Download medical textbooks, lectures. Classification of infectious diseases in connection with environmental factors Classification of infections according to L

Taking into account the above-mentioned features of the epidemic process, a modern ecological and epidemiological classification of human infectious diseases has been developed (Table 2).

Table 2.

Ecological and epidemiological classification of infectious diseases

The ecological and epidemiological division of all human infectious diseases must take into account, first of all, the habitat (reservoir) of the pathogen in nature, with which human infection is in one way or another connected.

There are 3 main specific habitats: the human body (anthroponoses), the animal body (zoonoses), and the external environment (sapronoses).

In anthroponoses, humans are the only reservoir of the pathogen in Nature and the source of infection. In this case, the classification is based on the nature of the relationship of the pathogen with the human body (localization) or with the human population (transmission mechanism).

With a more detailed classification of anthroponoses, the generally accepted division into intestinal, blood, respiratory, infections of the outer integument and vertical (from mother to fetus) infections is adhered to.

A fundamentally different picture is observed in infections whose pathogens have non-human reservoirs in nature. In these infections, the localization of the pathogen in the human body or the mechanism of its transmission from person to person is not the cause at all, but a consequence of the processes that ensure the normal functioning of the pathogenic microbe.

Zoonoses are divided into the following ecological and epidemiological groups: diseases of domestic (agricultural, fur) and synanthropic (mainly rodents) animals, as well as diseases of wild animals.

In sapronoses, the main reservoir of the pathogen is substrates external environment(soil, water, etc.), which are capable of themselves ensuring its sustainable existence in nature. For pathogens of typical sapronoses, the external environment serves as practically the only or main habitat. Other sapronoses represent a long and smooth transition to zoonotic infections, during which the role of animals as a reservoir of the pathogen gradually increases. They are called saprozoon-zami.

Classification of sapronoses by transmission mechanism is impossible. Humans and warm-blooded animals are a biological dead end for the pathogen, therefore there is no natural chain transmission from individual to individual. The epidemic process has a qualitatively different - fan-shaped - character: independent infections of people from a common reservoir - substrates of the external environment. From an epidemiological point of view, sapronoses are divided according to natural reservoirs into soil and water.

“Pure” sapronoses - natural focal diseases. Their pathogens are components of natural terrestrial or aquatic ecosystems. The autonomous existence of Legionella in natural reservoirs, clostridia and fungi that cause deep mycoses in the soil has been proven.

The causative agents of infectious diseases, as we saw above, are transmitted from patients to healthy people in various ways, i.e., each infection is characterized by a specific transmission mechanism. The mechanism of transmission of infection was put by L.V. Gromashevsky as the basis for the classification of infectious diseases. According to the classification of L. V. Gromashevsky infectious diseases are divided into four groups.

I. Intestinal infections. The main source of infection is a sick person or a bacteria carrier who excretes huge quantities pathogens. With some intestinal infectious diseases, it is also possible to isolate the pathogen in vomit (cholera) or in urine ( typhoid fever).

The infectious agent enters the body through the mouth along with food or drinking water, contaminated in the external environment in one way or another. The mechanism of transmission of the infectious principle during intestinal infections is schematically presented in Fig. 1.

Intestinal infectious diseases include typhoid fever, paratyphoid A and B, dysentery, amoebiasis, toxic infections, cholera, Botkin's disease, polio, etc.

II. Infections respiratory tract. The source of infection is a sick person or a bacteria carrier. Inflammatory process on the mucous membranes of the upper respiratory tract causes coughing and sneezing, which causes a massive release of the infectious principle with droplets of mucus into the surrounding air. The pathogen enters the body healthy person when inhaling air containing infected droplets (Fig. 2). Respiratory tract infections include influenza, Infectious mononucleosis, smallpox, epidemic meningitis and most childhood infections.

III. Blood infections. The causative agents of this group of diseases are mainly localized in the blood and lymph. Infection from the blood of a patient can enter the blood of a healthy person only with the help of blood-sucking carriers (Fig. 3). A person with an infection of this group is practically not dangerous to others in the absence of a carrier. The exception is the plague ( pulmonary form), highly contagious to others.

The group of blood infections includes eruptive and relapsing fever, tick-borne rickettsiosis, seasonal encephalitis, malaria, leishmaniasis and other diseases.

IV. Infections of the external integument. The infectious principle usually penetrates through damaged outer skin. These include venereal diseases sexually transmitted diseases; rabies and sodoku, infection of which occurs when bitten by sick animals; tetanus, the causative agent of which enters the body through a wound; anthrax, transmitted by direct contact from animals or through household items contaminated with spores; glanders and foot-and-mouth disease, in which infection occurs through mucous membranes, etc.

It should be noted that with some diseases (plague, tularemia, anthrax, etc.) there may be a multiple mechanism of transmission of infection.

