Distinctive features and outcomes of infectious diseases. Methods of laboratory research
1. Bacteriocarrier. The ability to long-term survival in the body. infectious process. Infection. Infectious disease.
2. Conditions for the development of infection. Pathogenicity. infectious dose. The rate of reproduction of microorganisms. Entrance gate of an infection. Tropism. Panthropism.
3. Dynamics of the infectious process. bacteremia. Fungemia. Viremia. Parasitemia. Sepsis. Septicemia. Septicopyemia. Toxinemia. Neuroprobasia.
4. Features of infectious diseases. The specificity of the infection. Contagiousness. Infection contagiousness index. Cyclicity. Stages of an infectious disease. periods of infectious disease.
5. Classification (forms) of infectious diseases. exogenous infections. endogenous infections. Regional and generalized infections. Monoinfections. Mixinfections.
6. Superinfections. Reinfections. relapses of infection. Manifest infections. typical infection. atypical infection. chronic infection. Slow infections. persistent infections.
7. Asymptomatic infections. abortion infection. Latent (hidden) infection. Inapparent infections. Dormant infections. Microcarrying.
9. Classification of infectious diseases according to Groboshevsky. population susceptibility. Prevention of infections. Groups of measures for the prevention of infectious diseases.
10. The intensity of the epidemic process. sporadic morbidity. Epidemic. Pandemic. endemic infections. Endemic.
11. Natural focal infections. Parasitologist E.N. Pavlovsky. Classification of natural focal infections. Quarantine (conventional) infections. Especially dangerous infections.
Features of infectious diseases. The specificity of the infection. Contagiousness. Infection contagiousness index. Cyclicity. Stages of an infectious disease. periods of infectious disease.
infectious diseases characterized specificity, contagiousness And cyclicity.
Infection specificity
Every infectious disease causes a specific pathogen. However known infections(for example, purulent-inflammatory processes) caused by various microbes. On the other hand, one pathogen (for example, streptococcus) can cause various lesions.
Contagiousness of an infectious disease. Infection contagiousness index.
contagiousness (infectiousness) determines the ability of the pathogen to be transmitted from one person to another and the rate of its spread in a susceptible population. For a quantitative assessment of contagiousness, it is proposed contagiousness index- the percentage of people who have been ill in a population for a certain period (for example, the incidence of influenza in a certain city for 1 year).
The cycle of an infectious disease
Development of a specific infectious disease limited in time, accompanied by a cyclical process and a change in clinical periods.
Stages of an infectious disease. periods of infectious disease.
Incubation period[from lat. incubatio, lie down, sleep somewhere]. Usually between the penetration of an infectious agent into the body and the manifestation clinical signs There is a certain period of time for each disease - incubation period characteristic only for exogenous infections. During this period, the pathogen multiplies, the accumulation of both the pathogen and the toxins released by it occurs up to a certain threshold value, for which the body begins to respond with clinically pronounced reactions. The duration of the incubation period can vary from hours and days to several years.
prodromal period[from Greek. prodromos running ahead, preceding]. As a rule, the initial clinical manifestations do not carry any pathognomonic [from the Greek. pathos, disease, + gnomon, indicator, sign] for a specific symptom infection. Weakness is common headache, feeling broken. This stage of an infectious disease is called the prodromal period, or "harbinger stage." Its duration does not exceed 24-48 hours.
The period of development of the disease. At this phase, individual features of the disease or signs common to many infectious processes are manifested - fever, inflammatory changes, etc. In the clinically pronounced phase, the stages of an increase in symptoms (stadium wcrementum), the heyday of the disease (stadium acme) and the extinction of manifestations (stadium decrementum) can be distinguished .
convalescence[from lat. re-, repetition of action, + convalescentia, convalescence]. The period of recovery, or convalescence as the final period of an infectious disease, can be fast (crisis) or slow (lysis), and also be characterized by a transition to a chronic state. In favorable cases, clinical manifestations usually disappear faster than the normalization of morphological disorders of organs and tissues and the complete removal of the pathogen from the body. Recovery may be complete or be accompanied by the development of complications (for example, from the side of the central nervous system, musculoskeletal system, or cardiovascular system). The period of final removal of the infectious agent may be prolonged and for some infections (eg, typhoid fever) may be weeks.
