Infection is a state of contamination that occurs as a result of the penetration of substances into the macroorganism.

The infectious process is the dynamics of interaction between micro- and macroorganisms.

If the pathogen and the animal’s body (host) meet, this almost always leads to an infection or an infectious process, but not always to an infectious disease with its clinical manifestations. Thus, the concepts of infection and infectious disease are not identical (the first is much broader).

Forms of infection:

Overt infection or infectious disease– the most striking, clinically pronounced form of infection. The pathological process is characterized by certain clinical and pathological signs.

Hidden infection(asymptomatic, latent) – the infectious process does not manifest itself externally (clinically). But the infectious agent does not disappear from the body, but remains in it, sometimes in an altered form (L-form), retaining the ability to be restored to a bacterial form with its inherent properties.

Immunizing subinfection – the pathogen that enters the body causes specific immune reactions, dies or is eliminated; the body does not become a source of infectious agents, and functional disorders do not appear.

Microcarrier – The infectious agent is present in the body of a clinically healthy animal. Macro- and microorganism are in a state of some equilibrium.

2. Characteristics of infectious diseases

1. Etiology (each infectious disease is caused by a specific pathogen).

2. Contagiousness (contagiousness, infectiousness).

3. Epidemic (tendency to spread). Can be:

· sporadic diseases - isolated cases of disease in a given region;

· epidemics - outbreaks of disease of various sizes;

Pandemic - a disease spreads over large areas.

4.specificity of localization in certain organs and tissues.

5. Specificity of transmission mechanisms

6. repeatability or non-repeatability (as a result of immunity.)

7. Cyclicity of the course (i.e. the presence of certain periods of the disease).

3. Pathogenicity and virulence of bacteria. Pathogenicity factors.

Virulence is a property of a strain that manifests itself under certain conditions (with variability of microorganisms, changes in the susceptibility of the macroorganism, etc.)

Pathogenicity factors include:

adhesion - the ability of microorganisms to attach to cells

colonization – the ability to settle on the surface of microorganisms

invasion – the ability to penetrate the cells of microorganisms

aggression - the ability to resist the body's defense factors

4. Fundamentals of the epidemiology of infectious diseases. Epidemic process.Epidemic process - the process of emergence and spread of a specific infectious condition among the population. Elements of the epidemic process: 1. Source of infection (animals, humans, objects environment contaminated with human or animal excretions or employees natural environment habitat of some pathogenic microorganisms) 2. Mechanisms, routes and factors of transmission of infection (fecal-oral, respiratory, blood, contact, vertical (from mother to child)) 3. Community susceptibility When 95% of immunological resistance is reached, the circulation of the pathogen in the community stops (mass mass vaccination against certain pathogens). The intensity of the epidemic process. Expressed in morbidity and mortality rates per 10 or 100 thousand population, indicating the name of the disease, territory and historical period of time. There are three levels: - pandemic - epidemic - periodic morbidity

5. Main sources of infectious diseases. Animals, humans, environmental objects contaminated with animal and human secretions or serving as a natural habitat for pathogenic microorganisms. Infections: -anthroponotic (only people get sick) -zoonotic -zooanthroponotic are characterized by natural focality (the constant presence of a sick animal, environmental factors that ensure transmission of the pathogen, carriers of infection) -sapronotic (normal inhabitants of the environment)

6. Mechanisms, routes and factors of transmission of infection. 1. Fecal-oral Paths: aquatic, food (alimentary) Factors: food, water, items. 2. Aerogenic (respiratory) Paths: airborne, airborne dust Factors: dust, cough. 3. Blood (transmissible) Paths: blood-sucking insect bites, surgical interventions, sexual intercourse Factors: blood. 4. Contact Paths: wound, genital, direct contact 5. Vertical Paths: transplacental Factors: from mother to child.

Infection(infectio - infection) - the process of penetration of a microorganism into a macroorganism and its reproduction in it.

Infectious process– the process of interaction between a microorganism and the human body.

The infectious process has various manifestations: from asymptomatic carriage to infectious disease (with recovery or death).

