The causative agents of infectious diseases include. Biological factors (living pathogens, infection and infectious process)
Infectious diseases occupy a special place in the pathology of animals. They differ from non-communicable diseases in that they are caused by certain living pathogens (bacteria, viruses, pathogenic fungi, rickettsia, mycoplasmas, chlamydia) or their metabolic products, are transmitted from a sick animal to a susceptible healthy one, and some of them tend to spread widely, causing significant economic damage. Among them are diseases transmitted from animals to humans (zooanthroponosis).
According to the degree of intensity of the manifestation of the epizootological process, three forms are distinguished: sporidia - single cases of the disease, epizootic - has a tendency to widespread (encompasses an area, region), panzootia - the highest degree of manifestation, when the disease can cover several countries. Enzootia reflects the confinement of the epizootic process to a specific area.
Brief morphology of the main microorganisms that cause infectious diseases.
Bacteria - A large group of predominantly unicellular microbes. Spore-forming aerobic bacteria are called bacilli, and anaerobic bacteria are called clostridia. There are three main forms of bacteria: spherical (cocci), rod-shaped (bacteria, bacilli, clostridia) and spiral (virions, spirillas).
Viruses - strict intracellular parasites, they are divided into two groups: containing deoxyribonucleic acid (DNA) and containing ribonucleic acid (RNA). Viruses differ from other microorganisms in that they are very small, able to pass through bacterial filters. They do not grow on artificial nutrient media, but multiply only in the cells of susceptible microorganisms (chicken embryos and tissue cultures).
Mycoplasmas - the smallest of bacteria, they are motionless, do not form spores, grow on complex nutrient media, are polymorphic, since they have no true cell wall. Mark spherical, granular, filiform, ring-shaped. Mycoplasmas pass through bacterial filters and grow on media that do not contain living cells, so they occupy an intermediate position between bacteria and viruses.
Rickettsia - a group of microorganisms that occupies an intermediate position between bacteria and viruses. They are similar to bacteria in morphology and antigenic properties. They belong to obligate parasites, live and multiply only in living cells, which brings them closer to viruses, have a coccoid, rod-shaped or filiform shape, do not form spores and capsules, are motionless.
The place of penetration of the pathogenic pathogen (microbe) into the body of the animal is called the gateway of infection. They can be the skin, conjunctiva, mucous membranes of the respiratory tract and digestive tract, genitourinary system, and in the embryonic period, the placenta. Each type of pathogen has evolutionarily adapted to such gates of infection that provide it with the most favorable conditions for life, and many of them have adapted to different routes of introduction.
Knowledge of the pathways of pathogenic microbes into the animal’s body is necessary for the organization of effective infection prevention.
For infectious diseases, a characteristic feature is the staged nature of their course, manifested by a successive change in the incubation (latent), prodromal (preclinical) and clinical periods with a favorable (recovery and formation of immunity) or fatal outcome.
Incubation period
- the period of time from the moment the microbe is introduced into the susceptible organism until the first clinical signs appear. Its duration varies and varies from several hours or days, to several weeks, months, and even several years (with slow infections).
After the incubation period, a long one (precursor stage, preclinical) sets in, lasting from several hours to 1-2 days and characterized by nonspecific clinical signs: weakness, depression, decreased appetite, and sometimes a slight increase in body temperature.
Then comes the period of complete development of the disease, the manifestation of the main, typical clinical signs that are taken into account when making a diagnosis. The duration of this period is different and depends on many factors. With a favorable course of the infectious process, the period of extinction of the disease begins, which is replaced by a period of clinical recovery (convalescence) of the animal and the formation of immunity.
Immunity - the state of the body's immunity to the effects of pathogenic agents or products of their vital activity.
Types of immunity. By origin, they distinguish between innate (species, hereditary) and acquired immunity, which develops as a result of a reaction to the action of pathogenic microbes that have penetrated the body and caused an infectious process (naturally acquired) or as a result of artificial immunization (artificially acquired).
The introduction of blood sera or their globulins containing ready-made antibodies, causes artificial passive immunity. This type of immunity also includes colostral immunity, when antibodies are transmitted with colostrum from the mother to the calf.
The immunity that persists after the body is released from the causative agent of the disease is called sterile. If the ill animal acquires immunity, but is not exempted from the pathogen microbe, they speak of non-sterile immunity.