The generally accepted term "infectious diseases" was introduced by the German physician Christoph Wilhelm Hufeland. The main signs of infectious diseases:
The presence of a specific pathogen as the direct cause of the disease;
Contagiousness (infectiousness) or the occurrence of several (many) cases of diseases caused by a common source of infection (zoonoses, sapronoses);
Quite often tendency to wide epidemic distribution;
Cyclicity of the course (successive change of periods of the disease);
The possibility of developing exacerbations and relapses, protracted and chronic forms;
Development of immune responses to pathogen antigen;
The possibility of developing carriage of the pathogen.
The higher the contagiousness of the disease, the greater its propensity for widespread epidemic spread. Diseases with the most pronounced contagiousness, characterized by a severe course and high mortality, are grouped especially dangerous infections(plague, smallpox, cholera, yellow fever, Lassa, Ebola, Marburg).
The cyclical flow is characteristic of most infectious diseases. It is expressed in the successive change of certain periods of the disease - incubation (hidden), prodromal (initial), the period of the main manifestations (the height of the disease), the extinction of symptoms (early convalescence) and recovery (reconvalescence).
The incubation (latent) period is the time interval between the moment of infection (penetration of the pathogen into the body) and the appearance of the first clinical symptoms of the disease. The duration of the incubation period is different for different infections and even for individual patients suffering from the same infectious disease (see Annexes, Table 2). It depends on the virulence of the pathogen and its infectious dose, the localization of the entrance gate, the state of the human body before the disease, its immune status. Determination of quarantine terms, holding preventive measures and the solution of many other epidemiological issues is carried out taking into account the duration of the incubation period of an infectious disease.
Prodromal (initial) period. The disease usually lasts no more than 1-2 days, it is not observed in all infections. In the prodromal period, the clinical signs of the disease do not have clear specific manifestations and are often the same in different diseases: fever, headache, myalgia and arthralgia, malaise, fatigue, loss of appetite, etc.
The period of the main manifestations (height) of the disease. It is characterized by the appearance and (often) an increase in the most characteristic clinical and laboratory signs specific to a particular infectious disease. The degree of their severity is maximum in manifest forms of infection. By evaluating these signs, it is possible to make a correct diagnosis, assess the severity of the disease, its immediate prognosis, and the development of emergency conditions.
The different diagnostic significance of the symptoms allows us to subdivide them into decisive, supporting and suggestive.
The decisive symptoms are most characteristic of a specific infectious disease (for example, Filatov-Koplik-Velsky spots in measles, hemorrhagic "star" rash with necrosis elements in meningococcemia).
The supporting symptoms are typical for this disease, but they can also be found
with some others (jaundice with viral hepatitis, meningeal symptoms in meningitis, etc.).
Suggestive symptoms are less specific and similar in a number of infectious diseases.
diseases (fever, headache, chills, etc.).
The period of extinction of symptoms (early convalescence). Follows the peak period with a favorable course of an infectious disease. It is characterized by the gradual disappearance of the main symptoms. One of its first manifestations is a decrease in body temperature. It can happen quickly, over a few hours (crisis), or gradually, over several days of illness (lysis).
The period of recovery (reconvalescence). Develops after the extinction of the main clinical symptoms. Clinical recovery almost always occurs before the morphological disorders caused by the disease completely disappear.
In each case, the duration of the last two periods of an infectious disease is different, which depends on many reasons - the form of the disease and its severity, the effectiveness of the therapy, the characteristics of the immunological response of the patient's body, etc. With complete recovery, all functions impaired due to an infectious disease are restored, with incomplete recovery, certain residual effects remain.
For each patient, the course of an infectious disease has individual characteristics. They may be due to the previous physiological state of the most important organs and systems (pre-healthy background) of the patient, the nature of his nutrition, the features of the formation of nonspecific and specific protective reactions, the presence of previous vaccinations, etc. Numerous environmental factors (temperature, humidity, radiation level, etc.) influence the state of the macroorganism and, consequently, the course of an infectious disease.
