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 is various manifestations: from asymptomatic carrier to an infectious disease (with recovery or death).
infectious disease is an extreme form of infection.
An infectious disease is characterized by:
1) Availability certain live pathogen ;
2) infectiousness , i.e. pathogens can be transmitted from a sick person to a healthy one, which leads to a wide spread of the disease;
3) the presence of a certain incubation period and characteristic succession periods during the course of the disease (incubation, prodromal, manifest (height of the disease), recovalescence (recovery));
4) development characteristic of this disease clinical symptoms ;
5) presence immune response (more or less prolonged immunity after the transfer of the disease, the development of 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) from the properties of the pathogen ;
2) from the state of the macroorganism ;
3) from 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 an invasion).
Microorganisms that can cause infectious diseases are called pathogenic , i.e. disease-causing (pathos - suffering, genos - birth).
There are also conditionally pathogenic microorganisms that cause diseases with a sharp decrease in local and general immunity.
The causative agents of infectious diseases have properties pathogenicity and virulence .
pathogenicity and virulence.
pathogenicity- this is the ability of microorganisms to penetrate into a macroorganism (infectivity), take root in the body, multiply and cause a complex of pathological changes (disorders) in organisms sensitive to them (pathogenicity - the ability to cause an infectious process). Pathogenicity is a 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 the strain, which manifests itself under certain conditions (with the 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 artificially change (raise or lower). Raise carried out by repeated passage through the body of susceptible animals. downgrade - as a result of the impact of adverse factors: a) heat; b) antimicrobial and disinfectant substances; c) growing on unfavorable nutrient media; d) the body's defenses - passage through the body of little susceptible or non-receptive animals. Microorganisms with weakened virulence used to get live vaccines.
Pathogenic microorganisms also specificity, organotropism and toxicity.
Specificity- ability to call certain infectious disease. Vibrio cholerae causes cholera, Mycobacterium tuberculosis - tuberculosis, etc.
Organotropism- the ability to infect certain organs or tissues (the causative agent of dysentery - the mucous membrane of the large intestine, the influenza virus - the mucous membrane of the upper respiratory tract, the rabies virus - nerve cells ammon's horn). There are microorganisms that can infect any tissue, any organ (staphylococci).
Toxicity- the ability to form toxic substances. Toxic and virulent properties are closely related.
virulence factors.
Traits that determine pathogenicity and virulence are called virulence factors. These include certain morphological(the 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 (causative agents of anthrax, plague, pneumococci);
3) superficial substances of the capsule or cell wall of various nature (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 non-specific protective factors;
4) aggression enzymes: proteases destroying antibodies; coagulase, coagulating blood plasma; fibrinolysin, dissolving fibrin clots; lecithinase, destroying the lecithin of membranes; collagenase destroying 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 aggressors.
Virulence factors provide:
1) adhesion - attachment or adherence 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) into cells - epithelial, leukocytes, lymphocytes (all viruses, some types of bacteria: shigella, escherichia); cells die at the same time, and the integrity of the epithelial cover may be violated;
4) invasion - the ability to penetrate through the mucous and connective tissue barriers into the underlying tissues (due to the production of hyaluronidase and neuraminidase enzymes);
5) aggression - the ability of pathogens to suppress the nonspecific and immune defenses of the host organism 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 stand out into the environment after cell death.
Properties of endo and exotoxins.
|
Exotoxins |
Endotoxins |
|
Lipopolysaccharides |
|
|
Thermolabile (inactivated at 58-60С) |
Thermostable (withstand 80 - 100С) |
|
Highly toxic |
Less toxic |
|
specific |
Non-specific ( general action) |
|
High antigenic activity (cause the formation of antibodies - antitoxins) |
Weak antigens |
|
Under the action of formalin, they pass into toxoids (loss poisonous properties, preservation of immunogenicity) |
Partially neutralized with formalin |
|
Formed mainly by gram "+" bacteria |
Formed mainly by gram "-" bacteria |
Exotoxins form causative agents of the so-called toxinemia infections, which include difteria, tetanus, gas gangrene, botulism, some forms of staphylococcal and streptococcal infections.
Some bacteria simultaneously form both exo- and endotoxins (E. coli, Vibrio cholerae).
Getting exotoxins.
1) growing a toxigenic (forming exotoxin) 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 (the filtrate of the broth culture of toxigenic bacteria) and kept in a thermostat at 39-40C for 3-4 weeks; there is a loss of toxicity, but antigenic and immunogenic properties are preserved;
2) add preservative and adjuvant.
Anatoxins are molecular vaccines. They are used for specific prophylaxis of toxinemic infections , as well as to obtain therapeutic and prophylactic antitoxic sera, also used in toxin infections.
Getting endotoxins.
Various methods are used microbial cell destruction , and then cleaning is carried out, i.e. separation of endotoxin from other components of the cell.
Since endotoxins are lipopolysaccharides, they can be extracted from the microbial cell by breaking it down with TCA (trichloroacetic acid) followed by dialysis to remove proteins.