With an unfavorable outcome of an infectious disease, animals die. A prerequisite for the occurrence of an infectious disease is the presence of a source of the pathogen, the mechanism of transmission factors and susceptibility of the livestock.
The diagnosis of an infectious disease is made in a comprehensive manner, while taking into account epizootological data, clinical signs, pathological signs, pathological changes, and conduct laboratory tests. When confirming the diagnosis, quarantine-restrictive measures are carried out.
Quarantine - a system of anti-epizootic measures aimed at the complete separation of dysfunctional groups of animals and their breeding territories with prosperous farms and territories in order to eliminate the disease and prevent its spread. Quarantine is carried out in relation to the most dangerous diseases (including for humans) or those with a tendency to widespread distribution.
Under the terms of quarantine are prohibited:
1) the movement of animals without the permission of the head veterinarian of the economy;
2) the introduction of susceptible animals into a dysfunctional economy;
3) the export of products and raw materials of animal origin, feed, as well as their import;
4) travel through a dysfunctional point, access by strangers to the farm;
5) the holding of exhibitions, fairs, bazaars and other public events at this time terminate economic relations with other farms.
On the roads leading to a dysfunctional point, special signs are posted, barriers are installed, equip and indicate detour routes, round-the-clock quarantine posts are organized, disbarriers are equipped and vehicles are disinfected. In some highly dangerous diseases, the staff are completely sanitized using sanitary checkpoints and steam-formalin chambers for disinfecting clothes. Slaughter of the entire susceptible outbreak population is foreseen. Restrictive measures - a lesser degree of separation than quarantine. They are carried out in an epizootic focus, a dysfunctional point in infectious diseases that do not tend to be widespread.
In many especially dangerous diseases, after quarantine is removed on the farm, certain term restrictions remain on the use of livestock products, feed, manure, pastures, water sources, etc.
The term for quarantine removal and restrictions depends on the length of the incubation period.
Treatment
animals with infectious diseases are considered as an event that reduces economic damage. It should be cost effective. Allocate a specific treatment, which consists in the normalization of the physiological functions of the body. Apply gamma globulins, in rare cases, vaccines, bacteriophages of antagonist microbes, antibiotics, chemotherapeutic agents.
Symptomatic therapy consists in the use of a variety of dietary and therapeutic agents that normalize the various functions of the body. For this, cardiovascular, antipyretic, astringent, laxatives and other drugs are used.
Infectious Disease Prevention
- a system of measures to ensure the prevention of the occurrence and spread of diseases in successful farms. In antiepizootic work, general and specific prophylaxis is distinguished.
General prevention
- This is a series of constantly acting and universally carried out measures of veterinary-sanitary and organizational-economic nature aimed at the prevention of infectious diseases. It includes control over the movement of animals and livestock products, proper feeding, normal animal welfare, regular cleaning, disinfection of premises, territories, 30-day quarantine of newly arrived animals, timely cleaning, disinfection of manure, disposal (destruction) of corpses and other activities.
Specific prevention is a special system of measures aimed at preventing the appearance of a specific (specific) infectious disease. This includes timely timely diagnostic tests and immunization through the use of various biological products, mainly vaccines. It is carried out on a healthy livestock when it is necessary to protect it from one or another infectious disease. Such vaccines are called protective (preventive).
Effective biologics have been developed against most infectious diseases - vaccines that protect animals, prevent the occurrence of diseases and stop their further spread.
The vaccine is obtained from microbes or their metabolic products. According to the method of preparation, two main types of vaccines are distinguished: live and inactivated (killed).
A vaccine that protects animals from one infectious disease is called monovalent.
Associated vaccines allow the simultaneous formation of immunity against several diseases.
According to the method of introducing vaccines into a living organism, vaccinations are divided into parenteral, enteral and respiratory.
The parenteral method includes subcutaneous, intramuscular, intradermal and other methods of administration, bypassing the gastrointestinal tract.
In the enteral method, biological products are administered through the mouth individually or in a group manner with food or water.
The respiratory (aerosol) method of vaccination is that a biological product is administered into the respiratory tract by spraying, in the form of an aerosol.
Vaccinated animals must be monitored for at least 12-15 days.
Immunity after vaccination is formed for 10-15 days and lasts depending on the characteristics of the vaccine from 6 months to 1 year, and sometimes longer.