Of particular importance in the development of an infectious disease in humans are social factors (population migration, diet, stressful situations, etc.), as well as the adverse effects of a deteriorating environmental situation: radiation, gas pollution, carcinogens, etc. The deterioration of the external environment, most noticeable in recent decades, has an active effect on the variability of microorganisms, as well as on the formation of an unfavorable premorbid background in humans (in particular, immunodeficiency states). As a result, the typical clinical picture and the course of many infectious diseases change significantly. Such concepts as “classic” and “modern” course of an infectious disease, its atypical, abortive, erased forms, exacerbations and relapses have taken root in the practice of infectiologists.
Atypical forms of an infectious disease are considered to be conditions that differ in the dominance in its clinical manifestations of signs that are not characteristic of this disease, or the absence of typical symptoms. An example is the predominance of meningeal symptoms (“meningotifus”) or the absence of roseolous exanthema in typhoid fever. Atypical forms also include an abortive course, characterized by the disappearance of the clinical manifestations of the disease without the development of its most typical signs. With an erased course of the disease, the symptoms characteristic of it are absent, and the general clinical manifestations are mild and short-lived.
An exacerbation of an infectious disease is considered a repeated deterioration in the general condition of the patient with an increase in the most characteristic clinical signs of the disease after their weakening or disappearance. If the main pathognomonic signs of the disease develop again in the patient after the complete disappearance of the clinical manifestations of the disease, they speak of its relapse.
In addition to exacerbations and relapses, complications may develop in any period of an infectious disease. They are conditionally divided into specific (pathogenetically associated with the underlying disease) and nonspecific.
The causative agent of this infectious disease is the culprit of specific complications. They develop due to an unusual severity of typical clinical and morphological manifestations of the disease (for example, acute hepatic encephalopathy in viral hepatitis, perforation of ileal ulcers in typhoid fever) or due to atypical localization of tissue damage (for example, endocarditis or arthritis in salmonellosis).
Complications caused by microorganisms of another species (for example, bacterial pneumonia with influenza) are considered nonspecific.
Most dangerous complications infectious diseases - infectious toxic shock (ITS), acute hepatic encephalopathy, acute kidney failure(ARN), cerebral edema, pulmonary edema, as well as hypovolemic, hemorrhagic and anaphylactic shocks. They are discussed in the corresponding chapters of the special part of the textbook.
Many infectious diseases are characterized by the possibility of developing microbial carriage. Carriage is a peculiar form of the infectious process, in which the macroorganism after the intervention of the pathogen is not able to completely eliminate it, and the microorganism is no longer able to maintain the activity of the infectious disease. The mechanisms of the development of the carrier state have not been sufficiently studied so far, the methods of effective sanitation of chronic carriers have not yet been developed in most cases. It is assumed that the formation of carriage is based on a change in immune responses, in which selective tolerance of immunocompetent cells to pathogen Ag and the inability of mononuclear phagocytes to complete phagocytosis are manifested. The formation of carriage can be facilitated by congenital, genetically determined features of the macroorganism, as well as a weakening of protective reactions due to previous and concomitant diseases, reduced immunogenicity of the pathogen (decrease in its virulence, transformation into L-forms) and other reasons. With the formation \
The prodromal period (the period of precursors of the disease) is characterized by the first symptoms: fever, weakness, depression, loss of appetite. The duration of this period is from several hours to 4 days.
The incubation period is a certain period of time from the moment the microbe enters, until the first clinical signs of the disease appear. With different infectious diseases, it is not the same: from several days, months to several years.
Characteristic features of an infectious disease
infectious disease- has a number of features that distinguish it from non-infectious diseases.
Features of an infectious disease:
I. An infectious disease is caused by a certain specific pathogen.
II. The diseased organism itself becomes a source of the infectious agent, which is released from the diseased organism and infects healthy animals, i.e. Infectious diseases are characterized by contagiousness, microbe carrying.
III. In a diseased organism, the processes of formation of specific antibodies take place, as a result of which the organism, after recovery, in most cases becomes immune, i.e. immune to re-infection with the same pathogen.