Definitions of the concepts "infection", "infectious process", "infectious disease" The term "Infection" (lat. Infectio - infection) - a set biological processes occurring in a macroorganism when pathogenic microorganisms are introduced into it, regardless of whether this introduction will entail the development of an overt or latent pathological process, or whether it will be limited only to temporary carriage or long-term persistence of the pathogen.
The infectious process is a complex of adaptive reactions of a macroorganism that develops in response to the introduction and reproduction of a pathogenic microorganism in it and is aimed at restoring homeostasis and disturbed biological balance with the environment. The infectious process occurs when there are three components: - pathogen, - susceptible macroorganism (patient), - factor of infection transmission from an infected organism to a healthy one. Infectious disease - An infectious disease is a violation of the normal functioning of the body, due to the introduction and reproduction of pathogenic microorganisms in it. Infectious disease can be defined as special case infectious process.
The place of penetration of the pathogen is called the entrance gate of infection - tissues deprived of physiological protection against a particular type of microorganisms serve as a place for its penetration into the macroorganism. Cylindrical epithelium for gonococci. Staphylococci, streptococci can penetrate in several ways Ways of penetration of the pathogen into the macroorganism: - through the mucous membrane (overcoming natural defense factors, microorganisms attach to epithelial cells and colonize it; then penetrate into lymphatic system, blood, tissues of internal organs, microorganisms attach to epithelial cells and colonize it) - through microtraumas of the skin (the pathogen, bypassing the natural barriers of the skin and mucous membranes, penetrates into the lymphatic system and into the blood)
Properties of pathogens: Pathogenicity (pathogenicity) is a specific multifactorial trait that characterizes the potential ability of a microbe to cause an infectious process. Invasiveness - the ability of the pathogen to penetrate through the skin and mucous membranes into the internal environment of the macroorganism, with subsequent possible spread through organs and tissues Toxigenicity - this is the ability of microbes to produce toxins
To determine the degree of pathogenicity, the concept is used as - virulence, which is an individual sign of any pathogenic strain. Degrees of virulence of the microorganism Depending on the degree of manifestation of this trait, all strains can be divided into high-, moderate-, low-virulence. The higher the virulence of the strain, the lower should be the infectious dose, which is the number of viable microbes that can cause the development of an infectious process in the host organism. The infectious dose of the pathogen is the minimum number of microbial cells that can cause an infectious process. The value of the infectious dose depends on the virulent properties of the pathogen. The higher the virulence, the lower the infectious dose. For the highly virulent pathogen Yersinia pestis (plague), a few bacterial cells of Shigella dysenteriae are enough - dozens of cells
Properties of the macroorganism 1. Susceptibility to a particular pathogen. 2. Resistance - a state of resistance, which is determined by factors of non-specific protection. Susceptibility - the ability of a macroorganism to respond to infection by the development of an infectious process. Susceptibility can be specific and individual. Species susceptibility is inherent in a given species of animal or person. It is genetically determined. A certain type of microbe finds the optimal environment for its existence in the tissues of a certain type of host.
Individual susceptibility is determined by the state of each specific organism. It depends on many factors: 1) the quality and quantity of the pathogen; quality - the severity of invasive and aggressive properties pathogen, quantity - infectious dose - a certain critical dose, below which the disease may not develop (for cholera, it is necessary to administer V. cholerae in a dose by oral route); 2) entry gate - a tissue or organ through which the pathogen enters the macroorganism; for most pathogens, penetration through certain entrance gates is necessary for the development of the disease (for gonococcus - only through the mucous membranes of the genital organs or the conjunctiva of the eye, for the causative agent of dysentery - through the mucous membrane of the colon, for the influenza virus - through the mucous membrane of the respiratory tract); there are microorganisms that can penetrate through any entrance gate (the causative agent of the plague, staphylococci).
3) general physiological reactivity of the organism; it is determined by the physiological characteristics of the macroorganism, the nature of metabolism, the function of internal organs, endocrine glands, features of immunity. The general physiological reactivity is affected by: a) gender and age: there are childhood infections (scarlet fever, whooping cough, measles, mumps), pneumonia is severe in old age, during pregnancy women are more susceptible to staphylococcal and streptococcal infections, up to 6 months children are resistant to many infections, tk. receive antibodies from the mother; b) the state of the nervous system: depression of the nervous system contributes to a more severe course of infection; mental disorders reduce the regulatory function of the central nervous system; c) presence somatic diseases(diabetes, diseases cardiovascular system, liver, kidneys);
D) state normal microflora, whose representatives have antagonistic properties; e) nutrition: with insufficient and malnutrition, people are more susceptible to infectious diseases (tuberculosis, dysentery, cholera), while highest value have protein components of food, vitamins and microelements (necessary for the synthesis of antibodies and the maintenance of active phagocytosis), as a result of starvation, not only individual, but also species immunity can be lost; lack of vitamins leads to metabolic disorders, which reduces resistance to infections; f) immunobiological features of the organism, i.e. stability of natural protective factors.