Infectious disease- this is the extreme form infectious process.

An infectious disease is characterized by:

1) Availability certain live pathogen ;

2) contagiousness , i.e. pathogens can be transmitted from a sick person to healthy ones, which leads to widespread spread of the disease;

3) the presence of a certain incubation period And characteristic sequential change periods during the course of the disease (incubation, prodromal, manifest (the height of the disease), revalescence (recovery));

4) development characteristic of of this disease clinical symptoms ;

5) availability immune response (more or less long-lasting immunity after illness, development allergic reactions in the presence of a pathogen in the body, etc.)

The names of infectious diseases are formed from the name of the pathogen (species, genus, family) with the addition of the suffixes “oz” or “az” (salmonellosis, rickettsiosis, amoebiasis, etc.).

Development infectious process depends:

1) on the properties of the pathogen ;

2) on the state of the macroorganism ;

3) depending on environmental conditions , which can affect both the state of the pathogen and the state of the macroorganism.

Properties of pathogens.

The causative agents are viruses, bacteria, fungi, protozoa, helminths (their penetration is invasion).

Microorganisms that can cause infectious diseases are called pathogenic , i.e. pathogenic (pathos - suffering, genos - birth).

There are also opportunistic microorganisms that cause diseases when sharp decline local and general immunity.

Pathogens infectious diseases have properties pathogenicity And virulence .

Pathogenicity and virulence.

Pathogenicity– this is the ability of microorganisms to penetrate a macroorganism (infectivity), take root in the body, multiply and cause a complex of pathological changes (disturbances) in organisms sensitive to them (pathogenicity – the ability to cause an infectious process). Pathogenicity is a species-specific, genetically determined trait or genotypic trait.

The degree of pathogenicity is determined by the concept virulence. Virulence is a quantitative expression or pathogenicity. Virulence is phenotypic trait. This is a property of a strain that manifests itself under certain conditions (with variability of microorganisms, changes in the susceptibility of the macroorganism).

Quantitative indicators of virulence :

1) DLM(Dosis letalis minima) – minimum lethal dose– the minimum number of microbial cells that causes the death of 95% of susceptible animals under given specific experimental conditions (type of animal, weight, age, method of infection, time of death).

2) LD 50 – the amount that causes the death of 50% of experimental animals.

Since virulence is a phenotypic trait, it changes under the influence of natural causes. It can also be artificially change (up or down). Promotion carried out by repeated passaging through the body of susceptible animals. Demotion - as a result of exposure to unfavorable factors: a) heat; b) antimicrobial and disinfectants; c) growing on unfavorable nutrient media; d) defenses of the body - passage of slightly susceptible or unresponsive animals through the body. Microorganisms with weakened virulence are used to obtain live vaccines.

Pathogenic microorganisms also have specificity, organotropy and toxicity.

Specificity– ability to cause certain infectious disease. Vibrio cholerae causes cholera, Mycobacterium tuberculosis causes tuberculosis, etc.

Organotropy– the ability to infect certain organs or tissues (the causative agent of dysentery is the mucous membrane of the large intestine, the influenza virus is the mucous membrane of the upper respiratory tract, rabies virus - nerve cells Ammon's horn). There are microorganisms that can infect any tissue, any organ (staphylococci).

Toxicity– ability to form toxic substances. Toxic and virulent properties are closely related.

Virulence factors.

The characteristics that determine pathogenicity and virulence are called virulence factors. These include certain morphological(presence of certain structures - capsules, cell wall), physiological and biochemical signs(production of enzymes, metabolites, toxins that have an adverse effect on the macroorganism), etc. By the presence of virulence factors, pathogenic microorganisms can be distinguished from non-pathogenic ones.