When clinically pronounced post-vaccination reactions and complications of such animals are immediately isolated from the general herd and a veterinarian is informed about them.
When organizing vaccinations, it must be borne in mind that vaccination of sick, weakened, depleted animals can lead to severe post-vaccination reactions and complications. In addition, in these cases, the immune system is not sufficiently strained, and animals can become ill in the future.
Biological factors (living pathogens, infection and infectious process)
Concept of infection. Under the infection 1 understand the penetration into the body of pathogenic (pathogenic) microbes. Their interaction with the body in specific environmental conditions, the response of a macroorganism to the action of pathogenic microbes, manifested by certain symptoms, is the basis infection process.
1 (From the Latin word inficio - I infect.)
In the infectious process, they play the role of: a microorganism - the causative agent of infection, a macroorganism in which the microbe manifests its vital activity, and an external environment that affects the properties of macro- and microorganisms.
The causative agents of the infectious process are pathogenic microbes, as well as filtering viruses that cause a number of diseases (measles, rubella, influenza, polio, smallpox, etc.). Viruses are apparently able to penetrate even through intact skin and mucous membranes.
Infectious disease is not caused by any pathogen. For example, microorganisms living on the skin and mucous membranes usually do no harm (the so-called saprophytes).
The causative agents of infectious diseases have the main property pathogenicity, or pathogenicity. Some microbes that are not pathogenic can, under certain conditions, acquire this property. So, with a general depletion of the body, saprophytes sometimes become pathogenic. On the other hand, a person can be a carrier of a pathogenic microbe and not get sick. For example, pathogens of diphtheria bacilli or meningococci can be found in the mouths of some people, and these people still do not get diphtheria or meningitis (the so-called healthy carcinoma). This is due to the properties of both the pathogenic microbe and the body's resistance.
In order for a pathogenic microbe to cause an infectious disease, it must have virulence, i.e., the ability to overcome the body's resistance and exhibit toxic effects. The degree of virulence of microbes depends on the properties of macro- and microorganisms. An increase in the virulence of microbes is observed during their passage (passages) through an animal organism susceptible to them. So, the virulence of streptococci increases dramatically due to repeated passages through the body of a rabbit.
The virulence of microbes increases due to their production of aggressins and antipeptolytic enzymes that suppress the immune properties of the body, as well as a propagation factor that increases tissue permeability. The latter is an enzyme hyaluronidase that breaks down hyaluronic acid - an integral part of connective tissue.
In other cases, conducting microbes through an immune system makes them less virulent.
When cultured on artificial media (with the addition of immune sera), the virulence of microbes decreases.
Changing the properties of microbes under the influence of environmental factors causing a weakening of their virulence can be used for practical purposes for the preparation of attenuated vaccines, with the help of which immunization of the body is more easily achieved.
Some microbes cause poisoning of the body due to the production and release of toxic substances by them - exotoxins. The latter easily diffuse from the body of bacteria, are absorbed and flood the entire body (the so-called bacterial intoxication), for example, with tetanus or diphtheria. In other cases, a bacterial infection proper occurs that causes the body to respond to the effects of the bacteria themselves, for example, with anthrax. However, it is not always possible to establish a clear line between these two types of toxigenicity. Finally, toxins can be released from the bodies of bacteria when they are destroyed - endotoxinsfor example typhoid endotoxins, cholera.
Exo and endotoxins are specific microbial products.
Non-specific substances that poison the body during the infectious process include the breakdown products of bacteria (for example, bacterioproteins, enzymes), as well as the products of cell metabolism and breakdown of tissues of the affected macroorganism (for example, proteinogenic amines). All of these substances, especially of microbial origin, can cause intoxication of the body.
A feature of infectious processes is their infectiousness. Depending on the source of infection and the pathways of microbes, human infectious diseases arise as a result of direct contact with patients (through mucus, sputum), through air and nutrients, or through intermediate hosts that transmit the infection, for example, ticks, bugs, fleas, mosquitoes (food encephalitis, tularemia, typhus, relapsing fever, malaria).