The infectious process can be asymptomatic, covert, latent (latent infection). Consequence latent infection May be immunizing subinfection- a state when pathogenic microbes enter the animal's body in small doses and repeatedly, cause immunobiological reactions, the production of antibodies, but they themselves die. These animals do not show functional disorders, and after slaughter they do not detect pathological changes in organs and tissues. Asymptomatic infection- invisible, inapparate, not manifested. dormant infection- latent, not manifested clinically. It is determined using allergic, immunobiological reactions, microbiological, virological and pathomorphological studies. It often happens with brucellosis, tuberculosis, glanders, paratuberculosis, etc.
The infectious process is characterized by cyclical development and includes the following periods:
1. Incubation.
2. Prodromal.
3. Clinical (the height of the disease).
4. Recovery (convalescence).
The period of development of the main clinical signs (the period of the peak of the disease)- the main signs characteristic of this infectious disease appear (with foot-and-mouth disease - aphthae, with rabies - paralysis, with botulism - muscle relaxation), depression, heat, violation of breathing, digestion, etc.
This period is changing recovery period (reconvalescence) - are gradually recovering physiological functions organism. Clinical recovery in many infectious diseases does not coincide in time with the release of the body from the pathogen. After recovering from an infectious disease, in some cases, as a result of the formation of immunity, the body is completely freed from the pathogen, in some cases, after recovery, the pathogen remains in the body of animals for a long time. This condition is called microbe or virus carrier (salmonellosis, pasteurellosis, tuberculosis, etc.). Such animals are dangerous as a source of infectious agents. There is a microcarrier that is not associated with a previous illness, it is not accompanied by immunological restructuring and is detected only by bacteriological examination. This state is natural for conditionally pathogenic microflora, until its activation. For example, resistant animals can be carriers of Salmonella, Pasteurella, swine erysipelas, etc. There may be a short-term carriage of a pathogen that is unusual for animals of this species, such as the INAN virus in pigs, the swine mind virus in dogs. Such animals can serve as a source of infectious agents.
The course of an infectious disease can be fulminant, acute subacute, chronic, abortive, and the form of clinical manifestation can be typical and atypical. Forms of manifestation of the disease are characterized on the basis of predominant localization pathological process(intestinal, pulmonary and cutaneous forms of anthrax).
For acute course illness, usually lasting from one to several days, is characterized by a rapid manifestation of typical clinical signs. This is how they can run anthrax, foot and mouth disease, emkar, rabies.
A hyperacute (fulminant) course is possible, in which the animal dies after a few hours, due to rapidly developing sepsis or toxemia (anthrax, infectious enterotoxemia and sheep brazil). Typical clinical signs in such cases do not have time to develop.
With a subacute, longer course, the clinical signs of the disease are also typical, but less pronounced. However, pathological changes are characteristic. In outbreaks of erysipelas or classical swine fever, for example, both acute and subacute course of the disease is noted, which is explained by differences in the resistance of animals and the virulence of the pathogen.
In a chronic course, the disease can drag on for months, and even years. Clinical signs are weakly expressed, and sometimes absent at all (with infectious anemia of horses, tuberculosis, brucellosis, glanders), which makes it difficult to diagnose the disease. The disease can take such a course with a decrease in the virulence of the pathogen and a sufficiently high resistance of the animal.
Transitions from one type of disease to another are not excluded. So, with erysipelas of pigs, the outcome of an acute or subacute course of the disease can be chronic infection. There are also exacerbations of chronic diseases.
If a complex of clinical signs is characteristic of a given infectious disease, then the form of its manifestation is characterized as typical. However, deviations from the typical picture are not uncommon due to mild illness (anginous anthrax in pigs). Such forms of manifestation of the disease are considered atypical. In such cases, the incompleteness of the clinical picture and the blurring of clinical signs make it difficult to diagnose. IN last years cases of atypical manifestations of infectious diseases (CSF, Newcastle disease of chickens, rabies and many others) have become noticeably more frequent. This is associated with changes in the biological activity of pathogens, with mass vaccination, with widespread (often asymptomatic) use medicines and especially antibiotics.