Influence of environmental factors on the course of the infectious process. Environmental factors affect both the microorganism, its resistance and persistence in the external environment, and the resistance of the macroorganism. Refrigeration reduces resistance to many pathogenic and opportunistic microbes. For example, exposure to cold and humid air reduces the resistance of the respiratory mucosa, leading to acute respiratory diseases during the autumn-winter period. Overheating reduces immunity. Air pollution leads to an increase in upper respiratory diseases in big cities. Solar radiation greatly increases resistance, but in some cases, prolonged and intense radiation reduces resistance (malaria relapses in people exposed to intense solar radiation). ionizing radiation in large doses, it makes the body defenseless against infection, disrupting the permeability of the mucous membranes, sharply reducing the functions lymphoid tissue and protective properties of blood. social conditions: normal conditions work, life, recreation, sports increase the body's resistance; poor sanitary and hygienic conditions, physical and mental fatigue cause a weakening of the body's defenses.
Forms of the infectious process. BY NATURE OF THE PATHOGENS: bacterial, viral, fungal, protozoal. BY ORIGIN: - exogenous - infection from the environment with food, water, soil, air, secretions of a sick person; - endogenous - infection with opportunistic microorganisms that live in the body of the person himself, which occurs with a decrease in immunity; - autoinfection - self-infection by transfer (usually by the hands of the patient) from one place to another (from the mouth or nose to the wound surface).
BY THE NUMBER OF PATHOGENS: - monoinfection - one species; - mixed - two or more types of pathogens. BY DURATION: - acute - short-term (from one week to a month); - chronic - protracted course (several months - several years); long stay - persistence.
BY LOCALIZATION: - focal - localized in the local focus; - generalized - the pathogen spreads through the body with blood (hematogenous route) or with lymph (lymphogenic route). Focal can go into generalized. Secondary infection - infection with another type of pathogen during the main disease (complication of the main disease by another microbe) - measles is complicated by pneumonia. Relapse - the return of symptoms due to pathogens remaining in the body ( relapsing fever, malaria). Reinfection - re-infection with the same species after recovery. Superinfection - infection with the same species during the disease (before recovery).
Features of infectious diseases Contagiousness (infectiousness) - the ability of the pathogen infectious disease be transmitted from an infected organism to a healthy one. Specificity - each pathogenic microorganism causes a disease characterized by a certain localization of the process and the nature of the lesion. Cyclicity - a change in periods of the disease, strictly following each other: incubation period - prodromal period - the height of the disease - convalescence
Meaning specific immunity Formation of specific immunity - in the process of developing an infectious process, specific immunity is formed, the intensity and duration of which can vary from several months to several years and even decades
2. Prodromal (prodrome) is a manifestation of common symptoms - discomfort, fatigue, chills. Clinically, it is intoxication. Localization of the pathogen - penetrates into the blood, lymph, secretion of toxins occurs, the activity of innate immunity factors is manifested
Classification of infectious diseases Intestinal infections Respiratory tract infections Blood infections Zoonotic infections Contact - household infections The causative agent is excreted in feces or urine. Transmission factors: food, water, flies, dirty hands, household items. Infection through the mouth. Transmission by airborne droplets or airborne dust The pathogen is transmitted through insect bites Diseases transmitted through animal bites Transmitted by contact with a sick person
Group of infectious diseases Infections included in the group Intestinal infections Typhoid fever, paratyphoid A and B, dysentery, cholera, food poisoning etc. Respiratory tract infections, or airborne infections Influenza, measles, diphtheria, scarlet fever, smallpox, tonsillitis, tuberculosis Blood infections Sypsis and relapsing fever, malaria, plague, tularemia, tick-borne encephalitis, AIDS Zoonotic infections Rabies Contact-household Infectious skin and venereal diseases, sexually transmitted (syphilis, gonorrhea, chlamydia, etc.)
Ways of spread of infections Fecal-oral This way all intestinal infections are transmitted. The microbe with feces, vomit of the patient gets on food products, water, dishes, and then through the mouth into gastrointestinal tract healthy person Fecal-oral This way all intestinal infections are transmitted. The microbe with feces, vomit of the patient gets on food, water, dishes, and then through the mouth into the gastrointestinal tract of a healthy person. Liquid Characteristic for blood infections. Carriers of this group of diseases are blood-sucking insects: fleas, lice, ticks, mosquitoes, etc. Liquid Characteristic for blood infections. Carriers of this group of diseases are blood-sucking insects: fleas, lice, ticks, mosquitoes, etc. Contact or household contact This way most venereal diseases are transmitted through close contact between a healthy person and a sick person Contact or household contact This way most venereal diseases are transmitted through close contact between a healthy person and a sick person Infection occurs through bites or close contact with sick animals. Zoonotic Carriers of zoonotic infections are wild and domestic animals. Infection occurs through bites or close contact with sick animals. Airborne viral diseases upper respiratory tract. The virus with mucus, when sneezing or talking, enters the mucous membranes of the upper respiratory tract of a healthy person. Airborne This way all viral diseases of the upper respiratory tract spread. The virus with mucus, when sneezing or talking, enters the mucous membranes of the upper respiratory tract of a healthy person. The main ways of transmission of infection and their characteristics
Epidemiology is a science that studies the conditions for the occurrence and mechanisms of spread epidemic process. The epidemiological process is a chain of continuous, one after another infectious conditions (from asymptomatic carriage to a manifest disease) as a result of the circulation of the pathogen in the team.