Virulence factors include:

1) adhesins (provide adhesion) – specific chemical groups on the surface of microbes, which, like a “key to a lock,” correspond to the receptors of sensitive cells and are responsible for the specific adhesion of the pathogen to the cells of the macroorganism;

2) capsule – protection against phagocytosis and antibodies; bacteria surrounded by a capsule are more resistant to the action of the protective forces of the macroorganism and cause a more severe course of infection (pathogens of anthrax, plague, pneumococci);

3) surface-located substances of the capsule or cell wall of various natures (surface antigens): protein A of staphylococcus, protein M of streptococcus, Vi-antigen of typhoid bacilli, lipoproteins of gram “-” bacteria; they perform the functions of immune suppression and nonspecific protective factors;

4) aggression enzymes: proteases, destroying antibodies; coagulase, blood plasma clotting; fibrinolysin, dissolving fibrin clots; lecithinase, destroying lecithin membranes; collagenase, which destroys collagen; hyaluronidase, destructive hyaluronic acid intercellular substance of connective tissue; neuraminidase, destroying neuraminic acid. Hyaluronidase , breaking down hyaluronic acid, increases permeability mucous membranes and connective tissue;

toxins - microbial poisons - powerful factors of aggression.

Virulence factors provide:

1) adhesion – attachment or adhesion of microbial cells to the surface of sensitive cells of the macroorganism (to the surface of the epithelium);

2) colonization – reproduction on the surface of sensitive cells;

3) penetration – the ability of some pathogens to penetrate (penetrate) inside cells - epithelial, leukocytes, lymphocytes (all viruses, some types of bacteria: Shigella, Escherichia); in this case, the cells die, and the integrity of the epithelial cover may be disrupted;

4) invasion – the ability to penetrate through mucous and connective tissue barriers into underlying tissues (due to the production of the enzymes hyaluronidase, neuraminidase);

5) aggression - the ability of pathogens to suppress nonspecific and immune defenses of the host body and cause the development of damage.

Toxins.

Toxins are poisons of microbial, plant or animal origin. They have a high molecular weight and cause the formation of antibodies.

Toxins are divided into 2 groups: endotoxins and exotoxins.

Exotoxinsstand out into the environment during the life of a microorganism. Endotoxins tightly bound to the bacterial cell and stand out into the environment after cell death.

Properties of endo and exotoxins.

Exotoxins	Endotoxins
	Lipopolysaccharides
Heat labile (inactivated at 58-60°C)	Thermally stable (withstands 80 - 100С)
Highly toxic	Less toxic
Specific	Non-specific ( general action)
High antigenic activity (causes the formation of antibodies - antitoxins)	Weak antigens
Under the influence of formalin they turn into toxoids (loss of poisonous properties, preservation of immunogenicity)	Partially neutralized by formaldehyde
Formed mainly by gram “+” bacteria	Formed mainly by gram “-” bacteria

Exotoxins form the causative agents of the so-called toxinemic infections, which include diftheria, tetanus, gas gangrene, botulism, some forms of staphylococcal and streptococcal infections.

Some bacteria simultaneously produce both exo- and endotoxins (Escherichia coli, Vibrio cholerae).

Obtaining exotoxins.

1) growing a toxigenic (exotoxin-forming) culture in a liquid nutrient medium;

2)filtration through bacterial filters (separation of exotoxin from bacterial cells); Other cleaning methods can be used.

Exotoxins are then used to produce toxoids.

Obtaining toxoids.

1) 0.4% formalin is added to the exotoxin solution (filtrate of a broth culture of toxigenic bacteria) and kept in a thermostat at 39-40°C for 3-4 weeks; there is a loss of toxicity, but the antigenic and immunogenic properties are preserved;

2) add a preservative and adjuvant.

Anatoxins These are molecular vaccines. They are used for specific prevention of toxinemic infections , and to obtain therapeutic and prophylactic antitoxic serums, also used for toxinemic infections.

Obtaining endotoxins.

Various methods are used destruction of microbial cells , and then carry out cleaning, i.e. separation of endotoxin from other cell components.

Since endotoxins are lipopolysaccharides, they can be extracted from the microbial cell by destroying it with TCA (trichloroacetic acid) followed by dialysis to remove proteins.

There is no doubt that “infection”, “infectious process” and “infectious disease” are in a certain way associated with pathogenic microbes and at the same time with a macroorganism (human, animal, etc.). It can be noted that pathogenic microbes located in the external environment are not yet an infection, because they can significantly change their metabolism and lose some of the pathogenic factors (spores). Microflora of the human body that does not cause pathological process, is also not an infection and quite mutually beneficial processes often “start” between it and the body.

