Intestinal infections are characterized by the localization of the pathogen in the intestine (intestinal contents, mucosa thickness, susling tissue, lymphatic formations).
The pathogens of many diseases: cholera, bacterial dysentery, some worm infestations, etc., outside the intestines, in other organs and tissues do not penetrate. In contrast, the pathogens of a number of diseases (amebiasis, ascaridosis, trichinelles, echinococcosis, etc.) during evolution have developed the ability to temporarily or permanently go beyond the intestines. In a number of diseases (typhoid fever, paratyphoids A and B) the pathogen, multiplying in the intestine, penetrates the blood and internal organs.
The fecal-oral mechanism of transmission, characteristic of intestinal infections, is characterized by a number of traits. The pathogen enters the external environment from the body with the contents of the intestines and much less frequently other ways.
Therefore, it is possible to get it directly or indirectly (skid flies, dirty hands, etc.) into any object surrounded by a person (water, food, household items and furnishings, etc.). In the intestines of the person through these factors of transmission the pathogen is brought only through the mouth.
Intestinal infections, with the exception of helminthses, do not tend to reach the population. Even with very high incidence in the area, many people usually do not get sick. Therefore, continuous natural immunization is virtually impossible. It is clear from this that the incidence of intestinal infections, unlike respiratory infections (influenza, measles, etc.) is regulated not by immunity, but by the infection of the population.
The rise in intestinal infections coincides with the warm period of the year. Depending on the climatogeographic characteristics of the area, the highest number of diseases is usually recorded in summer and summer-autumn.
The pathogens of this group are localized in the mucous membrane of the airways. In a number of diseases, while maintaining primary localization, they with the current of blood or other means penetrate into various organs and tissues.
From the body the pathogen is released with a jet of air, especially during conversation, cough and sneezing. Droplets of mucus, exudate, particles of dead epithelium, containing the pathogen, depending on the size and influence of other factors more or less long remain suspended in the air or settle on various objects in the environment of the person, where they dry up. In a dried-up state, already in the form of dust the contents of droplets often re-enter the air.
Thus, the next (receptive) organism pathogen gets with inhaled air in the contents of droplets (drop infection) or, less often, with particles of dust (dust infection). It is clear that dust infection is possible in diseases, the pathogens of which are able to resist drying (tuberculosis, diphtheria, etc.).
Other ways of infection are much less likely. The pathogens of some infections, along with the primary, have secondary localization in the body. Due to its pathogens smallpox, chickenpox, leprosy, localizing in the skin and mucous membranes (pustules, granulomas), and leprosy and other organs and tissues, through various objects can get into another organism. The transfer of infection through various objects is especially typical for diphtheria, mumps, scarlet fever and sore throats of various etiology. In this case, the most important are the items on which saliva (dishes, drinking fountains, whistles, mouthpieces, etc.) are paramount.
The mechanism of transmission of respiratory tract infections (drop or dust) is extremely easy. Infection mostly occurs when the patient and susceptible people communicate with fleeting communication.
Respiratory infections are very common. Many of them are hard to avoid, and some infections people get sick during life many times.
An important epidemiological feature of a number of respiratory tract infections is their high coverage of children in the first years of life. It is no coincidence that many diseases in this group have long been given the name of childhood infections. Some researchers still tend to explain this pattern to a higher susceptibility of children than adults. In fact, the sharp difference in morbidity is due to the presence of immunity in adults acquired in childhood.
This group of infections is characterized by cyclical ups and downs over a number of related years and within a year.
The pathogens in the body are localized in the circulatory, lymphatic system and sometimes in various organs. The main feature in localization is, therefore, that the pathogen is in the body in a closed system. Its exit beyond the infected organism and introduction into the next susceptible organism is practically possible with the participation of blood-sucking arthropods.
It is also necessary to be considered in the conditions of epidemiological practice with such random possibilities as blood transfusion, transfer during medical manipulations, accompanied by violation of intact blood vessels, wounding during the autopsy of infected corpses, infection when removing skins from rodents, etc.
The mechanism of transmission of blood infections in the abundance of arthropods in its activity can exceed the drip mechanism of transmission, characteristic of respiratory infections.
For most blood infections, there is a strict timed to a certain area. The endemicity of a number of diseases does not extend beyond the spread of their vectors (malaria, yellow fever, etc.), but it is not unique to lice-transmitted infections.
An important feature of blood infections associated with the peculiarities of vector biology should be considered and inherent seasonality. Fresh infections and an increase in morbidity, with a few exceptions (snr and recurrent typhoid), are observed in the warm season and coincide with the maximum activity of arthropods.