Contact method of infection. Mechanisms of infection transmission. Infection through the parietal route

Epidemic process - This is the process of the emergence and spread of specific infectious conditions among the population: from asymptomatic carriage to manifest diseases caused by a pathogen circulating in the community.

Epidemiology- science that:

studies the conditions and mechanisms of formation of the epidemic process,

develops anti-epidemic measures aimed at preventing and reducing infectious diseases.

The epidemic process determines the continuity of interaction between its 3 elements:

source of infection;

mechanisms, pathways and factors of transmission;

receptivity of the team.

Turning off any of these links leads to an interruption of the epidemic process.

Social environmental factors play a decisive role in the development of the epidemic process.

Let us now consider individual parts of the epidemic process.

Source of infection

Source of infectious agent - it is a living or abiotic object that is the site of natural activity of pathogenic microbes, from which infection of humans or animals occurs.

The source of infection can be:

human body (patient or carrier),

animal body (patient or carrier),

abiotic environmental objects (water, food, etc.).

Infections in which only humans serve as the source of infection are called anthroponotic .

Infections in which the source is sick animals, but humans can also get sick - zoonotic .

Infections in which environmental objects serve as the source of infection - sapronotic .

Transmission mechanism - a method of moving the causative agent of infectious and invasive diseases from an infected organism to a susceptible one.

This mechanism includes a sequential change of 3 stages:

removal of the pathogen from the host body into the environment;

presence of the pathogen in environmental objects (biotic or abiotic);

introduction of a pathogen into a susceptible organism.

The following transmission mechanisms are distinguished:

fecal-oral,

aerogenic(respiratory),

blood(transmissible),

contact

vertical(from one generation to another, i.e. from mother to fetus transplacentally)

Transmission factors - These are elements of the external environment that ensure the transfer of microbes from one organism to another.

These include water, food, soil, air, living arthropods, and environmental objects.

Transmission routes - These are specific elements of the external environment or their combination that ensure the entry of a pathogen from one organism to another under certain external conditions.

The fecal-oral transmission mechanism is characterized by:

nutritional (food),

1. contact (indirect contact) transmission routes.

The aerogenic transmission mechanism is characterized by:

airborne

airborne dust.

The transmission mechanism is characterized by:

parenteral

The contact (direct) transmission mechanism is characterized by:

1. contact-sexual (direct contact).

The vertical transmission mechanism is characterized by the transplacental route.

The Russian epidemiologist L.V. Gromashevsky formulated the law of correspondence between the transmission mechanism and the localization of the pathogen in the body.

According to this law, all infectious diseases are classified according to the mechanism and main routes of transmission as follows:

intestinal infections;

respiratory tract infections (respiratory);

vector-borne (or blood) infections;

infections of the outer integument.

In accordance with this division, each group has the following main routes of transmission:

for intestinal infections- this is alimentary, water and contact-household;

for respiratory- airborne and airborne dust;

for transmission- through vectors, parenteral and sexual;

for infections of the outer integument- wound and contact-genital transmission routes.

In addition to these basic mechanisms, for some infections, vertical transmission of infection from mother to fetus and through germ cells is possible.

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Chapter 3. Mechanisms and routes of transmission of infection

Each infectious disease has its own route of transmission of microorganisms, which was formed in the process of evolution and is the main way of preserving the pathogen as a species.

There are three phases of transition of a pathogen from one organism to another:

1) release of a microbial agent from the body into the environment;

2) presence of the pathogen in the environment;

3) penetration of infection into a completely new organism.

Transmission mechanism infection of infectious agents occurs through these three phases, but may have its own characteristics depending on the primary localization of the pathogen. For example, when a pathogen is found in the cells of the mucous membrane of the upper respiratory tract, it is released with exhaled air, which contains microbial agents in aerosols (influenza, ARVI, chicken pox, whooping cough, scarlet fever). When the infection is localized in the cells of the gastrointestinal tract, it can be released through feces and vomit (dysentery, cholera, salmonellosis).