An atypical manifestation of diseases in malnourished animals due to the suppression of their immunobiological reactivity is not excluded. If the infectious process quickly ends with the recovery of the animal, then the course of the disease is called benign. But with a reduced resistance of the animal, the disease can take a malignant course, characterized by high mortality. Such a more severe, complicated form of the manifestation of the disease should also be considered atypical.
If the typical development of the disease suddenly stops (breaks off) and recovery occurs, the course of the disease is called abortive. Abortive disease is short-term, manifested in mild form in the absence of some, often the main clinical signs. The reason for this flow is considered to be the high resistance of the animal. The abortive course of smallpox in coarse-wooled sheep is known, when the papules (nodules) formed on the skin quickly disappear, and the general condition of the animals remains satisfactory. The abortive course of myta in horses is characterized by a short-term fever and a slight increase in lymph nodes without suppuration. If, after suffering an infectious disease and the release of the animal's body from its pathogen, re-infection occurs with the same type (serotype) of a pathogenic microbe, reinfection occurs. The main condition for its development is the preservation of susceptibility to this pathogen (absence or insufficient strength of immunity). Superinfection is also possible - as a result of (re)infection, which occurred against the background of an already developed infection caused by the same type of pathogenic microbe. A new infection that occurred before the release of the animal's body from the pathogen usually aggravates the disease, exacerbates its course. The return of an infectious disease, the reappearance of its symptoms after clinical recovery is called a relapse. It occurs as an endogenous reinfection with a decrease in the resistance of the animal and the activation of the causative agent of the disease that has survived in the body. Relapses are characteristic of diseases in which insufficiently strong immunity is formed. The infectious process is very often asymptomatic, hidden, latent (asymptomatic or latent infection). An immunizing subinfection should be considered a peculiar form of latent infection - this is a phenomenon when pathogenic microbes that repeatedly enter the animal's body in small doses cause immunobiological reactions, the production of specific antibodies, but they themselves die. Accordingly, the animal does not become a source of the pathogen, pathomorphological changes are not detected, functional disorders are not detected. This condition can be caused by pathogens of emphysematous carbuncle, leptospirosis, and other infectious diseases.
For the emergence of an infectious disease, conditions are necessary: first, the microbe must be sufficiently virulent; secondly, it is necessary to introduce a certain number of microbes; thirdly, they must enter the body through the gates of infection that are favorable for them and reach susceptible tissues; fourthly, the host organism must be susceptible to this pathogen; fifthly, certain environmental conditions are necessary under which the interaction between the microbe and the organism occurs.
Any infection begins with the attachment of the surface antigenic structures of the pathogen to the receptors of the host cells. The ability of pathogenic microorganisms to penetrate into the internal environment of the host, overcome protective barriers, and spread in the body is called invasiveness. This ability is associated with the production of enzymes (hyaluronidase, fibrinolysin, collagenase) that violate the integrity of some tissues and the presence of aggressins - substances that inhibit phagocytosis and bacteriolysis. Aggressins are part of the cell wall and capsule of many pathogenic microbes.
Serological studies are based on a specific reaction between antigens and antibodies.
Antigens- genetically alien substances, when introduced into the body of an animal (and a person), cause a response (antigenic property) in the form of the production of protective bodies - antibodies specific to the antigen. Antigenic substances are macromolecular compounds with certain properties: foreignness, antigenicity, immunogenicity, specificity, colloidal structure and a certain molecular weight. Antigens can be a variety of protein substances, as well as proteins in combination with lipids and polysaccharides. Animal cells have antigenic properties plant origin, animal poisons (snakes, scorpions, bees, etc.) and plant poisons (ricin, cortin, etc.), complex complexes consisting of polysaccharides, lipids, proteins. Viruses, bacteria, microscopic fungi, protozoa, exo- and endotoxins of microorganisms have antigenic properties. There are corpuscular, cellular (bacteria, erythrocytes) and soluble (molecularly dispersed) antigens. Antigens are polyvalent - they have several determinant receptors for binding to antibodies (antigenic function) both in the animal body (in vivo) and outside the body - in vitro (in vitro). The antigenic function is possessed not only by complete antigens, but also by inferior ones (haptens), that is, substances non-protein nature(polysaccharides, lipid-polysaccharide complex of the somatic antigen of a microbial cell, and other substances).