Entrance gate of infection. These are the ways in which microbes enter the body with air, nutrients, water, through contact with a sick person or an insect bite. The places where microbes enter are the respiratory tract, the gastrointestinal tract, damaged skin, mucous membranes, tonsils, excretory ducts of the glands, etc. The place where microbes enter is of great importance in the development of infectious diseases. So, cholera vibrio enters the body through the mouth and does not penetrate the skin. Gonococci act only through the mucous membranes of the genitourinary tract or the mucous membrane of the eye. Even for those microbes in respect of which there are several ways of penetration into the body, the method of penetration is of great importance in the onset and development of the disease. For example, anthrax bacilli are less virulent when ingested through the skin than if they penetrate the lungs or intestines.
Entrance gates are not only the starting point for the penetration, spread or reproduction of microbes, but also an extensive reflexogenic zone. An infectious agent or toxin, coming in contact with the receptor apparatus of the affected tissue, can cause reflex reactions. For example, the endotoxin of Flexner's dysentery, acting on the interoreception of the small intestine, causes a change in blood circulation in the large intestine, a drop in blood pressure, and respiratory failure.
Body interaction with infection. The penetration of pathogenic microbes into the body can have various consequences.
1. Pathogenic microbes can settle on its integument or in various organs, multiply and excrete from the body. However, in this case, the visible reaction of the body and disabilities is not observed. In these cases, the body is like a reservoir for microbes that have penetrated into it (bacterial carriage). Settling in certain places of the body, microbes can even have great physiological significance. For example, B. coli in the colon play a role in the synthesis of prostatic groups of coenzymes and vitamins (e.g., B12). But the same microbes become pathogenic when they enter the gallbladder.
2. Hidden, or latent, infection arises as a result of infection, but causes only small deviations in the vital functions of the body, which is gradually released from microbes due to their isolation or the development of immunity. Such infectious diseases ("asymptomatic") are sometimes observed when infected with typhus or typhoid fever, scarlet fever and other infections. In viral infections, there may also be a latent course, for example, the so-called inapparent infections (measles in mice, typhus in guinea pigs). Finally, in the course of the development of the infectious process, asymptomatic phases may occur. These include, for example, the incubation period, i.e., the time from the moment of infection to the onset of the disease, as well as individual periods of the asymptomatic course of the disease. Actually latent infections can be attributed to some forms of tuberculosis, which are characterized by an asymptomatic course, but the body responds to extracts from tubercle bacilli and often foci of infection can be found in it (for example, in the lungs). With injuries and other pathogenic effects, a latent infection can become apparent.
3. The penetration of pathogenic microbes causes a widespread infectious disease. It is characterized by certain symptoms in the form of an increase in temperature, changes in the morphological and chemical composition of blood, more often an increase in the number of leukocytes, an acceleration of the erythrocyte sedimentation reaction, a decrease in the activity of a number of enzymes, and antibody production. Infectious diseases are often characterized by damage to various organs, the development of the inflammatory process in them. In this case, the type of inflammation depends on the pathogen and the condition of the body. For example, streptococcal and staphylococci usually cause purulent, tuberculous infection - productive, measles and scarlet fever - serous inflammation. The localization of inflammation is also different, for example, with cholera - in the small intestines, with dysentery - in the large intestines, with croupous pneumonia - in individual lobes of the lung. Generalization of infection is possible in four ways (by continuation, through contact, by the lymphogenous or hematogenous route).
The development of the infectious process most often causes a weakening of the body’s adaptability, a feeling of malaise or pain, limitation or disability. The interactions of the microbe-pathogen and the body are very diverse and are determined by many factors of the external and internal environment. As the infectious process develops, the nature of the interaction also changes. The fate of the infection depends not only on the number and virulence of microbes, but also on the state of the body, its immunity, susceptibility to this infection, nutrition, climate and other external influences.
Infection spread. Affecting the body as a whole, pathogens at the same time cause characteristic pathological changes in individual organs, for example, with gonorrhea, pneumonia or typhoid fever.
From the infected focus, microbes can penetrate into other organs and tissues, causing the appearance of secondary foci in them. An example is the transfer of pyogenic cocci, accompanied by the occurrence of purulent processes in different parts of the body ( pyemia) Infectious pathogens can flood the blood ( bacteremia) and, spreading throughout the body, simultaneously affect many organs (phenomena sepsis).
Ways to isolate germs different from the body. Most often they are secreted by the intestines (mainly with intestinal infections). Microbes that get into the blood are often excreted in urine (for example, with typhoid fever, gonorrhea), milk (with common septic diseases), saliva (rabies virus) and sputum (for respiratory diseases).