When the pathogen is in the bloodstream, the mechanism of its transmission will be blood-sucking insects (rickettsiosis, plague, tularemia, encephalitis). Contact mechanism - due to the localization of microbes on the skin.

Depending on the primary location of the pathogen in the human body, four mechanisms of transmission of infection are distinguished:

1) airborne;

2) fecal-oral (food);

3) transmission;

4) contact and household.

Airborne(dust, inhalation) is one of the most common and fastest ways of transmitting infectious diseases. Diseases caused by both viruses and bacteria can be transmitted this way. The accompanying inflammatory process of the mucous membranes of the upper respiratory tract contributes to the spread of pathogens. A large number of microbes are released with droplets of mucus when coughing, sneezing, talking, crying, screaming. The degree of power of this depends on the characteristics (particle size is most important) of the aerosols. Large aerosols disperse over a distance of 2-3 m and quickly settle, while small aerosols cover a distance of no more than 1 m when exhaled, but can remain suspended for a long time and move over significant distances due to electric charge and Brownian motion. Human infection occurs as a result of inhalation of air containing droplets of mucus, which contain the pathogen. With this method of transmission, the maximum concentration of pathogens will be near the source of infection (patient or bacteria carrier). As you move away from the source of infection, the concentration of microbes decreases significantly, but sometimes this is enough for the development of the disease, especially if the child is weakened and the pathogen has a high degree of pathogenicity. Cases have been described in which the transmission of influenza, measles, and chickenpox viruses occurred over considerable distances, through ventilation, stairwells, and corridors. The airborne transmission route depends on the stability of pathogens in the external environment. A large number of microorganisms quickly die when aerosols dry out (influenza viruses, chickenpox, measles), while others are quite persistent and retain their vital activity and properties for a long time in the dust (up to several days). Therefore, infection of a child can occur when cleaning the room, playing with dusty toys, etc., such “dust” is effective against diphtheria, salmonellosis, tuberculosis, scarlet fever, escherichiosis and other diseases.

Fecal-oral The (food) route of transmission occurs during the transmission of intestinal infections caused by both viruses and bacteria. Transmission factors include food, dirty hands, contaminated water, flies, and various household items. More often, however, infection occurs through contaminated food products. Thus, the development of dysentery, salmonellosis, staphylococcal enterocolitis and intestinal infections caused by opportunistic microorganisms (which cause diseases under unfavorable conditions) - Proteus, Klebsiella, Pseudomonas aeruginosa - is possible. Less commonly, polio, brucellosis, foot-and-mouth disease, scarlet fever, diphtheria, yersiniosis, hepatitis A, etc. are transmitted by the fecal-oral route. Diseases can develop when humans consume meat and milk from sick animals that have not been subjected to good heat treatment (salmonellosis, foot-and-mouth disease, anthrax , tularemia), however, most often people become infected by consuming food products that contain the pathogen. Contamination of products is observed at different stages of their processing, preparation and further sale, which is often associated with violations of the technological process and sanitary standards: through the hands of food industry workers, utensils, equipment, upon contact with the contents of the gastrointestinal tract of slaughtered animals - carriers of infection, through rodents, etc.

Children become infected through milk and dairy products (cream, ice cream, sour cream, cottage cheese, cream). Milk outbreaks of morbidity are typical for children's groups, they are characterized by massiveness and a rapid increase in morbidity. Water plays an important role as a factor in the transmission of many infections: typhoid fever, hepatitis A, cholera, etc. Infection enters water through the secretions of sick people and animals, with wastewater, when sewage is washed off from the surface of the earth by rain, etc. Most pathogens retains not only its properties in the aquatic environment, but also the ability to reproduce. From the point of view of epidemiology (the study of the spread of infectious diseases), closed reservoirs pose a great danger. Water-borne epidemics are characterized by a rapid increase in morbidity among populations using water from the same body of water.