Antigenicity refers to the ability of an antigen to elicit an immune response. The degree of the body's immune response to a different antigen will not be the same, that is, an unequal amount of antibodies will be produced for each antigen.
Immunogenicity is the ability to create immunity. This concept refers mainly to viral and microbial antigens that provide the creation of immunity to infectious diseases. To be immunogenic, an antigen must be foreign to a given recipient, have a molecular weight of at least 10,000. Immunogenicity increases with increasing molecular weight. Corpuscular antigens (bacteria, fungi, protozoa, erythrocytes) are more immunogenic than soluble ones, and among the latter, high molecular weight, for example, aggregated, antigens are more immunogenic.
Specificity is a feature of the structure of substances by which antigens differ from each other. It is determined by the antigenic determinant, that is, a small section of the antigen molecule, which combines with the antibody developed against it. The number of such sites (groups) is different for each antigen and determines the number of antibody molecules with which the antigen can combine (valency). The valency of the antigen depends on the number of determinants: the larger the molecule, the higher the valence.
Antigens are divided into complete and defective. Full-fledged antigens cause the synthesis of antibodies or sensitization in the body (sensitization is the acquisition by the body of a specific hypersensitivity to foreign substances, often of a protein nature, allergens) of lymphocytes, and react with them both in vivo and in vitro. Full-fledged antigens are characterized by strict specificity, i.e., they cause in the body the production of only specific antibodies that react only with this antigen.
Incomplete antigens, or haptens, are complex carbohydrates, lipids and other substances that are not capable of causing the formation of antibodies, but enter into a specific reaction with them. The addition of small amounts of protein to haptens gives them the properties of full-fledged antigens. The protein that enlarges the hapten molecule is called "schlepper"(German schlepper - conductor). Forsman's heterogeneous antigens are also haptens, which were described in
1911 Forsman showed that in the organs of animals different types(cats, dogs, horses, chickens, guinea pigs, etc.) contains a common antigen, but is absent in humans, monkeys, rabbits, ducks and rats. This is a lipoid fraction that has the properties of a hapten.
conjugated antigens. This term refers to proteins that have acquired a new antigenic specificity due to the addition of a new chemical group to them using a chemical bond.
Antigens of animal origin are divided by specificity into species, group, organ and stage-specific.
species specificity. Animals of different species have antigens characteristic only of this species, which is used in determining the falsification of meat, blood groups by using anti-species sera.
Group specificity characterizes the antigenic differences of animals in terms of erythrocyte polysaccharides, blood serum proteins, surface antigens of nuclear somatic cells. Antigens that cause intraspecific differences between individuals or groups of individuals are called isoantigens, for example, group human erythrocyte antigens. Organ (tissue) specificity is characterized by unequal antigenicity of different organs of the animal, for example, the liver, kidney, spleen differ in antigens. Stage-specific antigens arise in the process of embryogenesis and characterize a certain stage in the intrauterine development of an animal, its individual parenchymal organs.
Autoantigens. In some cases, the proteins of their own tissues (heart, liver, kidneys, etc.) when combined with the protein of microorganisms, toxins or enzymes of bacteria, medicinal substances, under the influence of physical factors (burn, radiation, frostbite) change their physical and chemical properties and become alien to the body - autoantigens. The body produces antibodies against these antigens, causing autoimmune diseases.
Antigens of microorganisms. Viruses, bacteria, fungi and their separate structures, exo- and endotoxins have the property of full-fledged antigens.
There are antigens common to related species, which are designated as species and group antigens, and type-specific antigens, characteristic of a particular type (variant). Since viruses are complex antigens, some of which are associated with the antigens of the outer shell of the virus, some with the internal nucleoprotein, antiviral antibodies also have pronounced heterogeneity with a wide range antibodies.