Poisonous substances secreted by snakes, scorpions and bees cause edema, tissue necrosis, and when exposed to the central nervous system - often nausea, vomiting, severe shortness of breath, up to paralysis of the respiratory center. The active principle of these toxic substances, apparently, are compounds such as histamine, acetylcholine and enzymes, from the contact of which active polypeptides are formed, such as bradykinin, etc.
Fungi can cause skin diseases (ringworm, scab, blastomycosis, etc.) and internal organs (actinomycosis).
Infectious diseases arise as a result of the penetration of bacteria, viruses, rickettsia, fungi, mycoplasmas and chlomidia into the human body. Diseases caused by protozoa, helminths, insects are parasitic, but in their structure they can be attributed to infectious.
The development of any infectious disease begins with the penetration of the pathogen into the human body. In this case, a number of conditions are necessary: \u200b\u200bthe state of the macroorganism (the presence of receptors to which the microbe will be fixed; the state of immunity, etc.) and the state of the microorganism. The most important properties of the infectious agent are taken into account: pathogenicity, virulence, toxigenicity, invasiveness.
Pathogenicity is the ability, fixed genetically, of a microorganism to cause a specific disease. It is a species trait, and bacteria can cause only certain clinical symptoms. By the presence or absence of this sign, all microorganisms are divided into pathogenic, opportunistic (cause the disease under any adverse conditions) and non-pathogenic, or saprophytes.
Virulence is a degree of pathogenicity. For each colony of pathogenic microbes, this property is individual. Virulence is judged by the severity and outcome of the disease that this pathogen causes. In laboratory conditions, it is measured by the dose that causes in half of the experimental animals either the development of the disease or death. This property is not stable, and virulence can vary in different colonies of bacteria of the same species, for example during antibiotic treatment.
Invasiveness and adhesiveness - the ability of microbes to penetrate into human tissues and organs and spread to them.
This is explained by the presence of various enzymes in infectious agents: fibrinolysin, mucinase, hyaluronidase, DNase, collagenases, etc. With the help of them, the pathogen penetrates all the natural barriers of the human body (skin and mucous membranes), contributes to its vital activity under the influence of the body's immune forces.
The above enzymes are present in many microorganisms - pathogens of intestinal infections, gas gangrene, pneumococci, staphylococci, etc., and provide further progression of the infectious process.
Toxigenicity - the ability of microorganisms to produce and secrete toxins. There are exotoxins (protein) and endotoxins (non-protein).
Exotoxins are protein toxins, substances that are the products of the vital activity of bacteria and secreted by them into the environment. Basically, exotoxins form gram-positive bacteria, for example, pathogens of diphtheria, tetanus, botulism, gas gangrene, scarlet fever, meningococcal infection. These substances have enzymatic properties, are highly specific and affect certain organs and tissues, which forms certain symptoms of the disease. For example, the tetanus pathogen selectively acts on the motor centers of the spinal cord and medulla oblongata, the Shigella Grigoriev-Shiga toxin affects the intestinal epithelium cells. Exotoxins cause disturbances in the oxidation processes in cells. They are sensitive to high temperatures, under certain conditions (formalin treatment) they lose their toxigenic properties, retaining antigenic properties (they can form antitoxins when introduced into the body). These detoxified exotoxins are called toxoids, which are widely used to immunize against tetanus, diphtheria, and other infections.
Endotoxins are firmly connected to the microbial cell and are released when it is destroyed. Mostly found in gram-negative bacteria. In their structure, they are complex carbohydrate-lipid-peptide complexes. They have less specificity and selectivity, resistant to high temperatures, less toxic than exotoxins.
For the development of an infectious disease, it is necessary that the pathogen, possessing all of the above properties, penetrates the human body. The place of entry is called the entrance gate. The gates of infection for each pathogen are always constant. Some microorganisms penetrate the skin (malaria, typhus, erysipelas, cutaneous leishmaniasis); others - through the mucous membranes of the upper respiratory tract (tonsillitis, measles, scarlet fever, acute respiratory viral infections), the gastrointestinal tract (dysentery, typhoid fever, cholera), genitals (syphilis, gonorrhea). Certain microbes can enter the body in several ways (the causative agent of AIDS, plague, viral hepatitis). The clinical manifestations of the disease sometimes depend on the site of the infection gate. Thus, if, for example, the causative agent of the plague penetrated through the skin, then there is a bubonic or skin-bubonic plague, if through the respiratory tract - then the pulmonary. At the site of penetration of the microorganism, a focus of inflammation is formed. Then, from the entrance gate, bacteria spread through the body in various ways. If the pathogen enters the lymphatic vessels and is spread through the organs by lymphatic current, then this is the lymphogenous pathway of distribution. If the pathogen penetrates into various organs and tissues through the blood vessels, then this is the hematogenous pathway. The penetration and circulation of infectious agents in the bloodstream is called bacteremia (for example, typhoid fever), viremia (with influenza), parasitemia (with malaria).