The term “infection” in translation means “I infect”, “I pollute” and is more closely associated with pathogenic microorganisms that are not in a dormant state or outside the human body, but in opposition to the macroorganism. Pathogenic microorganisms do not interact with the human body, and both of these sides, being in opposition, try to break each other’s resistance.

Thus, infection is a general term indicating microorganisms that exhibit their inherent degree of pathogenicity in a susceptible human body and cause an infectious process, highest form the manifestation of which is an infectious disease.

This reflects the essence of the infectious process and infectious disease, as well as the factors involved in them. This fully corresponds to the term “source of infection” in relation to patients with an obvious or latent infectious process, which are isolated in external environment pathogenic microbes that, through a wide variety of contacts, can cause this disease in other susceptible people.

Known different variants infection of people with an infectious principle, which is determined for various reasons:

1. Superinfection- layering of repeated infection, which can again cause an infectious disease of identical etiology in a sick person. This option is possible in the absence of immunity (gonorrhea and other infections)

2. Reinfection- layering of repeated infection, which causes an infectious disease of identical etiology in the person who has been ill. The option is similar to the previous one.

3. Secondary infection- layering new infection, which causes a disease of a different etiology in the patient against the background of primary infectious disease.

4. Autoinfection- this is one’s own infection (formerly opportunistic, opportunistic microflora), which caused a weakened person (hypothermia, vitamin deficiency, acute and chronic diseases, stress, etc.) infectious disease.

5. Mixed infections- these are polyinfections that cause a polyetiological infectious disease in a susceptible person.

6. Monoinfection– an infection of one species that causes in a susceptible person a monoinfectious disease characteristic of that species.

By origin, the infection can be exogenous or endogenous.

Exogenous infection- these are pathogenic microbes that have penetrated into a susceptible organism from the external environment (soil, water, food, toys, hands, air, medications, etc.), through numerous factors and routes of infection..

Endogenous infection- this is the microflora of the human body, which he normally does not notice, but it can cause certain infectious diseases when the body’s defenses are weakened, the skin and mucous membranes are damaged, etc.

If the name of a disease or type of bacteria is added to the term “infection,” a more specific infectious agent or causative agent of an infectious disease or group of such diseases will appear, e.g. intestinal infection, typhoid infection, etc.

The process of infection entering the body of a susceptible person, in general, can be described as infection, i.e. a process that combines stages referred to as adhesion, colonization and invasion. If pathogenic microorganisms enter environmental objects and contaminate them, then this process is called microbial contamination or contamination.

The infectious process is a complex of multi-level and multi-system internal processes, including pathological ones, occurring in the body in response to the pathogenic effects of infection. The accumulation of internal processes often turns into pathology, which is manifested by manifest (external) signs. This indicates the occurrence of an infectious disease. It happens that internal processes, reflecting the degree of the body’s resistance to infection, do not develop into a manifest form, although the duration of the internal process can be significant (for example, persistence, etc.).

Thus, an infectious disease is a manifest manifestation of an infectious process occurring in the body in response to the pathogenic effects of an infection, which can be exogenous or endogenous in origin.

Due to predominant disease people or animals, the following main groups of infectious diseases are distinguished:

n anthroponotic(mostly people get sick, for example, cholera, typhoid fever, gonorrhea, etc.),

n zoonotic(mainly animals suffer, for example, swine fever, chicken cholera, infectious anemia horses, etc.)

n anthropozoonotic(people and animals are sick, for example, tularemia, leptospirosis, plague, brucellosis, etc.).

At the same time, such gradations are quite arbitrary, generated by the level of knowledge modern science. For example, shigellosis (dysentery) for a long time were considered an anthroponotic disease, but at present significant data have accumulated on the disease of shigellosis in cows, pigs and other animals and birds with clinical picture and the release of Shigella. Some types of viruses that previously affected monkeys now cause diseases in humans (HIV, Ebola, etc.).