The epidemic process is the emergence and spread among the population of specific infectious conditions, from asymptomatic carriers to manifest diseases caused by the circulation of the pathogen in the team. Manifest form of the disease - clinical form diseases with a full range of characteristic symptoms. The asymptomatic form is hidden.
1. Source of infection - a living or abiotic object, which is a place of natural activity of pathogenic microbes, due to which people and animals are infected. The source of infection can be a human and animal organism, abiotic objects of the environment (water, food).
Source of the causative agent of the infection external environment or directly transmitted to another susceptible organism An organism that does not show signs of disease. They represent a great danger to others, since it is much more difficult to identify them than patients. An organism that does not show signs of disease. They represent a great danger to others, since it is much more difficult to identify them than patients.
2. Mechanism of transmission - a way of moving infectious agents and invasive diseases from an infected organism to a susceptible one. Includes 3 phases: a) removal of the pathogen from the host organism into the environment; b) the presence of the pathogen in environmental objects (biotic and abiotic); c) the introduction of the pathogen into a susceptible organism. Transmission mechanisms are distinguished: fecal-oral, aerogenic, transmissible, contact
Transmission factors are elements of the environment that ensure the transfer of microbes from one organism to another. Ways of transmission - an element of the external environment, ensuring the entry of the pathogen from one organism to another, under certain external conditions. For the fecal-oral mechanism, there are ways: alimentary (food), water and contact-household. For the aerogenic mechanism, there are ways: air-droplet and air-dust.
3. Susceptible collective, if the immune layer in the population is 95% or more, then in this collective the state of epidemic well-being is achieved. Therefore, the task of preventing epidemics is to create an immune layer in the collectives through vaccination.
Prevention of infectious diseases is a set of measures aimed at ensuring a high level of people's health, their creative longevity, eliminating the causes of diseases, improving working conditions, living and recreation of the population, and protecting the environment.
Anti-epidemic (anti-epizootic) and sanitary and hygienic measures for the early detection of patients and those suspicious of the disease by going round the yards; enhanced medical and veterinary surveillance of those infected, their isolation and treatment; sanitization people disinfection of clothes, shoes, care items, etc.; disinfection of the territory, structures, transport, residential and public premises; establishment of an anti-epidemic mode of operation of medical and preventive and other medical institutions; disinfection of food waste, sewage and waste products of sick and healthy individuals; carrying out sanitary and educational work
3 degrees of intensity of the epidemic process: I - Sporadic morbidity - the level of morbidity of a given nosological form in a given territory in a certain historical period of time; II - Epidemic - the level of incidence of a given nosological form in a certain area in a specific period of time, sharply exceeding the level of sporadic incidence; III - Pandemic level, sharply exceeding the epidemic. The pandemic is spreading very quickly, capturing a country, a continent, the whole world. An epidemic smaller than a pandemic covers a city, region, country.
Quarantine (conventional) diseases are the most dangerous diseases prone to rapid spread. Hospital (nosocomial) infections - diseases that occur in weakened individuals who become infected in hospital conditions (suppuration postoperative wounds, pneumonia, sepsis). The fight against epidemics is aimed at all 3 links of the epidemic process. But with each disease, the emphasis is on the most important link (for intestinal infections - interruption of transmission routes; for airborne infections - the creation of collective immunity).
Particularly dangerous (HSV), as they cause severe complications v human body and may even cause death. Such infections should be kept under public health control, providing a number of measures that would prevent the spread of these diseases. A set of such measures is called quarantine, and infections that are subject to special medical and sanitary attention are called quarantine. The list of quarantine diseases has changed over time. Some of them could be overcome by vaccination, others remained dangerous. Currently, it is customary to call quarantine only a group of special dangerous infections(OOI): - yellow fever - plague - smallpox - cholera
31. The concept of infection. Conditions for the occurrence of an infectious process.
Infection (Latin infectio - I infect) is a state of infection caused by the interaction of an animal organism and a pathogenic microbe. The reproduction of pathogenic microbes that have invaded the body causes a complex of protective and adaptive reactions, which are a response to the specific pathogenic action of the microbe. Reactions are expressed in biochemical, morphological and functional changes, in the immunological response and are aimed at maintaining constancy internal environment body (homeostasis).
The state of infection, like any biological process, is dynamically revealed through the infectious process. On the one hand, the infectious process includes the introduction, reproduction and spread of the pathogen in the body, its pathogenic action, and on the other hand, the reaction of the body to this action. The body's responses, in turn, divide the condition into two groups: infectious-pathological and protective-immunological. Therefore, the infectious process is the pathogenetic essence of an infectious disease.
The pathogenic (harmful) effect of the infectious agent in quantitative and qualitative terms may be different. Under specific conditions, it manifests itself in some cases in the form of an infectious disease of varying severity, in others - without pronounced symptoms. clinical symptoms, in the third - only changes detected by microbiological, biochemical and immunological methods of research. It depends on the quantity and quality of a specific pathogen, the possibility of its penetration into the body of a susceptible animal, the conditions of the internal and external environment that determine the nature of the interaction of micro- and macroorganism.