The microorganism can also remain at the site of introduction, in which case toxins produced by bacteria act on the body. Toxinemia occurs, i.e., toxins circulate in the bloodstream. This is observed with scarlet fever, tonsillitis, diphtheria, gas gangrene, botulism, etc. Another important characteristic of the causative agent of an infectious disease is tropism, or its sensitivity to certain tissues, organs, and systems. For example, the pathogen affects the cells of the respiratory tract, dysentery - the intestinal epithelium, mumps, or "mumps" - the tissue of the salivary glands.
In response to the introduction of an infectious agent, the body reacts with the formation of protective reactions aimed at limiting and completely freeing the body from the pathogen and also at restoring the impaired functions of the affected organs and systems. The outcome of the interaction depends on a number of conditions: the state of local protection (intact skin, mucous membranes, the state of microflora), the functioning of specific and non-specific protection factors (state of immunity, the production of protective substances), the number of penetrated microbes, the degree of their pathogenicity, the state of nervous and endocrine are important human systems, age, nutrition.
If the protection system works well, then the infectious process may not develop further, but remain at the site of penetration, which does not lead to clinical symptoms. If the body is sensitive to this pathogen and the protective factors are imperfect, then infectious agents and their toxins penetrate the blood, contributing to the development of an infectious disease. Thus, the state of the human body, especially his the immune system.
The immune system (immunity) is a complex of processes that are aimed at the constancy of the internal environment of the body, preventing the penetration of infectious and other foreign agents. The central organs of immunity are the thymus gland (thymus), red bone marrow. Peripheral organs - spleen, lymph nodes, accumulations of lymphoid tissue in the intestine (Peyrea plaques). The functions of the immunity system: recognition of foreign agents (foreign antigens) with subsequent response, which consists in neutralizing, destroying and removing them from the human body.
The degree of functioning of the immune system and non-specific protection factors (the integrity of the skin and mucous membranes, the presence of protective substances in body fluids, etc.) depends on the age of the child, on which the infection process has its own characteristics in different age groups.
Infectious diseases
Among the many diseases to which a person is exposed, there is a special group of diseases that are considered to be infectious or infectious.
Infectious diseases are diseases caused by a living pathogen that have the ability to be transmitted from a sick person to a healthy one, causing epidemics. As a rule, these pathogens are microorganisms - organisms that cannot be seen with the naked eye, but only with the help of more or less powerful microscopes.
But not all microorganisms pose a threat to human health. Some microbes can be located inside the human body without causing disease and even assisting vital processes such as digestion. According to this, all microbes on the globe are divided into three large groups by pathogenic microorganisms, that is, those that cause diseases can be:
Bacteria (cholera, sepsis, tuberculosis);
Viruses (influenza, hepatitis, HIV);
Mushrooms (skin mycoses);
Protozoa (dysentery, malaria)
Bacteria
Bacteria are unicellular pre-nuclear organisms. On Earth, there are more than three thousand species. They have microscopic sizes (from 0.2 to 1 μm). The morphology of bacteria is quite diverse, according to this they are classified in a certain way according to shape and ability to form groups. So, the following forms of bacteria are distinguished.
1. Monocoque. Groupings do not form. They have a spherical shape of the cell. Truly pathogenic forms are rarely found among them. The most common representatives of monococes are micrococcus orange (Micrococcus aurentiacum) and micrococcus white (Micrococcus album), which, if propagated, form orange and white spots on food.
2. Diplococci. There are several varieties. More often, a combination of two bacterial cells of spherical shape, covered with a mucous membrane, is found. Nitrogen-fixing brown nitrogen (Azotobacter croococcum), the causative agent of pneumonia (Dyplococcus pneumonius) have this form. There are also combinations of two cells that look like coffee beans. These include causative agents of gonorrhea (Neiseria honored) and meningitis (Neiseria miningitidis).