Forms of symbiosis between macro- and microorganisms.

Mutualism - mutually beneficial cohabitation.

Commensalism - one organism lives at the expense of another, without causing harm to the latter.

Infection and infectious process. If the pathogen and the animal’s body (host) meet, this almost always leads to an infection or an infectious process, but not always to an infectious disease with its clinical manifestations. Thus, the concepts of infection and infectious disease are not identical (the first is much broader).

Infectious process - This the interaction of the pathogen and the individual animal is the smallest unit of the epizootic process, just its initial stage. First, an infectious process develops, and then, in the presence of additional mechanisms (factors), an epizootic process. The infection is characterized by four main forms.

Forms of infection.

Clear infection and - the most striking, clinically pronounced form of infection.

Infectious disease - p The pathological process is characterized by certain clinical and pathological signs.

Hidden infection(asymptomatic, latent, dormant, undetectable, innaparent) - the infectious process does not appear externally.

Immunizing subinfection - a pathogen that enters the body causes specific immune reactions, itself dies or is excreted; the body does not become a source of infectious agents, and functional disorders do not appear. This form can only be detected using immunological reactions (it is widespread in nature, and its causes are not fully understood).

Microcarrier. : healthy (transient); convalescents; immune (non-sterile immunity) - the infectious agent is present in the body of a clinically healthy animal. Macro- and microorganism are in a state of some equilibrium. Microcarriers are hidden sources of infectious agents .

Infectious disease is one of the forms of infection and is characterized by six main symptoms:

Specificity - the presence of certain pathogens in the macroorganism; contagiousness (contagiousness, lat. contagiosys - contagious) - the ability of the pathogen to be released from organs and tissues and infect new susceptible animals;

The presence of a latent (incubation) period;

Cyclicity - sequential change of certain periods of illness; -----

Specific responses of the macroorganism (mainly immunological, etc.); lesions and a tendency for mass to wide territorial distribution (not noted for all diseases).

Hidden (latent) infection, flowing without visible signs, is a fairly common phenomenon. In this case, the infectious agent does not disappear from the body, but remains in it, sometimes in an altered form (L-form), retaining the ability to revert into a bacterial form with its inherent properties.

Microcarrier- does not equate to latent infection. In the case of the latter, it is possible to determine the periods (dynamics) of the infectious process, that is, its occurrence, course and extinction, as well as the development of immunological reactions. This cannot be done with microbial carriage.

There are also microorganisms that cause an infectious process only under certain conditions. For them, a not entirely correct term has taken root in science - optional (conditional) pathogenic microorganisms .

The pathogenic effect is characterized by specificity: each type pathogenic microorganisms when it enters the body in a quantity sufficient for infection - an infectious dose - it causes a certain infection (with so-called classical monoinfections). This specificity is very strict, and therefore the classification of diseases is based on the principle: 1 pathogen - 1 disease.

Pathogenicity is a genetic trait, a qualitative characteristic of a species, fixed in its hereditary (chromosomal) apparatus. Most pathogens are obligate pathogenic: their ability to cause an infectious process is a constant species characteristic .

At the same time, in different groups of the same type of microorganism (strains or serotypes), under the influence of various factors, pathogenicity can vary significantly. Virulence - degree, or measure, of pathogenicity; is a phenotypic, individual characteristic of a strain, which can vary significantly - avirulence increases, decreases, or is completely lost.

Pathogenicity factors.

Each pathogenic microorganism is characterized by a specific set of pathogenicity factors, which are very diverse. First of all, it should be noted invasiveness(aggressiveness) - the ability of a microorganism to penetrate natural barriers and multiply in tissues and toxicogenicity - the ability to secrete toxins (poisons). Pathogenicity factors also include: exotoxins- the most powerful known biological and chemical poisons.