The state of infection, like any biological process, is dynamic. the dynamics of the reaction of interaction between micro- and macroorganism is called an infectious process. The infectious process, on the one hand, includes the introduction, reproduction and spread of a pathogenic microbe in the body, and on the other hand, the body's reaction to this action. These reactions are expressed in biochemical, morphological, functional and immunological changes aimed at maintaining the constancy of the internal environment of the body.
For the occurrence of an infectious disease, a number of conditions are necessary:
the microorganism must be sufficiently virulent;
The host organism must be susceptible to this pathogen;
It is necessary to introduce a certain number of microorganisms;
microorganisms must enter the body through the most favorable gates of infection and reach susceptible tissues;
· environmental conditions should be conducive to the interaction between micro- and macroorganism.
The fate of pathogenic microbes that enter the body can be different depending on the state of the body and the virulence of the pathogen. Some microbes, having got into certain organs with the blood flow, linger in their tissues, multiply, causing disease. Any infectious disease, regardless of the clinical signs and location of the pathogen, is a disease of the whole organism.
If the disease is caused by one pathogen, then it is called a monoinfection. When the cause of the disease is two or more pathogens, then they speak of a mixed infection. For example, large cattle can suffer from tuberculosis and brucellosis at the same time.
A secondary or secondary infection is an infection that occurs after a primary (primary) infection. For example, with swine fever, a secondary infection is pasteurellosis. The causative agents of secondary infections are opportunistic microflora, which is a permanent inhabitant of the animal body and shows its virulent properties when the body's defenses are weakened.
Most infectious diseases are characterized by the presence of certain, pronounced clinical signs. This form of the disease is called typical. The infectious process can quickly end with the recovery of the animal - this is a benign course. With a reduced natural resistance of the organism and the presence of a highly virulent pathogen, the disease can take a malignant course, characterized by high mortality.
Depending on the nature of the manifestation and the affected organ system, infectious diseases are divided into intestinal (colibacteriosis, salmonellosis), respiratory (tuberculosis), infections of the skin and mucous membranes (tetanus, foot and mouth disease). pathogens intestinal infections are transmitted by alimentary means (food, water). Respiratory tract infections are spreading by airborne droplets, less often air-dust. The causative agents of infections of the skin and mucous membranes are transmitted through household items, through direct contact (rabies bites) or sexually (campylobacteriosis).
According to the nature of the occurrence, exogenous and endogenous infections are distinguished. In the case when infection occurs as a result of the entry of microorganisms from outside, they speak of an exogenous (heterogeneous) infection (foot and mouth disease, anthrax, plague). In the case where the conditional pathogenic microorganisms show their pathogenic properties when a number of circumstances associated with a reduced resistance of the macroorganism coincide, they speak of endogenous (spontaneous, autoinfection) infection.
Infectious diseases It is customary to divide into anthroponotic, zoonotic and zooanthroponotic. diseases (cholera, typhoid fever etc.), which only a person suffers from, are called anthroponotic (anthroponoses). Diseases that affect only animals are called zoonotic (zoonoses), such as glanders, myt, bordetellosis. Diseases that affect humans and animals are called zooanthroponoses (brucellosis, yersiniosis, leptospirosis) or zooanthroponoses.
Infection- this is a state of infection that occurs as a result of the penetration of m-s into the macroorganism.
infectious process is the dynamics of interaction between micro- and macroorganism.
If the pathogen and the animal organism (host) meet, then 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 former is much broader).
Forms of infection:
- Overt infection or infectious disease - the most striking, clinically expressed form of infection. The pathological process is characterized by certain clinical and pathological features.
- Latent infection (asymptomatic, latent) - the infectious process is not externally (clinically) manifested. 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 recover in bacterial form with its properties.
- Immunizing subinfection – the pathogen that enters the body causes specific immune reactions, dies or is excreted; the body does not become a source of the infectious agent, and functional disorders do not appear.
- Microcarrying – the infectious agent is present in the body of a clinically healthy animal. Macro- and microorganism are in a state of equilibrium.
Latent infection and microbe carrying are not the same thing. At latent infection it is possible to determine the periods (dynamics) of the infectious process (occurrence, course and extinction), as well as the development of immunological reactions. This cannot be done with microbes.
For the occurrence of an infectious disease, a combination of the following factors is necessary:
- the presence of a microbial agent;
- susceptibility of the macroorganism;
- the presence of an environment in which this interaction takes place.
Forms of the course of an infectious disease:
- Superacute (lightning) flow. In this case, the animal dies due to rapidly developing septicemia or toxinemia. Duration: few hours. Typical Clinical signs with this form they do not have time to develop.
- Acute course . Duration: from one to several days. Typical clinical signs in this form appear violently.
- Subacute flow.Duration: longer than acute. Typical clinical signs in this form are less pronounced. Pathological changes are characteristic.
- Chronic course.Duration: can drag on for months and even years. Typical clinical signs are mild or absent. The disease takes such a course when the pathogen does not have a high virulence or the body is sufficiently resistant to infection.
- Abortive course. With an abortive course, the development of the disease suddenly stops (breaks off) and recovery occurs. Duration: abortive disease is short-lived. Manifested in mild form. Typical clinical signs are mild or absent. The reason for this course of the disease is considered to be the increased resistance of the animal.
