SUSCEPTIBILITY, to an infection — ability of an organism to react to implementation of infectious agents development of a disease, inapparantny (asymptomatic) infection or a mikrobonositelstvo. Distinguish V. specific, inherent in all individuals of this or that look, and also the individual, concerning only certain representatives of this look. Both specific, and individual V. can be full, high, moderately expressed, weak or it completely is absent. It is shown in relation to certain types, serological and biochemical, to types of pathogenic and conditionally pathogenic microorganisms century. Degree and specific manifestations of V. to this or that activator can change in the course of evolution of this look — the recipient or the agent infecting it.
It is accepted to understand predisposition of certain individuals to developing at them of an infection or a mikrobonositelstvo under the influence of the infecting agent as individual V. Specific manifestations and individual V.'s degree of live organisms, including the person, are defined by this or that degree of their immunity acquired as a result of earlier postponed infection of the same etiology, and also preventive inoculations with pi wives py reactivity, existence of associated diseases.
Microbes, pathogenic for different types of animals, birds, fishes, plants, quite often are not able to cause an infection or a mikrobonositelstvo in the person. The specific susceptibility in relation to various microorganisms is genetically caused and considerably is defined by features biochemical, structure of cells and body tissues. The threshold infecting dose of pathogenic microorganisms depends on them virulence (see). Is known the fact that the strains of tulyaremiyny bacteria circulating in separate geographical zones can significantly differ on degree of the virulence thanks to what (in combination with a certain V. and reactivity of certain people) the clinical picture of diseases of a tularemia differs in considerable variability.
Specific V. of people to plague is general though individual V. can significantly decrease thanks to use of specific inoculations or performing chemoprophylaxis by the streptomycin suppressing development of the plague bacteria which already got into an organism.
Specific, and also individual V. should be considered in close connection with the specific mechanism of infection, entrance gate, through to-rye the infectious agent gets into an organism. These indispensable conditions of V. of the person to various infections in some cases differ in high specificity. So, e.g., the person gets sick with dysentery only on condition of penetration of shigellas through a digestive tract, but not in any other way. At the same time concerning a number of infectious diseases (e.g., a malignant anthrax) V. is shown irrespective of entrance infection atriums and can cause considerable polymorphism of specific clinical displays of a disease. The disease of botulism can arise as as a result of receipt of the activator and its exotoxin through a digestive tract, and at their penetration into an organism through respiratory tracts. Once the postponed infectious disease in some cases creates immunity to action of the same agent. After such diseases as natural smallpox, measles, V. to reinfection sharply decrease owing to what recurrent diseases represent a big rarity, the organism gets strong, lifelong immunity (cm). At the same time once the postponed acute infectious disease can be followed by such its V.'s changes, adverse for an organism, to the infectious agent, to-rye create premises for development of a recurrence (a typhoid, a typhinia, dysentery, etc.), and also the long and chronically proceeding forms of infectious diseases (e.g., a brucellosis). In these cases allergic reorganization of an organism as it takes place at recurrent forms of an ugly face is shown.
The age of the person also influences his V. U of children note higher, than at adults, V. to droplet infections (measles, scarlet fever, whooping cough, diphtheria). This age feature of V. to droplet infections affects also the clinical course of infectious diseases. It is known that the meningococcal infection proceeds, as a rule, heavier at children's age. Children of the first dvukhtrekh months of life have a transfer to milk of mother of nek-ry antibodies, including diphtheritic antitoxin that (despite the imperfection of many mechanisms of immunity inherent to children of this age) interferes with infection with diphtheria. At the same time V. to a number of infections at people of advanced and senile age also has the features, napr, the long (torpid) course of a pulmonary tuberculosis at people with the lowered reactivity of an organism of these age groups.
Genetic bases of individual V. of the person to infections remain for the present poorly studied. The role of a thymus, immunoglobulins of different classes, factors of cellular immunity is investigated. The individual V.'s changes created by preventive inoculations can fluctuate in very wide limits that depends first of all from reactivity of an organism (see), extents of development of its protective mechanisms, immunogene properties of a vaccine.
Such factors as overcooling or overheating of an organism, ionizing radiation, action of immunodepressants exert impact on the individual V.'s level of people to infections. The raised V. of people to infectious diseases can be caused by allergic processes.
The numerous facts of higher individual V. of people to infectious diseases are determined when is available inborn or acquired hypo - and agammaglobulinemia (see) and other immunodeficiency (see. Immunological insufficiency ). Changes of conditions of food of the person (including a nutritional dystrophy, hypo - and avitaminosis), disturbances of hormonal regulations can raise V. of people to infections.
Bibliography: Burnett F. M. Cellular immunology, the lane with English, M., 19 71, bibliogr.; Boyd U. Fundamentals of immunology, the lane with English, M., 1969, bibliogr.; Boone and K. V N. Progress and problems of clinical immunology of infectious diseases, M., 1972; Efroimson E. P. Immunogenetics, M., 1971.
K. V. Bunin.