Contact and household The transmission mechanism occurs either through direct contact (direct) or through contaminated environmental objects (indirect contact). As a result of direct contact, the pathogens of diphtheria, tuberculosis, scarlet fever, herpes, scabies, helminths, and brucellosis are transmitted. With indirect contact through contaminated objects, linen, toys, dishes, the development of shigellosis, helminthiasis, typhoid fever, and in rare cases - diphtheria, tuberculosis, scarlet fever. Most often, children become infected through contaminated hands. At the same time, a sick person or a bacteria carrier can contaminate household items - dishes, toys, door handles, railings, etc. A healthy child, using contaminated objects, easily contaminates his hands and introduces the infection into his mouth.

As a transmission factor, soil is of independent importance in the transmission of anaerobic wound infections (tetanus, gas gangrene). The causative agents of these diseases enter the ground with the secretions of sick animals and people, where they form spores, maintaining their vital activity for several years.

The soil of Russia is 100% contaminated with tetanus. The development of the disease occurs when spores get on the wound surface (gas gangrene, tetanus) or in food (botulism). Soil is also important in the transmission of infectious diseases because it is a place for the vital activity of flies, rodents and the maturation of helminth eggs.

Transmissible The transmission route is carried out with the participation of a living carrier infected with the causative agent of an infectious disease.

Among the living, specific and nonspecific carriers are distinguished. Specific are blood-sucking insects (lice, fleas, mosquitoes, ticks, mosquitoes, etc.). They transmit strictly defined infections. Pathogens in the body carry out their life cycle and multiply. Humans are infected by biting or rubbing the contents of a crushed insect into damaged skin. Thus, lice transmit typhus, fleas - plague, mosquitoes - malaria, ticks - encephalitis, relapsing fever.

Mechanical (nonspecific) carriers transmit the infection in the same form in which they received it. For example, flies have pathogens of intestinal infections, hepatitis A virus, and typhoid bacilli on their legs and body. The role of mechanical transmission in the spread of diseases is relatively small.

The intrauterine (transmission) route is one in which pathogens are transmitted from the mother to the fetus through the placenta. Infection in a pregnant woman can occur either in an obvious form or as a healthy carrier of bacteria. The most relevant is the transmission of viral infections through the placenta. Transfer from mother to fetus is possible: rubella viruses, measles, cytomegaloviruses, chickenpox, hepatitis B virus, mumps, enteroviruses. Bacterial infections can also be transmitted: escherichiosis, leptospirosis, streptococcal and staphylococcal infections, protozoal diseases: toxoplasmosis, malaria, leishmaniasis. The timing of infection of a pregnant woman determines the outcome of the fetus (if a woman becomes ill in the first three months of pregnancy, then more often the fetus dies or is born with malformations (embryonopathy)). If infection occurs after three months, fetal death or birth with signs of congenital infection are also possible. Intrauterine infection is important due to its severe course, frequent mortality, and the risk of pathogen spread in the maternity hospital or prematurity unit.

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Chapter 2. Causative agent of an infectious diseaseChapter 4. Periods of infectious diseases

Review

Knowing the basic rules of hygiene, you can easily protect yourself and your loved ones from many unpleasant, dangerous and even fatal infections. Below are the main ways infections enter the body and ways to avoid them.

Airborne mechanism

The transmission of germs and viruses occurs with tiny droplets of saliva and nasal mucus, which are released by a sick person while talking, sneezing or coughing and remain in the air for some time. This is how many infections are transmitted, for example, influenza, tuberculosis, diphtheria, measles, chicken pox, meningococcal meningitis, etc.

The most dangerous airborne transmission of diseases is indoors and outdoors in spring and autumn. Winter frosts and hot summer sun, on the contrary, reduce its effectiveness.

A variation of this method is the airborne dust transmission route, when the source of infection is microbes found in dust suspended in the air. For example, tularemia, psittacosis, legionellosis, and hemorrhagic fever with renal syndrome can be transmitted.

