Infectious disease prevalent worldwide caused by various microorganisms. “Infectious” disease known since ancient times, information about them can be found in the most ancient monuments of writing in the Indian Vedas, Ancient China and Ancient Egypt. Descriptions of some infectious diseases, such as dysentery, tetanus, erysipelas, anthrax, viral hepatitis, etc. can be detected in the writings of Hippocrates (460-377 BC). In the Russian Chronicles of the infection, described under the name of epidemic, endemic morovich diseases, emphasizing the main feature – mass, high lethality and rapid prevalence among the population. Described devastating epidemics and pandemics of infectious diseases. It is known that in the Middle ages was raging plague (“black death”), which died out a third of Europe’s population, and around the world from the plague in the fourteenth century killed more than 50 million people. During the First world war was the influenza pandemic (“Spanish flu”), which affected 500 million people, 20 million of them died. For a long time about the cause of infectious diseases were not known, believed that these diseases arise in connection with the “miasma” – poisonous exhalations of air. This teaching in the sixteenth century gave way to the doctrine of “contagia” (Trekstore).Infectious diseases – a large group of human diseases arising from effects on the body of viruses, bacteria and protozoa. They develop in the interaction of two independent biological systems of microorganism and of microorganism in the conditions of influence of external environment, and each of them has its specific biological activity.

Infection is the interaction of the microorganism with the microorganism under certain conditions the external and social environment, resulting in evolving pathological, protective, adaptive, compensatory responses, which are combined in the infectious process. The infectious process is the nature of infectious disease and can manifest at all levels of organization of Biosystems is submolecular, subcellular, cellular, tissue, organ, organism.

However, not every impact of the pathogen in the organism causes the disease. An infectious disease occurs if there is a violation of the functions of the body and the appearance of the clinical picture. Thus, infectious disease is the extreme degree of development of infectious process. If the penetration of the pathogen in the body does not occur the formation of the clinical picture, we speak of a healthy carrier that can be in children with residual specific immune system or in people born with natural immunity. There is also reconvalescent carriage occurring during convalescence from infectious diseases. Depending on conditions of infection, the properties of the infectious agent, state of microorganism (susceptibility, the degree of specific and nonspecific reactivity) describes several forms of interaction of microorganisms with the human body.

Symptomatic forms (clinically manifested) can be divided into acute and chronic. Also distinguish typical, atypical and fulminant forms generally ending in death. Severity is divided into mild, moderate and severe forms.

In the acute form is clinically manifested infection, the pathogen stays in the body for a short time. For this form characterized by a higher intensity of selection patients with pathogens in the environment that creates high infectiousness of patients. Many infectious diseases are acute, such as plague, smallpox, scarlet fever. Other and in acute and chronic brucellosis, hepatitis b, dysentery.

The chronic form of the disease is characterized by a longer stay of the pathogen in the body, frequent exacerbations and remissions of the pathological process and in case of timely treatment – favorable outcome and recovery, as in the acute form.

Recurrent disease due to infection by the same infectious agent called a reinfection. If there is an infection to others infectionim agent, to recovery from the disease, it is called superinfection.

The bacteriocarrier is a process that is asymptomatic in the acute or chronic form. Pathogens are present in the body, but the manifestation process is not happening, and outwardly the person remains healthy. In the body are detected immunological changes and functional they morphological disturbances in the organs and tissues that are typical for this disease.

Important epidemiological importance of the subclinical form of the infection, as these patients are a reservoir and source of pathogens while maintaining the working capacity and social activity, which complicates the epidemiological situation. However, the high frequency of subclinical forms of certain infections (dysentery, meningococcal infection, influenza, etc.) contributes to the formation of massive immune interlayer among the people, that to a certain extent stop the spread of these infectious diseases.

Purulenta (latent) infection occurs as a result of prolonged asymptomatic interaction of a macroorganism with microorganisms. At its core, is a chronic infectious disease with benign course, is found in such diseases as hepatitis b, herpes infection, typhoid fever, cytomegalovirus infection, and more. . This form is more common in children with reduced cellular and humoral immunity, while an infectious agent is or defective condition, or in a particular stage of their life (L – form). The formation of L – forms occurs under the influence of immune protective forces of an organism and medicines (antibiotics). Formed atypical strains change all the properties of the microorganism.

Pathogens latent infection circulating inside host cells (intracellular parasitism) and in the environment are not highlighted. But under action of adverse factors (thermal effects, comorbidities, trauma, blood transfusion, etc.) latent infection can go to the island. The pathogen takes its usual properties.

Essentially a new form of interaction between infection with the human body is a slow infection. It is characterized by a long (several years) incubation period – the stage at which the disease is not present. At the same time, the disease steadily progressing with the development of serious disorders in many organs and systems (most often in the nervous system), and often there is death. For this type of diseases include: AIDS, congenital rubella, chronic active hepatitis with transition to cirrhosis.

Infectious diseases arising from infection by organisms of the same species are called monoinfection. When infected with bacteria of different types – combined or extincti. One of the variants of mixed infection is a secondary infection, in which the already existing disease associated new.

Infectious process may occur due to the activation of saprophytic microflora, i.e. those microbes that permanently live on the skin and mucous membranes. In these cases, talking about endogenous or auto-infection, which most often occurs in debilitated children with chronic diseases, in children long-term treated with antibacterial or cytostatic (suppressing the immune system) therapy.


Infectious diseases occur as a result of penetration into an organism bacteria, viruses, Rickettsia, fungi, Mycoplasma and chlamidia. 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. This requires a number of conditions: the state of the organism (presence of receptors that will be considered as the germ; the condition of immunity, etc.) and condition of the microorganism. Considered the most important properties of the infectious agent: pathogenicity, virulence, toxigenicity, invasiveness.

Pathogenicity is the ability of a fixed genetically, of a microorganism to cause a certain disease. The species is a symptom, and bacteria can be made only to certain clinical symptoms. The presence or absence of this symptom all microorganisms are divided into pathogenic, conditionally pathogenic (cause disease when unfavorable conditions) and non-pathogenic or saprophytes.

Virulence is degree of pathogenicity. For each colony of pathogenic microbes is a property individually. About virulence judged according to the severity and outcome of the disease this pathogen causes. In the laboratory is measured by the dose causing half of the experimental animals or the development of the disease, or death. This property is not stable, and virulence may vary among different colonies of bacteria of the same species, for example during antibiotic treatment.

Invasiveness and adhesiveness – the ability of microbes to penetrate into the tissues and organs and spread to them.

That is due to the presence of infectious agents of various enzymes: fibrinolysin, mucinase, gialuronidaza, Ankasa, collagenase etc. With them, the pathogen enters through natural barriers of the human body (skin and mucous membranes), contributes to their livelihoods under the impact of the immune forces of the body.

The above enzymes are available from many microorganisms – causative agents of intestinal infections, gas gangrene, pneumococcal, Staphylococcus, etc. – and provide further progression of the infectious process.

Toxigenicity – the ability of microorganisms to develop and produce toxins. There are exotoxins (protein) and endotoxins (non-protein.

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