Infection(lat. Infectio I infect) is a state of infection caused by the interaction of an animal organism and a pathogenic microbe. Reproduction of pathogenic microbes that have invaded the body causes a complex of pathological and protective-adaptive reactions, which are a response to the specific pathogenic action of the microbe. Reactions are expressed in biochemical, morphological and functional changes, in the immunological response and are aimed at maintaining the constancy of the internal environment of the body (homeostasis).
The state of infection, like any biological process, is dynamic. The dynamics of interaction reactions between micro- and macroorganisms is called infectious process. On the one hand, the infectious process includes the introduction, reproduction and spread of the pathogen in the body, its pathogenic action, and on the other hand, the reaction of the body to this action. The body's responses, in turn, are conditionally divided into two groups (phases): infectious-pathological and protective-immunological.
Therefore, the infectious process is the pathogenetic essence of an infectious disease.
The pathogenic (harmful) effect of the infectious agent in quantitative and qualitative terms may be different. Under specific conditions, it manifests itself in some cases in the form of an infectious disease of varying severity, in others - without pronounced clinical signs, in others - only changes detected by microbiological, biochemical and immunological methods of research. It depends on the quantity and quality of the specific pathogen that has penetrated into the susceptible organism, the conditions of the internal and external environment that determine the resistance of the animal and the nature of the interaction of the micro- and macroorganism.
According to the nature of the interaction between the pathogen and the animal organism, three forms of infection are distinguished.
The first and most striking form of infection is infectious disease. It is characterized outward signs disturbances in the normal functioning of the body, functional disorders and morphological tissue damage. An infectious disease that manifests itself with certain clinical signs is referred to as an overt infection. Often, an infectious disease is not clinically manifested or is hardly noticeable, and the infection remains latent (asymptomatic, latent, inapparent). However, in such cases, with the help of bacteriological and immunological studies, it is possible to identify the presence of an infectious process characteristic of this form of infection - the disease.
The second form of infection includes microcarriers that are not associated with a previous illness of the animal. In such cases, the presence of the infectious agent in the organs and tissues of a clinically healthy animal does not lead to pathological condition and is not accompanied by an immunological restructuring of the body. With microbearing, the existing balance between the micro- and macroorganism is maintained natural factors resistance. This form of infection is established only by microbiological research. Microcarriage is quite often recorded in many diseases among healthy animals of both susceptible and non-susceptible species (causative agents of swine erysipelas, pasteurellosis, clostridiosis, mycoplasmosis, malignant catarrhal fever, etc.). In nature, there are other types of microcarriage (for example, by convalescents and recovered animals), and they must be differentiated from an independent form of infection - microcarriage by healthy animals.
The third form of infection includes an immunizing subinfection, in which the microbes that enter the animal's body cause only a specific restructuring and immunity, but the pathogens themselves die. The body does not experience functional disorders and it does not become a source of infection. Immunizing subinfection, as well as microcarriage, is widespread in nature, but has not yet been studied enough (for example, with leptospirosis, emkar, etc.), so it is difficult to control it when implementing antiepizootic measures.
Differentiated Approach to the forms of infection makes it possible to correctly diagnose infectious diseases and to identify infected animals in a dysfunctional herd as much as possible.
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Infection(Latin infectio - infection) is a set of biological processes that arise and develop in the body when pathogenic microbes are introduced into it.
The infectious process consists of the introduction, reproduction and spread of the pathogen in the body, its pathogenic action, as well as the reaction of the macroorganism to this action.
There are three forms of infection:
1. An infectious disease characterized by a disruption in the normal functioning of the animal organism, organic, functional disorders and morphological damage to tissues. An infectious disease may not manifest clinically or be subtle; then the infection is called latent, latent. An infectious disease in this case can be diagnosed using various additional research methods.
2. Microcarriage, not associated with the illness of the animal. A balance is maintained between the micro- and macroorganism due to the resistance of the macroorganism.
3. An immunizing infection is such a relationship between a micro- and macroorganism that causes only a specific restructuring in immunity. functional disorders does not occur, the animal organism is not a source of the infectious agent. This form is widespread but not well understood.
Commensalism- a form of cohabitation, when one of the organisms lives at the expense of the other, without causing him any harm. Commensal microbes are representatives of the normal microflora of an animal. With a decrease in the body's resistance, they can also show a pathogenic effect.
Mutualism- a form of symbiosis, when both organisms derive mutual benefit from their cohabitation. A number of representatives of the normal microflora of animals are mutualists that benefit the owner.
The pathogenicity factors of microorganisms are divided into two groups, which determine:
invasiveness of microorganisms- the ability of microorganisms to penetrate through immunological barriers, skin, mucous membranes into tissues and organs, multiply in them and resist the immune forces of the macroorganism. Invasiveness is due to the presence in the microorganism of a capsule, mucus, surrounding the cell and opposing phagocytosis, flagella, pili, responsible for attaching microorganisms to the cell, and the production of enzymes hyaluronidase, fibrinolysin, collagenase, etc.;
toxigenicity- the ability of pathogenic microorganisms to produce exo- and endotoxins.