There are several rules to protect against airborne infections:

1. Keep your distance. The further you are from a sick person, the less likely you are to “catch the infection.” Stay away from people who cough, sneeze or sniffle, even if they are your family and friends. It is advisable to isolate a sick person in a separate room. It is useful to frequently ventilate and quartz (treat with ultraviolet light) the room where a sick person is located; for this you can purchase a household UV lamp for home use. The use of aroma lamps with oils of coniferous trees, tea tree, eucalyptus or monarda can provide some help.

2. Create a barrier. To protect against flying microbes and viruses during short-term contact with a patient, in most cases, a 6-fold gauze bandage or a disposable mask, which are sold at the pharmacy, is sufficient. Remember that the same mask can only be used for two hours.

3. Lubricate your nose. To do this, you can use pharmaceutical products: oxolinic ointment, gel or Viferon ointment. These drugs have a combined effect: they strengthen local and general immunity and have an antiviral effect. If there is a high probability of becoming infected, upon returning home, wash, rinse your mouth, and also rinse your nose with warm, slightly salted water to quickly remove germs and viruses from the mucous membranes and skin.

Fecal-oral mechanism

The causative agents of the disease are excreted in the feces (feces, urine, vomit) of animals and humans and enter the soil and water. Further, if hygiene rules are not followed, germs and viruses can enter the body in different ways:

• through dirty hands - while eating (dysentery).
• food route - through contaminated foods: poorly washed fruits and vegetables (hepatitis A, botulism), eggs (for example, with salmonellosis).
• waterway - through water contaminated with feces, of poor quality, for example, with cholera.
• Participants in the fecal-oral mechanism of infection transmission often include flies and domestic cockroaches, which carry pathogens on their bodies, for example, with polio.

A surge in diseases with a fecal-oral transmission mechanism is usually observed in the summer, when the best conditions are created for the persistence of microbes in the environment and the spread of flies.

To protect yourself from unpleasant “surprises”, follow these rules:

1. Always wash your hands with soap before eating and after using the toilet. Try not to eat on the street and stop children from chewing cookies and candies while playing in the sandbox, while walking or in public transport.

2. All fruits and vegetables should be thoroughly washed before eating. Delicate fruits such as grapes, berries, ripe peaches, etc. can be rinsed in warm water with the addition of a small amount of potassium permanganate (until pink). Be especially careful when processing dried fruits and nuts that are sold without shells - they can be a source of many intestinal infections, including polio. Dried fruits can be scalded with boiling water or steamed for 5-10 minutes in the oven. It is convenient to fry the nuts in a dry frying pan.

3. When going on vacation to southern countries, do not drink raw water and homemade soft drinks offered by the local population, and do not order drinks with ice. It is advisable to use only bottled water from reputable manufacturers.

In the middle zone of our country, avoid drinking water from local reservoirs without first boiling, which often happens during picnics or hiking trips.

Contact and household path

Transmission of infections during close contact in everyday life (in the family, kindergarten group, etc.). The source of infection are household items (door and furniture handles, kitchen utensils, toys), towels and bed linen, personal hygiene products (toothbrush, comb, etc.). This is how many intestinal and respiratory infections, syphilis, etc. are transmitted.

To prevent infections that spread through contact and household routes:

1. Never use someone else’s personal hygiene items, such as a toothbrush, comb, or razor. Avoid using shared towels in cafes, canteens, and bathhouses (the same applies to slippers, flip flops, and other bath accessories).

2. When relaxing in water parks, baths, saunas, on the beach, when sitting on sunbeds, benches, chairs, shelves, place a personal towel or mat.

Sexual tract

Transmission of diseases during sexual contact (for example, sexually transmitted diseases, hepatitis C, AIDS, etc.).

As a rule, the likelihood of sexual transmission of infection depends on the health of the genital organs. Intact mucous membranes are one of the protective barriers to bacteria, viruses and pathogenic fungi. When microtraumas or inflammation appear on the skin or mucous membranes, their protective properties are sharply reduced.