The classification of infectious diseases determines general ideas about directions and measures to combat them. There are quite a few classifications based on different principles.

Etiological classification of infections

Helminthiasis And infestations It is a stretch to classify them as infectious diseases. But, historically, the situation has developed that the responsibility for diagnosing helminthiasis and deworming is assigned to the infectious disease service (partially to the local outpatient network). Infestations are the area of ​​competence of dermatologists.

Ecological classification of infections

This classification is especially important from a practical point of view for planning and implementing anti-epidemic measures. The classification is based on the principle of the pathogen’s habitat, without which it cannot exist as a biological species.

According to the ecological classification, all infections can be divided into three groups:

1. Anthroponoses- the habitat of the pathogen is the human body: acute respiratory infections, typhoid fever, measles, diphtheria...
2. Zoonoses- the habitat of the pathogen is an animal organism: salmonellosis, rabies, tick-borne encephalitis…
3. Sapronoses- the habitat of the pathogen is the external environment (soil, water bodies, plants): cholera, clostridiosis...

Within the framework of sapronoses, it is customary to distinguish saprozoonoses(zoophilic sapronoses) - infections whose pathogens have two habitats (animal organism and the external environment), and the periodic change of these habitats ensures the normal functioning of these pathogens as biological species: anthrax, pseudomonas infection, leptospirosis, yersiniosis, pseudotuberculosis, listeriosis...

Classification of infections according to L. V. Gromashevsky

The criteria for classification according to Gromashevsky are the mechanism of transmission of the pathogen and its localization in the host body:

1. Fecal-oral mechanism of infection transmission - intestinal infections.
2. Aerosol mechanism of infection transmission - respiratory tract infections(respiratory infections).
3. Transmissible mechanism of infection transmission using arthropod vectors - vector-borne (blood) infections.
4. Contact mechanism of infection transmission - infections of the outer integument(skin infections).

It should be said that the Gromashevsky classification is ideal for anthroponoses, but not entirely suitable for zoonoses and saproponoses. Zoonoses are characterized by several transmission mechanisms (sometimes Main way transmissions cannot always be established). The localization of zoonotic pathogens may be multiple, and saproponoses may not have a regular mechanism of pathogen transmission at all.

At this time, there is the most acceptable ecological and epidemiological classification for zoonoses for clinicians:

1. Diseases of domestic and synanthropic (rodents) animals.
2. Diseases of wild animals (natural focal ones).

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In the 19th century, infectious diseases were divided into contagious (transmitted from person to person), miasmatic (transmitted through the air) and contagious-miasmatic. IN late XIX century, in connection with the development of bacteriology, classifications appeared, which were based on etiological sign. These classifications could not satisfy clinicians and epidemiologists, since diseases with diverse pathogenesis were combined into one group. clinical course and various epidemiological patterns. Classifications based on clinical and epidemiological characteristics also turned out to be irrational.
The most consistent and consistent classification is that proposed by L.V. Gromashevsky. It is based on a single feature - the localization of the pathogen in the body. In accordance with this main feature, which determines the mechanism of transmission of infection, all infectious diseases are divided by the author into four groups: 1) intestinal infections; 2) respiratory tract infections; 3) blood infections; 4) infections of the external integument. Due to the fact that the epidemiology and prevention of anthroponoses and zoonoses differ significantly, it is proposed that each group in the classification of L.V. Gromashevsky be divided into two subgroups - anthroponoses and zoonoses.

Intestinal infections.

Intestinal infections are characterized by the localization of pathogens in the intestines and, accordingly, their release into the external environment, mainly with feces. For those diseases that are accompanied by the circulation of the pathogen in the blood (typhoid fever, paratyphoid fevers A and B, leptospirosis, ornithosis, viral hepatitis, brucellosis, etc.) additional ways of excreting it through organs (liver, kidneys, lungs, mammary glands, etc.) are possible.
Pathogens of intestinal infections, entering the external environment with feces, urine, vomit of a patient (cholera), can cause illness in a healthy person only if they entered his body through the mouth along with food or drinking water or were brought in with dirty hands (Fig. 2). In other words, intestinal infections are characterized by a fecal-oral transmission mechanism.
Rise in incidence intestinal infections observed in the warm season - summer and summer-autumn.
Intestinal infections from the subgroup of anthroponoses include typhoid fever, paratyphoid fever, bacterial and amoebic dysentery, cholera, infectious hepatitis, poliomyelitis, helminthiases (without a second host), to the subgroup of zoonoses - brucellosis, leptospirosis, salmonellosis, psittacosis, botulism, etc.
The main ways to combat intestinal infections are sanitary and health measures that eliminate the possibility of transmission of pathogenic pathogens through food products, water, flies, dirty hands, etc. Great importance have also timely detection and isolation of patients and carriers, removal from work of carriers working in food and similar enterprises.
Specific immunization for intestinal infections plays a supporting role.