Exo- and endotoxins.

toxins (poisons). Pathogenicity factors also include:

exotoxins- are released into the environment, are thermolabile (low-stable), act slowly; are proteins produced, as a rule, by gram-positive bacteria (staphylococci, streptococci, clostridia);

endotoxins - are mainly lipopolysaccharides produced by gram-negative bacteria (brucella, salmonella, mycobacteria); strongly associated with the bacterial cell (released when it is destroyed), thermostable, and act quickly.

enzymes (enzymes).- hyaluronidase, fibrinolysin, coagulase, collagenase, streptokinase, lecithinase, deoxyribonuclease, protease, decarboxylase, etc.; act strictly selectively, they have the properties of distribution factors (permeability, invasiveness); polysaccharides (O-antigens) - somatic (envelope) antigen of some gram-negative bacteria (Escherichia, Salmonella, Brucella);

Development of the infectious process: determined by specific general and local action pathogen and a complex of responses of the macroorganism. Great importance in the process of infection of the body and reproduction of the pathogen in it, there is a mechanism for the penetration of the pathogen into the body (infection).

THE IMPORTANCE OF MICRO- AND MACRORGANISM IN THE FORMATION OF INFECTION.

Etiological factor (etiological agent) of infectious diseases - a pathogenic microorganism, also called the causative agent of the disease. The breadth of the pathogenic spectrum of microorganisms (the ability to cause disease in one, several or many species of animals) can vary significantly.

Pathogens that are pathogenic to one species of animal are called monophages(swine fever virus, sheep pox, equine infectious anemia, rabbit myxomatosis, etc.); pathogens pathogenic for many species - polyphages(rabies virus, pathogens of tuberculosis, brucellosis, salmonellosis, colibacillosis, etc.). The occurrence, course and form of infection depend not only on the virulence and number of microorganisms that have entered the body, but also on the susceptibility or resistance of the animal’s body. Body susceptibility - the ability of an animal to become infected and become ill with an infectious disease. In Susceptibility is genetically fixed at the level of the animal species (for example: glanders, myt, equine infectious anemia, myxomatosis.

Susceptibility is affected by:

Environmental factors

- stressors(extraordinary irritants): chemical, feed, traumatic, transport, technological, biological (diseases, treatments), otological (behavioral), etc. starvation(total, protein, mineral, vitamin) cooling or overheating ionizing radiation.

Internal environmental factors

Thus, the susceptibility of the animal’s body and the influence of unfavorable external and internal environment serve as a prerequisite for the occurrence of an infectious disease, but the presence of a pathogen and a susceptible animal does not always lead to the development of an infectious disease.

TYPES OF INFECTIONS.

There are many types of infections. They are classified depending on the type of pathogen, the route of its penetration into the body, the location of the source of infection, etc.

Classification of infections.

Routes of entry of the pathogen:

Exogenous

Endogenous (autoinfection)

Cryptogenic

Method of infection:

Natural (spontaneous)

Artificial (experimental)

Pathogen spread:

Local (focal) in the body

Regional

Generalized

Number of pathogens

Simple (monoinfection)

Mixed

types of generalized infection:

Bacteremia (viremia) - a microorganism penetrates the blood and is carried by it, but does not multiply (tuberculosis, brucellosis, equine infectious anemia, swine fever);

Septicemia (sepsis) - microorganisms multiply in the blood and then spread to the organs and tissues of the body;

Pyemia is characterized by the formation of secondary purulent foci spreading along the lymphatic tract;

Septicopyemia is a combination of septicemia and pyaemia

Characteristics of infections.

Simple infection may be caused by a single pathogen; mixed- two or more pathogens (tuberculosis + brucellosis, rhinotracheitis + parainfluenza-3, salmonellosis + chlamydia).

Overt infection manifests itself external signs;hidden does not appear externally; at subinfections The pathogen enters the animal’s body in a dose less than infectious, and then quickly dies or is eliminated from the body. Reinfection - this is a re-infection after complete recovery with the same type of pathogen; occurs in the absence of immunity (for example: swine dysentery, foot rot, necrobacteriosis, tuberculosis). Secondary infection develops against the background of the first - main one (for example, pasteurellosis and salmonellosis against the background of swine fever; streptococcosis against the background of canine distemper or equine flu); superinfection - This is a re-infection of the body with the same pathogen (infection against the background of an existing one) until recovery and release from the pathogen that entered during the initial infection.