3. Streptococci. Spherical cells form long chains. Among them there are both non-pathogenic, for example, those that cause souring of milk (Streptococcus lactis), and pathogenic, which cause diseases of tonsillitis, scarlet fever, and rheumatic heart disease. Characteristic feature they is that in the process of life they secrete a c-reactive protein that has hemolytic properties, i.e. those that destroy hemoglobin (Streptococcus piogenes).
4. Sarcins. Several spherical bacterial cells form small groups. A characteristic feature of this type of bacteria is the formation of spores and extremely rapid reproduction. Among the representatives are Sarcina flava, which forms yellow spots on food products, and Sarcina urea, which decomposes urine.
5. Staphylococci. There are also pathogenic and non-pathogenic forms. For example, Staphylococcus aureus (Staphylococcus aureus) forms golden colonies in a nutrient medium and does not pose any direct threat to human health. However, there are a number of extremely dangerous staphylococci that cause severe inflammation: scarlet fever, sepsis. A colony of staphylococci is always a large collection of spherical cells. A characteristic feature of this group is its strong mutagenicity - the ability to form new forms.
6. Cocobacteria. Extremely widespread in the environment is a group of bacteria. Cells are very small sticks that are sometimes difficult to distinguish from micrococci. Thus, Pseudomonas lives in water and soil, which plays an important role as reducers. IN gastrointestinal tract conditionally pathogenic Escherichia coli (Esherichia Coli) inhabits humans and animals, which, on the one hand, helps digestion, but, on the other hand, some of its forms can cause cholecystitis, pancreatitis. Salmonela tiphi, which causes typhoid, and Proteus vulgaris, an anaerobic, which causes a painful state of cavities (for example, maxillary), can be distinguished among pathogens.
7. Bacilli. Evolutionarily more advanced forms of bacteria, have a cylindrical shape and form spores. In addition, they can always use nutrients from the environment. The bacillary form is Bacilus subtilis - hay bacillus, which multiplies rapidly in warm tea, Bacilus turingiensis - a bacterium that is of great importance for the development of environmentally friendly insecticides. It secretes a protein substance that causes paralysis of the intestinal apparatus of insects.
9. Streptobacilli. Like streptococci, they form long chains of their cells. Pathogenic streptobacilli are found. So, Streptobacilus antracis is the causative agent of anthrax.
10. Clostridia. They have a fusiform shape, they are characterized by an anaerobic way of breathing. That is why most clostridia are pathogenic microorganisms. Clostridium tetani - the causative agent of tetanus, Clostridium botulinum - causes severe digestive disorders - botulism, Clostridium septicum - the causative agent of gas gangrene. Clostridium perfringens is an indicator of fecal soil contamination. Living in the body, it enriches it for enzymes, but in case of diabetes, it can cause gangrene.
11. Vibrions. Relate to forms that are sometimes called sinuous. They are sticks bent by less than a quarter of a circle, slightly trembling. A typical representative of vibrios is the causative agent of cholera Vibrio cholera, which sometimes forms blue colonies. Its feature is that it is the only one that tolerates an alkaline medium (pH greater than 7).
14. Mycoplasmas. Interesting bacteria because they do not have a cell membrane. ) X can be considered as a transitional form between viruses and cellular life forms. A characteristic feature is that they are completely unable to exist outside the host cell. Mycoplasmas are mainly represented by pathogens of plants and cattle.
In addition to the classification of bacteria according to the shape of cells, a very important systematic feature is their color. All methods for classifying bacteria by coloration are based on their uneven internal chemical composition. The most generalized classification method is Gram stain. This method allows you to divide the entire huge number of bacterial organisms into two groups: gram-positive (turn purple after staining) and gram-negative (turn red after staining).
The practical significance of this systematics lies in the unequal sensitivity of gram-positive and gram-negative bacteria to antibiotics. So, gram-positive bacteria are more sensitive to antibiotics of the penicillin series, and gram-negative - to antibiotics of the gentomycin and streptomycin series. This determines the methods of treatment of infectious diseases.