Rice. 2. Scheme of the mechanism of transmission of pathogens during intestinal infections (Gromashevsky L.V.).
I - infected organism; II - healthy body; 1- isolation of the pathogen; 2 - presence of the pathogen in the external environment; 3 - introduction of the pathogen into the body.

Respiratory tract infections.

Blood infections such as tick-borne encephalitis, Japanese encephalitis, pappataci fever, and malaria are characterized by natural focality, which is determined by the presence of geographic, climatic, soil and other conditions for the existence of infection carriers. The rise in incidence of these diseases occurs during the warm season, which coincides with the maximum activity of infection carriers - ticks, mosquitoes, mosquitoes, etc.
Measures to combat typhus are aimed at neutralizing the source of infection - a sick person, eliminating lice infestations among the population and, first of all, at the source of infection.
The fight against other blood infections consists of changing natural conditions, carrying out irrigation and drainage work to drain swamps, destroying breeding sites of infection vectors, replacing adobe buildings with comfortable premises, landscaping and economic development of the area, etc., carrying out disinfestation measures to destroy mosquitoes, mosquitoes, ticks, etc., neutralizing sources of infection by isolating them and treating them, carrying out preventive treatment.
In cases where the source of infection is rodents, deratization measures are carried out.
To prevent some diseases of this group, active immunization is used.

Infections of the external integument.

Infection with infections of the external integument occurs when pathogenic pathogens come into contact with the skin or mucous membranes of a healthy person (Fig. 5). In some infections (tetanus, dermatomycosis), the pathogen is localized at the entrance gate, in others (erysipelas, foot and mouth disease, anthrax, etc.) it affects skin, penetrates the body and enters various organs and tissues through the bloodstream. Most often, in case of infections of the external integument, the factors of transmission of pathogens are bedding, clothing, dishes, water, etc., contaminated with mucus, pus and scales. The causative agents of sexually transmitted diseases, rabies, and sodoku are transmitted without the participation of the external environment. For wound infections characterized by a violation of the integrity of the outer integument as a result of injury (tetanus, erysipelas).
The main measures to combat infections of the external integument are isolation and treatment of the source of infection, destruction stray dogs, cats, identification and destruction of sick animals, improving the sanitary culture of the population, improving everyday life, observing the rules of personal hygiene, combating injuries, specific prevention.

For the first time, a consistently consistent classification of infectious diseases based on a single characteristic (localization of the pathogen in the body) was proposed by L. V. Gromashevsky. In accordance with the main localization of the pathogen in the body, which determines the mechanism of transmission of infection, all infectious diseases are divided into 4 groups:

1) intestinal infections

2) respiratory tract infections

3) blood infections

4) infections of the external integument

Within these groups, subgroups are distinguished in accordance with this principle.

Due to according to epidemiological characteristics infectious diseases of anthroponotic and zoonotic nature have significant differences, the team of the Department of Epidemiology of the Order of Lenin Central Institute improvement of doctors, the USSR Ministry of Health proposed dividing each group in Gromashevsky’s classification into two subgroups: anthroponoses and zoonoses.

Intestinal infections. Intestinal infections are characterized by the localization of the pathogen in the intestine (intestinal contents, thickness of the mucous membrane, submucosal tissue, lymphatic formations). Causative agents of many diseases: cholera, bacillary dysentery, some helminthic infestations etc., do not penetrate beyond the intestines or into other organs and tissues. In contrast, the causative agents of a number of diseases (amoebiasis, ascariasis, trichinosis, echinococcosis, etc.) in the course of evolution have developed the ability to temporarily or permanently leave the intestine. In a number of diseases (typhoid fever, paratyphoid A and B), the pathogen, multiplying in the intestines, penetrates the blood and internal organs.

Fecal-oral transmission mechanism, characteristic of intestinal infections, is characterized by a number of features. The pathogen enters the external environment from the body with the contents of the intestine and much less often through other routes. Therefore, there is a possibility for it to get directly or indirectly (carried by flies, dirty hands, etc.) into any object located in a person’s environment (water, food products, household items and furnishings, etc.). The pathogen is introduced into the human intestine through the listed transmission factors only through the mouth.

Intestinal infections, with the exception of helminthiasis, do not tend to cover the entire population. Even with a very high incidence in the area, many usually do not get sick. Therefore, complete natural immunization is virtually impossible. It is clear from this that the incidence of intestinal infections, unlike respiratory tract infections (influenza, measles, etc.), is regulated not by immunity, but by the infectiousness of the population.

Rise in incidence intestinal infections coincides with the warm period of the year. Depending on the climatic and geographical features of the area, the largest number of diseases is usually recorded in the summer and summer-autumn.