Exotoxins- products of microbial synthesis released by the cell into the environment. These are proteins with high and strictly specific toxicity. It is the action of exotoxins that determines the clinical signs of an infectious disease.
Endotoxins are part of the bacterial cell wall. They are released when the bacterial cell is destroyed. Regardless of the microbe-producer, endotoxins cause the same type of picture of the pathological process: weakness, shortness of breath, diarrhea, hyperthermia develop.
The pathogenic effect of viruses is associated with their reproduction in the cell of a living organism, leading to its death or to the elimination of its functional activity, but an abortive process is also possible - the death of the virus and the survival of the cell. Interaction with the virus can lead to cell transformation and tumor formation.
Each infectious agent has its own spectrum of pathogenicity, i.e. the range of susceptible animals where microorganisms realize their pathogenic properties.
There are obligately pathogenic microbes. The ability to cause an infectious process is their constant species feature. There are also facultative pathogenic (conditionally pathogenic) microorganisms, which, being commensals, cause infectious processes only when the resistance of their host is weakened. The degree of pathogenicity of microorganisms is called virulence. This is an individual feature of a specific, genetically homogeneous microbe strain. Virulence may vary depending on the conditions of existence of microorganisms.
In the case of acute infectious diseases, when pathogens enter the body of a hardy animal, as a rule, the animal becomes ill.
Such pathogens fully satisfy the three conditions of the postulate of Henle and Koch:
1. The microbe-causative agent should be detected in this disease and not occur either in healthy people or in patients with other diseases.
2. The microbe-causative agent must be isolated from the patient's body in pure form.
3. A pure culture of the isolated microbe must cause the same disease in a susceptible animal.
At present, this triad has largely lost its significance.
A certain group of pathogens does not satisfy the Koch triad: they are isolated from healthy animals and from patients with other infectious diseases. They are of low virulence, and experimental reproduction of the disease in animals fails. The causal role of these pathogens is difficult to establish.
Types of infection. Depending on the mode of infection, there are the following types infections:
exogenous - the causative agent of the infection enters the body from the environment;
endogenous, or autoinfection, - occurs when the protective properties of the body are weakened and the virulence of opportunistic microflora increases.
Depending on the spread of microorganisms in the body of animals, the following types of infection are distinguished:
local, or focal, infection - the causative agent of the disease multiplies at the site of introduction into the body;
generalized - the causative agent of the disease from the place of introduction spreads throughout the body;
toxic infection - the pathogen remains at the site of introduction into the body, and its exotoxins enter the bloodstream, causing a pathogenic effect on the body (tetanus, infectious enterotoxemia);
toxicosis - exotoxins of microorganisms enter the body with food, they play the main pathogenetic role;
bacteremia / viremia - pathogens from the site of introduction penetrate into the blood and are transported by blood and lymph to various bodies and tissues multiply there too;
septicemia / sepsis - reproduction of microorganisms occurs in the blood, and the infectious process is characterized by seeding of the whole organism;
pyemia - the pathogen spreads by the lymphogenous and hematogenous route during internal organs and multiplies in them not diffusely (bacteremia), but in separate foci, with accumulation of pus in them;
septicopyemia is a combination of sepsis and pyemia.
The pathogen can cause various forms infectious disease, depending on the ways of penetration and spread of microbes in the body of animals.
Dynamics of the infectious process. Infectious diseases differ from non-infectious ones in specificity, contagiousness, staging of the course and the formation of post-infectious immunity.
Specificity - an infectious disease is caused by a certain type of microorganism.
Contagiousness - the ability of an infectious disease to spread by transmitting the pathogen from a sick animal to a healthy one.
The staging of the course is characterized by incubation, prodromal (preclinical) and clinical periods, the outcome of the disease.
The period from the moment the microbe enters the body of the animal until the first symptoms of the disease appear is called the incubation period. It is not the same and ranges from one or two days (flu, anthrax, botulism) to several weeks (tuberculosis), several months and years (slow viral infections).
During the prodromal period, the first non-specific symptoms diseases - fever, anorexia, weakness, depression, etc. Its duration is from several hours to one or two days.
Historically, the word "infection ” (lat. inficio - infect) was first introduced to refer to sexually transmitted diseases.
Infection- the totality of all biological phenomena and processes that occur in the body during the introduction and reproduction of microorganisms in it, the result of the relationship between the macro- and microorganism in the form of adaptive and pathological processes in the body i.e. infectious process.
infectious disease- the most pronounced form of the infectious process.
The term infection or a synonym for infectious process means a set of physiological and pathological regenerative-adaptive reactions that occur in a susceptible macroorganism under certain environmental conditions as a result of its interaction with pathogenic or opportunistic bacteria, fungi and viruses that have penetrated and multiply in it and are aimed at maintaining the constancy of the internal macroorganism environment (homeostasis). A similar process, but caused by protozoa, helminths and insects - representatives of the kingdom Animalia, is called invasion.