There is an interesting feature of the spread of bacteria different forms in the human body. By the percentage ratio between the types of microorganisms, one can determine the predisposition to a particular disease, prevent complications, and start treatment on time. A microflora sample is taken from the oral cavity, and its analysis can be easily done even at home with a microscope.
So, if streptococci and staphylococci dominate, this indicates respiratory diseases. If rod-shaped forms prevail (bacilli, streptobacilli, etc.) - diseases are possible gastric tract. The appearance of diplococci is a sign of a disease of the genital organs, candida (branched chains of spherical bacteria) is an indicator of dysbiosis, possibly thrush, and stomatitis develops. Spirochetes are satellites of the inflammatory process in the oral cavity. If all bacteria are in approximately the same amount, there is no reason to worry.
Viruses
The second group of common pathogens of human diseases are viruses. A virus is an autonomous genetic unit capable of reproduction (reduction) only in the host cell. Viruses can be considered as substances outside the cell. But, getting into the host’s body, they begin to behave like living things.
The structure of the virus is quite simple. It consists of a segment of a nucleic acid (DNA or RNA) and protein molecules that perform the function of a membrane (Fig. 49). The protein coat is enzymatically active; it ensures the attachment of the virus to the host cell. Viruses are specific, they affect not only a specific species of animals, plants or humans, but also certain host cells, so the polio virus infects only nerve cells and does not harm others.
Depending on the type of nucleic acid, DNA genomic and RNA genomic viruses are distinguished. DNA genomic pathogens include hepatitis B, chickenpox, shingles. RNA genomic viruses cause influenza A, B, C, measles and other diseases. A special group of viruses is made up of the so-called retroviruses, the representative of which is the well-known HIV - human immunodeficiency virus. HIV infects immune cells. In case of infection, severe AIDS disease occurs.
The mechanism of action of viruses is that when they enter the body, they adsorb into the host cell. Here there is a transition from an inert (crystalline) state to an active one. Next, the virus discards its envelope, freeing a piece of nucleic acid, which is embedded in the genetic apparatus of the cell. The synthesis of the components of the virus (nucleic acids, proteins). Newly formed particles break the cell and go outside, damaging nearby cells.
Vital activity of some viruses is quite specific. They can enter the human body, integrate their nucleic acid into the DNA or RNA of the host cell. But, remaining in the cell, they are in a kind of symbiosis (the phenomenon of virogenesis) and do not manifest themselves in anything. Thus, the vital activity characteristic of retroviruses.
It is known that the main cause of cancerous tumors is the action of just such viruses. A newly formed gene that has not manifested itself for a long time, during nervous stress, exposure to radiation, carcinogens, begins to function actively and causes the cell to synthesize mitotic division stimulants. The appearance of excess proteins as a result leads to the formation of cancerous tumors.
Among other features of the vital activity of many forms of viruses (for example, the causative agent of influenza), the so-called antigenic drift, mutations that occur in the pathogen every 2-3 years, should be noted. The content of this process is to replace some part of the gene. The whole gene is replaced after 8-11 years. The significance of this process is to counteract specific immunity. Interestingly, one virus, once in the human body, protects it from the penetration of other viruses. This phenomenon is known as virus interference.
A special group of microorganisms are phages - bacterial viruses. They are built more complicated, under an electron microscope it can be seen that they have the shape of a comma or clubs with sizes of 5-6 nm. They consist of a head, a shaft, inside which there are special contractile proteins, and several processes.
The phage infects both pathogenic and non-pathogenic bacteria, therefore it was believed that it can be used to treat infectious diseases. But it turned out that inside the human body, the phage loses its activity. Therefore, it can be used only for the diagnosis of bacterial infections.
Mushrooms
The body of the fungus (mycelium) can consist of one, highly branched cell, or many. The main product of the vital activity of fungi is urea. Mushrooms reproduce extremely intensively, as a rule, by peculiar spores or budding.
Protozoa and worms
Another group of pathogens of infectious diseases are protozoa and worms.
The simplest animals that cause diseases include dysentery amoeba, coccidia, and sporozoans. The body of the simplest animals consists of only one cell, performing all the functions of an entire organism. So, dysenteric amoeba resembles a piece of protoplasm, constantly changes its shape, and can actively move. Once in the human body, it causes a serious illness of the digestive system - dysentery.
The cause of the disease is always the penetration of the pathogen into the human body if hygiene rules are not observed, violation of cooking technology, contact with patients, etc.