Therefore, the risk of sexual infection increases with rough or intense sexual contact, with inflammatory diseases (vaginitis, urethritis, etc.), with chronic infections (candidiasis, chlamydia, etc.) and vaginal dysbiosis in women (vaginosis), as well as against the background AIDS or other immunodeficiency conditions.

To protect against sexually transmitted infections:

1. Be selective in sexual intercourse.

2. Use barrier contraception (condoms) correctly.

3. Treat genitourinary infections in a timely manner.

4. Maintain personal hygiene.

There are also methods for emergency prevention of sexually transmitted infections - these are measures that are likely to help prevent infection in the first hours after unprotected sexual intercourse:

1. You need to urinate.

2. Wash your hands thoroughly, and then thoroughly wash the genitals, perineum and inner thighs with soap (preferably laundry soap).

3. Afterwards, treat the skin of the genital organs, perineum and thighs with a cotton swab, generously moistened in a solution of antiseptics, which can be bought at the pharmacy without a prescription:

• 0.05% solution of chlorhexidine bigluconate (gibitan);
• 0.01% solution of miramistin (septic tank);
• 10% betadine solution.

4. Men are recommended to inject 1-2 ml of antiseptic solution (the above solutions of chlorhexidine or miramistin) into the urethra (opening of the urethra). After which it is advisable not to urinate for 1-2 hours.

5. Women are recommended to douche (wash the vagina) with chlorhexidine or miramistin (150-200 ml), as well as injecting 1 ml of one of these solutions into the urethra. Instead of douching, you can use vaginal suppositories: Farmotex, Hexicon, Betadine.

6. It is necessary to change contaminated underwear or, if this is not possible, isolate the genitals from it using a clean gauze napkin.

Emergency prevention significantly reduces the likelihood of contracting infections, however, for more reliable protection, it is recommended to consult a doctor in the coming days. After examination and examination, the doctor may, with your consent, prescribe postcoital prophylaxis or preventive treatment. This is taking medications against HIV and/or syphilis pathogens if there was a high risk of contracting these infections during sexual intercourse.

Parenteral mechanism

Transmission of infections through biological fluids, mainly blood, as well as saliva, genital secretions, sweat, semen, etc. Infection usually occurs during medical or cosmetic procedures, less often through close contact (kissing, shaking hands, intimate caresses, etc. ). This route of transmission is typical for scabies, herpes, hepatitis B and C, syphilis, HIV infection, etc.

Sometimes, as part of this transmission route, infection is considered during the bite of various animals, when saliva gets under the human skin (for example, with rabies).

Prevention of parenteral infections is mainly the concern of medical workers, as well as employees of beauty salons, who must properly sterilize instruments. However, there are several tips that you can follow to reduce the risk of infection:

1. Do not go to dubious establishments for manicure, pedicure, piercing and tattoo services, as well as other invasive cosmetic procedures.

2. Be careful when handling syringes and needles.

3. Avoid contact with objects contaminated with other people’s blood and other liquids; if necessary, wear gloves.

4. If an accident occurs (injection with a used needle, for example), it is necessary to consult a doctor as soon as possible for preventive (prophylactic) treatment and further observation.

5. After being bitten by a dog, cat or any wild animal, be sure to go to the emergency room, even if the wound is very small. With saliva and particles of soil, pathogens of deadly infections can enter the wound: rabies and tetanus. By introducing special serums and toxoid, it is possible to prevent the development of these diseases.

Most often, vector-borne diseases are carried by flies, mosquitoes, bedbugs and ticks, and less often by other insects. Such diseases are most common in tropical countries. As a rule, the local population suffers from a mild form of the disease, while visitors, on the contrary, experience the disease very seriously. Therefore, when going on vacation, you need to take care of prevention: necessary vaccinations, repellents, mosquito nets and curtains. Vector-borne diseases include malaria, typhus, tularemia, etc.