The cyclical course of the disease.

Infectious diseases are characterized by a certain cyclical course, or periodicity (stages), manifested by a sequential change of periods following one another. 1st period - incubation, or hidden (IP) - continues from the moment of penetration of the pathogen into organs and tissues until the appearance of the first, not yet clear clinical signs(and in case of latent infections - until positive results of diagnostic studies appear). This is an important epidemiological indicator. IP is characteristic of all infectious diseases, but its duration varies greatly: from several hours to days ( anthrax, foot and mouth disease, botulism, influenza, plague) up to several months and years (tuberculosis, brucellosis, leukemia, slow and prion infections). IP can be different even for the same disease. For most infectious diseases, the latent period is 1...2 weeks. Most often, animals in IP are not an active source of the infectious agent, but in some cases (rabies, foot-and-mouth disease, paratuberculosis), the pathogen can be released into the external environment already during the specified period.

2nd period - harbingers - or prodromal period, is not observed in all infectious diseases and usually lasts 1-2-3 days. It is characterized by initial painful manifestations that do not have any characteristic clinical features characteristic of a specific infectious disease. The complaints of patients during this period are general malaise, slight headache, pain and body aches, chills and moderate fever. The period of the main manifestations of the disease, the so-called “stationary” period, in turn can be divided into the stage of increasing painful phenomena, the period of the height of the disease and its decline. During the growth and height of the disease, the main clinical manifestations appear in a certain sequence (stages), characterizing it as an independent clinically defined disease.

Stationary period. During this period, along with the previously described biochemical and other changes accompanying endogenous intoxication, a whole cascade of changes occurs caused by toxic substances of the endogenous, previously harmless, own microflora of the body (autoflora) and the accumulation of substances resulting from the enzymatic, most often proteolytic breakdown of cells and body tissues (for example, with toxic hepatodystrophy). As a result of the combination of toxic substances of the exogenous microbe that caused the disease, and endogenous microflora with proteins of its own tissues (microbe + tissue, toxic agent + tissue), autoantigens are formed - carriers of foreign information, to which the body responds by producing autoantibodies to its own tissues (“its own, not its own”). having known"), acquiring pathogenic significance.

The period of the height of the disease - during the height of the disease, symptoms typical of this infectious disease appear, changes in the peripheral blood, as well as general manifestations(enlargement of the liver and spleen, changes in pulse rate in the form of tachycardia or relative bradycardia, arterial hypertension, and then hypotension, up to collapse, changes in the ECG), local manifestations are observed: rash on the skin (exanthema) and mucous membranes of the mouth (enanthema), dry mucous membranes, coated tongue, constipation or loose stools, enlarged lymph nodes, etc. are noted. With various infectious diseases, the periods of increase and height of the disease have unequal duration: from several hours (foodborne diseases) and several days (shigellosis, salmonellosis, cholera, plague etc.) up to one week (typhoid fever, hepatitis A) or several weeks, rarely up to a month or more (brucellosis, viral hepatitis B and C, yersiniosis, etc.). In most cases they end in recovery. These days, deaths are rare, but still occur (tetanus, botulism, meningococcal infection).

Definition of the concept “Infection-infectious process”

Infection, infectious process (Late Lat. infectio - infection, from Lat. inficio - introducing something harmful, infecting), the state of infection of the body; evolutionary complex biological reactions, arising from the interaction of the animal’s body and the infectious agent. The dynamics of this interaction is called the infectious process. There are several forms of infections. A pronounced form of infection is an infectious disease with a specific clinical picture (overt infection). With absence clinical manifestations infection is called latent (asymptomatic, latent, inapparent). Consequence hidden infection there may be the development of immunity, which is characteristic of the so-called immunizing subinfection. A unique form of infection is microbial carriage unrelated to previous illness.

