Infection - the state of contamination of the organism, manifested disease or hosting (hosting, virusological, parasitological).
On the development of infectious process is influenced by the following factors: pathogenic properties of the pathogen (virulence), the degree of contamination (dose microbe) and the status of resistibility of organism (immunity).
Pathogenic microbe properties due to a number of substances generated in the microbial cell. Many microorganisms produce toxinsthat are released into the environment during their life - exotoxins [diphtheria Bacillus, the bacilli of gas gangrene, tetanus, botulism bacteria dysentery (view Grigorieva - Sigi)], and released during the destruction of microbial cells - endotoxins. Some pathogenic microorganisms produce enzymesthat destroy red or white blood cells (hemolysins, leukocidin), causing the clotting of blood plasma (coagulase), or, conversely, preventing the collapse of plasma (fibrinolizin). In addition, there are microbes that produce enzymes that cleave proteins and carbohydrates.
Reproduction and the activity of the microbes in the body stimulates the protective mechanisms: increased specific activity of phagocytes, develop immune responses (see), produced antibodies (see), there Allergy (see), local inflammatory reaction and so on
In-depending on the activator, the dose of the germ, the state of the body's resistance and other factors, the infection may end up with a disease or leak is hidden in the form of bacteria carriage CSF, parasitologically.
According to severity distinguish severe, moderate and mild forms of the disease. Sometimes there are erased form, hardly recognizable even with the application of modern methods of diagnosis.
Duration of infectious diseases is different from a few weeks (acute infection: measles, scarlet fever, typhus , and other) to several years (chronic: tuberculosis, trachoma, brucellosis and other). For some diseases after clinical recovery of the patient is observed carriage of the pathogen from 1-3 months (diphtheria and other) to several years (typhoid fever).