Antibodies- These are specific proteins - immunoglobulins, which are formed in the body by plasma cells under the influence of an antigen and have the ability to specifically bind to it. Antibodies are formed in the body as a result of natural infection, after the introduction of live or killed vaccines, upon contact of the lymphoid system with foreign cells and tissues. Antibodies according to their functional properties are divided into neutralizing, lysing and coagulating. Neutralizing agents include antitoxins, antienzymes, virus-neutralizing, lysine antibodies; to coagulating - agglutinins and lysing precipitins - bacteriolysins, hemolysins, complement-fixing antibodies have been isolated.
Taking into account the functional ability of antibodies, serological reactions of agglutination, hemolysis, lysis, precipitation, etc. were named. in an electric field, blood serum proteins are divided into albumins and three globulin fractions: α, β, γ. During electrophoresis, it was found that antibodies are present only in β- and γ-fractions. By high-speed centrifugation, antibodies were divided into two main groups: 7S (sedimentation - sedimentation rate) - small molecules and 19S - large molecules, with 7S found in γ-globulins, and 19S - in β-globulins. Antibodies have a different number of active centers in the molecule, this determines their valency. Antibodies are divided into complete and incomplete. Complete antibodies, when interacting with an antigen, give visible reactions (agglutination, lysis, precipitation, etc.), incomplete antibodies, after interaction with a specific antigen, do not give a visible manifestation serological reactions. When an antigen is introduced into the body, antibodies with different functional activity are formed (pricipitins, agglutinins, lysines, etc.). they are all identical, their action is different, there are at least 10,000 of these antibodies.
According to the International Classification, antibodies are called immunoglobulins and are designated Ig. Immunoglobulins are proteins with a quaternary structure, that is, their molecules are built from several polypeptide chains. The molecule of each class consists of two identical heavy (H) and two identical light (L) chains linked by non-covalent interactions, disulfide bridges and a tail. Light chains are common to all classes and subclasses. Heavy chains have characteristic structural features for each class (subclass). Light chains are divided into two types: K (Kappa) and l (Lambda). Heavy chains are denoted by Greek letters: g (Gamma), m (Mu), a (alpha), d (delta), e (epsilon) - according to the Latin designation of a particular class of immunoglobulins: IgG, IgM, IgA, IgD, IgE. At the end of each of the two “branches” there are two identical antigen-binding sites (because of this, antibodies are called bivalent), with the help of which antibodies sew antigen molecules into an extensive network, since each antigen molecule has three or more antigenic determinants. The efficiency of antigen binding and cross-linking reactions with antibodies is significantly increased due to the flexible hinge section at the junction of both "branches" with the "tail".
Infectious diseases are diseases caused by pathogenic microorganisms. A person is infected with these diseases from another person or from animals, birds, fish.
Infectious diseases can be single and massive. Rapidly spreading diseases affecting a large number of people cause epidemics. Epidemics that span multiple continents are called pandemics.
Infectious diseases are characterized by the possibility of infection, a tendency to spread, in most cases, the cyclical nature of diseases, and the formation of immunity. Sometimes patients can remain carriers of the infection, or the disease can become chronic.
Infectious diseases are treated with specific therapeutic agents that act on pathogens. These are chemicals, antibiotics, serums, etc. For the course of the disease, the water-salt balance, appropriate nutrition of the patient and care are of great importance. Immunization is widely used to prevent infectious diseases.
Infectious diseases are divided into 4 groups:
1. intestinal,
2. respiratory tract,
3. blood,
4. skin.
Intestinal infections spread with contaminated feces water, food, contaminated hands (Fig. 68). This group includes: food poisoning, dysentery, typhoid fever, cholera.
In the case of skin infections, the pathogen penetrates through damage to the skin (skin, mucous membranes) or damaged soft tissues. This group of infections includes tetanus, erysipelas, anthrax, etc.
All persons contracting or suspected of having a communicable disease should be isolated on board to prevent the spread of the disease. It should be remembered that every patient suffering from diarrhea may be a carrier of infection. To block the spread of infection, it is very important to properly disinfect the patient's secretions, his belongings, and the premises.