If the route of penetration of microbes into the body is not established, the infection is called cryptogenic. Often, pathogenic microbes initially multiply only at the site of introduction, causing inflammatory process(primary affect). If inflammatory and dystrophic

changes develop in a limited area, at the location of the pathogen, called focal (focal), and when microbes are retained in the lymph nodes that control a certain area, they are called regional. When microbes spread in the body, a generalized infection develops. A condition in which microbes from the primary focus penetrate the bloodstream, but do not multiply in the blood, but are only transported to various organs, is called bacteremia. In a number of diseases (anthrax, pasteurellosis, etc.), septicemia develops: microbes multiply in the blood and penetrate all organs and tissues, causing inflammatory and degenerative processes there. If the pathogen, spreading from the primary lesion through the lymphatic tract and hematogenously, causes the formation of secondary purulent foci (metastases) in various organs, they talk about pyaemia. The combination of septicemia and pyaemia is called septicopyemia. A condition in which pathogens multiply only at the site of penetration, and their exotoxins have a pathogenic effect, is called toxemia (characteristic of tetanus).

Infection can be spontaneous (natural) or experimental (artificial). Spontaneous occurs in natural conditions during the implementation of the transmission mechanism characteristic of a given pathogenic microbe, or during the activation of opportunistic microorganisms that lived in the animal’s body (endogenous infection, or autoinfection). If a specific pathogen enters the body from the environment, we speak of an exogenous infection. An infection caused by one type of pathogen is called simple (monoinfection), and an infection caused by an association of microbes that have entered the body is called associative. In such cases, synergism sometimes appears - an increase in the pathogenicity of one type of microbe under the influence of another. When two different diseases occur simultaneously (for example, tuberculosis and brucellosis), the infection is called mixed. A secondary (secondary) infection is also known, which develops against the background of a primary (main) infection as a result of the activation of conditionally pathogenic microbes. If, after the disease has been transferred and the animal’s body has been freed from its pathogen, a second illness occurs due to infection with the same pathogenic microbe, they speak of reinfection. The condition for its development is maintaining sensitivity to this pathogen. Superinfection is also noted - a consequence of a new (repeated) infection that occurs against the background of an already developing disease caused by the same pathogenic microbe. Relapse, reappearance its symptoms after clinical recovery has occurred is called a relapse. It occurs when the animal’s resistance weakens and the pathogens of the disease that remain in the body are activated. Relapses are characteristic of diseases in which insufficiently strong immunity is formed (for example, equine infectious anemia).

Complete animal feeding optimal conditions their maintenance and operation are factors preventing the occurrence of infections. Factors that weaken the body act in exactly the opposite way. With general and protein starvation, for example, the synthesis of immunoglobulins decreases and the activity of phagocytes decreases. Excess protein in the diet leads to acidosis and decreased blood bactericidal activity. If there is a shortage minerals Water metabolism and digestion processes are disrupted, and it becomes difficult to neutralize toxic substances. With hypovitaminosis, the barrier functions of the skin and mucous membranes are weakened, and the bactericidal capacity of the blood decreases. Cooling leads to a decrease in the activity of phagocytes, the development of leukopenia, weakening barrier functions mucous membranes of the upper respiratory tract. When the body overheats, a conditionally pathogenic pathogen is activated. intestinal microflora, the permeability of the intestinal wall for microbes increases. Under the influence of certain doses ionizing radiation all protective barrier functions of the body are weakened. This promotes both autoinfection and the penetration of microorganisms from the outside. Typological characteristics and condition are important for the development of infections nervous system, state endocrine system and RES, metabolic rate. Breeds of animals are known that are resistant to certain infectious agents, the possibility of selecting resistant lines has been proven, and there is data on the influence of type nervous activity on the manifestation of infectious diseases. A decrease in the body's reactivity with deep inhibition of the central nervous system has been proven. This explains the sluggish, often asymptomatic course of many diseases in animals during hibernation. Immunological reactivity depends on the age of the animals. In young animals, the permeability of the skin and mucous membranes is higher, and less pronounced inflammatory reactions and adsorption capacity of RES elements, as well as protective humoral factors. All this contributes to the development specific infections young animals caused by opportunistic microbes. However, young animals have developed cellular protective function. The immunological reactivity of farm animals usually increases in summer time years (if overheating is excluded).