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Flu — the acute viral disease which is characterized by a short incubation interval, the expressed general intoxication, catarral changes of respiratory tracts and tendency to bacterial superinfections.
Now along with an influenzal virus about 200 activators causing grippopodobny diseases are known. Among them there are parainfluenza viruses, adeno-, rino-, reo-, entero-, respiratory and syncytial viruses, mycoplasmas, chlamydias, pneumococci, meningokokk, legionella, etc. All these diseases are known as acute respiratory diseases of mainly virus nature. Annually, with cold weather approach ORZ number considerably raises and on this background the flu epidemic at which among urban population within 3 — 4 weeks 20 — 25% with fluctuations from 6 — 8 to 30 — 35% get sick with flu on average develops.
Etiology. The causative agent of flu — RNA-viruliferous. 3 serological options of influenza viruses are known — And, In and S. Naiboley characteristic of an influenza virus is unique variability of its surface antigens — hemagglutinin and a neuraminidase. In recent years it is established that the reason of recurrent diseases and repetition - ny epidemics is the specified variability of a virus. Under natural conditions it is inherent in an influenza virus of type A and happens to a certain sequence. Antigens of a virus of V type change in much smaller degree and not systematically, variability of antigens for a virus C is not registered.
Epidemiology. Flu — one of the most widespread diseases, periodically gets pandemic distribution. During the periods between pandemics almost annual epidemic flashes are observed, and in interepidemic time separate sporadic cases meet.
Emergence of pandemics is connected with emergence of a new subtype of an influenza virus And with significantly changed in comparison with the previous one, and even both surface antigens. During the periods between pandemics slightly changed options of an influenza virus of type A are the reason of almost annual epidemic flashes. The influenza virus of type B causes epidemics much less often, in 4 — 6 years, a virus C — sporadic cases and very seldom small epidemic flashes.
Pathogeny. An infection source — the patient. On the mechanism of transfer is droplet infection. Infection occurs at hit of a virus on mucous membranes of respiratory tracts. Here it is implemented into a cylindrical epithelium and alveolar cells where finds optimum conditions for development. During this period the virus can be found in blood. Clinical manifestation of symptoms is preceded by a phase of the hidden interaction of a virus with a susceptible cell in which there is a reproduction and accumulation of the infectious beginning. Owing to essential disturbances of a metabolism the infected cells perish with release of both virus particles, and nonspecific toxic substances (biogenic amines — a histamine, serotonin, acetylcholine, and also kinin, autoallergens, etc.) . The released virus partially is thrown out external environment during cough, sneezing and conversation, the part it is implemented into even untouched cells, but a significant amount gets into blood, creating, on the one hand, a virusemia, with another — providing development of a syndrome of the general intoxication. Unlike other respiratory viral infections the activator reproduction at flu occurs much quicker. From here short incubation interval and suddenness of developing of an illness.
Impact of a virus and the nonspecific toxic substances coming to blood from the center of primary fixing of a virus on the important centers which are carrying out neurovegetative, neuroendocrinal and neurohumoral regulation in an organism, located in a diencephalon zone where as a result of the maximum vascularization high concentration of toxic products is created is the cornerstone of the mechanism of development of the general intoxication. As a result of impact of toxic substances on sensitive receptors of a meninx, vessels of bark and a diencephalon, and also frustration of a cerebral hemodynamics there is a headache and other symptoms of the expressed general intoxication: dizziness, general weakness. The irritation of area of a hypothalamus "leads to development of functional shifts in a metabolism, a hormonal range of blood, activity of mediators and enzymes. Direct and reflex influence of a virus and toxic products on the central nervous system involves change of permeability of capillaries, it breaks exchange processes, education and dynamics of cerebrospinal fluid, microcirculation and a hemodynamics in general. Now existence of a virusemia, toxaemia and their value in a pathogeny of flu does not raise doubts, but the virus not only is in blood and is brought by it in various bodies and fabrics, it collects in them (in a brain, kidneys, a liver), being sometimes the reason of inflammatory reactions (meningitis, an encephalomeningitis, etc.). Weight of defeat of a nervous system depends both on features of the activator, and on an initial condition of a macroorganism, its nervous system, the general resistance, existence or lack of a sensitization, the centers of persistent infection.
Penetration into upper respiratory tracts and alveoluses and primary fixing of an influenza virus into them cause continuous development of catarral changes of respiratory tracts.
Development and the course of a disease are influenced significantly by bacterial flora, causing secondary damages mainly of airways, is more rare than okolonosovy bosoms and kidneys.