Respiratory tract infections. The pathogens of this group are localized in the mucous membrane of the respiratory tract. In a number of diseases, while maintaining their primary localization, they penetrate through the bloodstream or other routes into various organs and tissues. The pathogen is released from the body with a stream of air, especially during talking, coughing 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 time remain suspended in the air or settle on various objects in the human environment, where they dry out. When dried, already in the form of dust, the contents of the droplets often re-enter the air.

Thus, the pathogen enters the next (susceptible) organism with inhaled air in the contents of droplets (droplet infection) or, less commonly, with dust particles (dust infection). It is clear that dust infection is possible with diseases whose pathogens are able to resist drying (tuberculosis, diphtheria, etc.).

Other routes of infection are much less likely. It was mentioned above that the causative agents of some infections, along with the primary one, also have a secondary localization in the body. Due to its pathogens, smallpox, alastrima, chickenpox, leprosy, localized in the skin and mucous membranes (pustules, granulomas), and with leprosy in other organs and tissues, can enter another organism through various objects. Transmission of infection through various objects is especially characteristic of diphtheria, mumps, scarlet fever and tonsillitis of various etiologies. In this case, items that are exposed to saliva during use (dishes, drinking fountains, whistles, mouthpieces, etc.) are of paramount importance.

Transmission mechanism Respiratory tract infections (droplet or dust) occur extremely easily. Infection mostly occurs through fleeting contact between the patient and susceptible people.

Respiratory tract infections are very widespread. Many of them are difficult to avoid, and people get sick with some infections many times during their lives.

An important epidemiological feature number of respiratory tract infections is the high incidence of children in the first years of life. It is no coincidence that many diseases from this group have long been given the name childhood infections. Some researchers are still inclined to explain this pattern by the higher susceptibility of children compared to adults. In fact, the sharp difference in incidence is explained by the presence of immunity in adults acquired as a result of illness in childhood.

For this group of infections characterized by cyclical rises and falls in morbidity over a number of adjacent years and within a year.

Blood infections. Pathogens in the body are localized in the bloodstream, lymphatic system and sometimes in various organs. The main feature in localization is, therefore, that the pathogen is located in the body in a closed system. Its exit beyond the boundaries of the infected organism and introduction into another susceptible organism is practically possible only with the participation of blood-sucking arthropods.

It is also necessary to take into account in the conditions of epidemiological practice such random possibilities as blood transfusion, transfer during medical manipulations, accompanied by a violation of the integrity blood vessels, injury during autopsy of infected corpses, infection during skinning of rodents, etc.

Transmission mechanism Blood infections with an abundance of arthropods may be more active than the droplet transmission mechanism characteristic of respiratory tract infections.

For most blood infections characteristic strict confinement to a specific territory. The endemicity of a number of diseases does not extend beyond the distribution of their carriers (malaria, yellow fever, etc.), but it is not characteristic only of infections transmitted by lice.

Important feature Blood infections associated with the characteristics of the biology of vectors should also be considered their inherent seasonality. Fresh infections and an increase in morbidity, with a few exceptions (typhoid and relapsing fever), are observed in the warm season and coincide with the maximum activity of arthropods.

Infections of the external integument. The causative agents of typical infections of the external integument (trachoma, ringworm, scabies, etc.) in the body are localized in the skin and its derivatives and in visible mucous membranes. At the same time, pathogens of a number of diseases, affecting the outer integument, penetrate more or less deeply into the underlying tissues (tetanus, erysipelas, gas gangrene, cutaneous form anthrax etc.) or spread into deeper tissues and organs, from where they are excreted from the body (glanders, foot and mouth disease, actinomycosis, hookworm disease, etc.). Pathogens of rabies and sodoku from the place of introduction (wound) reach salivary glands. Finally, the causative agents of sexually transmitted diseases are localized in the mucous membrane of the genital organs and penetrate other tissues.

Due to the peculiarities of the localization of pathogens in the body, the mechanism of transmission of infections of the outer integument is very diverse. The transmission of pathogens of most diseases occurs through various objects that a person uses in the process of life, contaminated with mucus, pus, scabs, scales, etc. The pathogens of sexually transmitted diseases and especially diseases associated with a bite (rabies, sodoku) are transmitted without the participation of the external environment . Syphilitic and gonorrheal infections can be transmitted through hands, towels, dishes, tools, water, etc.

Epidemiologically diseases of the outer integument are very different. The spread of many diseases in this group is influenced by the level of sanitary culture and the quality of treatment and preventive services for the population. The epidemiology of wound infections is fully determined by the nature of the injury (agricultural, household, military). The spread of a number of diseases is also influenced by the epizootic situation. The seasonality of infections of the external integument is also varied.