the development of serious diseases, it is necessary to know and follow preventive measures against infection with them. And at the first sign of the opposite, contact a specialized specialist to undergo the necessary examination and prescribe adequate treatment.

Classification depending on the number of hosts.

Depending on the development cycle and characteristics of infection, there are the following groups of helminthiases:

Biohelminthiases are helminths whose life cycle occurs with a change of hosts, or the development of all stages occurs within one organism without exiting into the external environment (flukes, Trichinella).

Geohelminthiases are helminths, the eggs or larval stages of which develop in the external environment of the earth (ascaris, crooked head). Contact helminths are helminths, the invasive stage of which can enter the body of a healthy person through direct contact with patients (dwarf tapeworm, pinworm). Autoinvasion and superautoinvasion are characteristic.

Inspection of stool.

When examining feces (macroscopic method), helminths, their heads, strobila fragments, and segments released independently or after deworming can be found in them. This method is especially recommended for identifying pinworms and pork tapeworm segments.

Small portions of feces are mixed with water in a flat tray or Petri dish and, viewing in good light against a dark background, if necessary, using a magnifying glass, tweezers or pipette, all suspicious formations are removed, transferred to a glass slide in a drop of diluted glycerin or isotonic sodium chloride solution for further studying.

With the settling method, the entire portion of feces being tested must be mixed with water in a glass cylinder or pot, then the top layer of settled liquid must be carefully drained. This is repeated several times. After the liquid becomes clear, it is drained, and the sediment is examined in a glass bath or Petri dish, as indicated above.

Microscopy of stool.

Microscopy is the main method for examining feces to detect helminth eggs and larvae. Stools for analysis should not be delivered

End of work -

This topic belongs to the section:

Biology. Answers to the exam

Biology as one of the theoretical foundations of medicine. development of ideas about the essence of life. molecular biology. basic concepts and terms of genetics. protein synthesis. transcription elongation.

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