The occurrence, course and outcome of the infectious process are determined by three groups of factors: 1) quantitative and qualitative characteristics of the microbe - the causative agent of the infectious process; 2) the state of the macroorganism, the degree of its susceptibility to the microbe; 3) the action of physical, chemical and biological factors of the environment surrounding the microbe and macroorganism, which determines the possibility of establishing contacts between representatives different types, the commonality of the habitat of different species, food ties, the density and number of populations, the features of the transfer of genetic information, the features of migration, etc. At the same time, in relation to a person, environmental conditions should primarily be understood social conditions his life activity. The first two biological factors are direct participants in the infectious process that develops in a macroorganism under the action of a microbe. At the same time, the microbe determines the specificity of the infectious process, and the decisive integral contribution to the form of manifestation of the infectious process, its duration, severity of manifestations and outcome is made by the state of the macroorganism, primarily the factors of its nonspecific resistance, which come to the aid of factors of specific acquired immunity. The third, environmental, factor has an indirect effect on the infectious process, reducing or increasing the susceptibility of the macroorganism, or reducing and increasing the infectious dose and virulence of the pathogen, activating the mechanisms of infection and the corresponding routes of infection transmission, etc.
Mutualism- mutually beneficial relationship (for example, normal microflora).
Commensalism- one partner (microbe) benefits without causing much harm to the other. It should be noted that in any type of relationship, a microorganism can manifest its pathogenic properties (for example, conditionally pathogenic microbes-commensals in an immunodeficient host).
pathogenicity(“disease-producing”) is the ability of a microorganism to cause a disease. This property characterizes species genetic features of microorganisms, their genetically determined characteristics, allowing to overcome defense mechanisms host, to show their pathogenic properties.
Virulence - phenotypic(individual) quantitative expression of pathogenicity (pathogenic genotype). Virulence may vary and can be determined laboratory methods(more often - DL50 - 50% lethal dose - the amount of pathogenic microorganisms that can cause the death of 50% of infected animals).
According to their ability to cause diseases, microorganisms can be divided into pathogenic, conditionally pathogenic, non-pathogenic. Conditionally pathogenic microorganisms are found in environment and in the normal microflora. Under certain conditions (immunodeficiency states, injuries and operations with the penetration of microorganisms into tissues), they can cause endogenous infections.
3) Factors of pathogenicity of microorganisms: adhesins. Factors of invasion and aggression. Tropism of microbes. Relationship between microbial cell structure and pathogenicity factors.
The main factors of pathogenicity of microorganisms- adhesins, pathogenicity enzymes, substances that inhibit phagocytosis, microbial toxins, under certain conditions - capsule, microbial motility. Virulence is associated with toxigenicity(ability to produce toxins) and invasiveness(the ability to penetrate into the tissues of the host, multiply and spread). Toxigenicity and invasiveness have independent genetic control and are often inversely related (a pathogen with high toxigenicity may have low invasiveness and vice versa).
Adhesins and colonization factors more often surface structures of a bacterial cell, with the help of which bacteria recognize receptors on cell membranes, attach to them and colonize tissues. The function of adhesion is performed pili, outer membrane proteins, LPS, teichoic acids, viral hemagglutinins. Adhesion is a trigger mechanism for the implementation of pathogenic properties of pathogens.
Factors of invasion, penetration into cells and tissues of the host. Microorganisms can multiply outside cells, on cell membranes, inside cells. Bacteria secrete substances that help to overcome the host's barriers, their penetration and reproduction. In Gram-negative bacteria, these are usually outer membrane proteins. These factors include pathogenicity enzymes.
Enzymes of pathogenicity are factors of aggression and protection of microorganisms. The ability to form exoenzymes largely determines the invasiveness of bacteria - the ability to penetrate mucous, connective tissue and other barriers. These include various lytic enzymes - hyaluronidase, collagenase, lecithinase, neuraminidase, coagulase, proteases. Their characteristics are given in more detail in the lecture on the physiology of microorganisms.
4) Bacterial toxins: exotoxins and endotoxins, nature and properties, mechanisms of action.
The most important factors pathogenicity is considered toxins which can be divided into two large groups - exotoxins and endotoxins.
Exotoxins are produced into the external environment (host organism), usually of a protein nature, can exhibit enzymatic activity, can be secreted by both gram-positive and gram-negative bacteria. They are highly toxic, thermally unstable, and often exhibit antimetabolite properties. Exotoxins show high immunogenicity and cause the formation of specific neutralizing antibodies - antitoxins. According to the mechanism of action and point of application, exotoxins differ - cytotoxins (enterotoxins and dermatonecrotoxins), membrane toxins (hemolysins, leukocidins), functional blockers (cholerogen), exfoliants and erythrogenins. Microbes capable of producing exotoxins are called toxigenic.
Endotoxins are released only when bacteria die, are characteristic of gram-negative bacteria, are complex chemical compounds cell wall (LPS) - see the lecture on chemical composition bacteria. Toxicity is determined by lipid A, the toxin is relatively heat resistant; immunogenic and toxic properties less pronounced than in exotoxins.
The presence of capsules in bacteria complicates the initial stages of protective reactions - recognition and absorption (phagocytosis). An essential factor of invasiveness is the mobility of bacteria, which determines the penetration of microbes into cells and into intercellular spaces.
Pathogenicity factors are controlled by:
chromosome genes;
Plasmid genes;
Genes introduced by temperate phages.
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