Wound path

With the wound route of transmission of infection, the disease develops after spores of pathogenic microbes found in the soil or on the jaws, claws, needles and other parts of animals, snakes, fish, insects, spiders, and centipedes enter the wound. This is how tetanus, gas gangrene, etc. are transmitted. Therefore, all wounds received in “field” conditions must be shown to a doctor at the emergency room so that he can carry out the necessary treatment.

Vertical path

Transmission of infection from mother to fetus during pregnancy. This route is typical for rubella, hepatitis, herpes, cytomegalovirus infection, toxoplasmosis, syphilis, etc. The likelihood of vertical transmission increases with various pathologies of the placenta - the child’s place through which the baby receives nutrition from the mother.

The only reliable way to protect against vertical transmission of diseases is their early treatment at the stage of pregnancy planning.

All site materials have been checked by doctors. However, even the most reliable article does not allow us to take into account all the features of the disease in a particular person. Therefore, the information posted on our website cannot replace a visit to the doctor, but only complements it. The articles have been prepared for informational purposes and are advisory in nature. If symptoms appear, please consult a doctor.

Mechanism of transmission of infection - a complex process that consists of three phases, following one after another: 1) removal of the pathogen from the infected organism; 2) presence of the pathogen in the external environment (or in the body of a carrier animal); 3) introduction of the pathogen into a susceptible organism.

The method of removing the pathogen from an infected body depends on its location in the body. When the pathogen is localized in the intestine, it is excreted in feces and sometimes in vomit. If the pathogen is in the respiratory system, it is released with air and droplets of saliva. In cases where the pathogen is in the human blood, it is transmitted to a healthy person mainly by blood-sucking insects.

The following main variants of the mechanism of infection transmission are distinguished: contact, airborne droplets, fecal-oral, vector-borne. These mechanisms of transmission of pathogens are carried out using specific pathways and transmission factors.

At contact mechanism transmission of infection, the pathogen is located on the skin, in the oral cavity, genitals, on the mucous membrane of the eyes, on the surface of wounds, and can enter a susceptible organism from an infected person. In this case, a distinction is made between direct contact and household contact.

Through direct contact, direct transmission of pathogens that are poorly resistant in the external environment occurs. Sexually transmitted diseases, AIDS, frequency, some fungal skin diseases and some zoonoses are transmitted this way. Through direct contact, infection with leptospirosis, foot-and-mouth disease, and tularemia can also occur.

During the contact-household route, pathogens that are stable in the external environment first land on dishes, clothes and shoes, toys and other objects, and then are introduced into the body. Basically, the transmission of pathogens occurs through human hands, which, in contact with various objects, can leave pathogenic microbes there. This route is typical for the transmission of intestinal infections.

To prevent the spread of infections through contact, various sanitary and hygienic measures are necessary, aimed at improving living and working conditions, improving sanitary culture and developing hygienic skills among the population.

Airborne mechanism contributes to the spread of many infectious diseases (influenza, measles, chickenpox, whooping cough, tuberculosis, etc.). When talking, coughing, sneezing, pathogens, along with tiny droplets of saliva and mucus, enter the air and form a so-called bacterial aerosol, which spreads very quickly with air currents. Typically, infected droplets remain in the air for 30-60 minutes, and transmission is most likely within 2-3 m from the source. The causative agents of measles, chickenpox and smallpox can also spread through ventilation ducts, leaving the premises.

Along with airborne droplets, airborne dust is also possible. Droplets of bacterial aerosol settle on surrounding objects and are then carried along with dust by the air flow. Airborne droplets contribute to the rapid spread of infection, since each infected person communicates with a large number of people during the day. Diseases spread wherever sources of infection are located. An example of such epidemics is influenza.

At fecal-oral mechanism transmission of infection, pathogens, located mainly in the intestines, enter the environment along with feces, and then enter the body through various routes through the digestive tract. Many intestinal infectious diseases are transmitted in this way: dysentery, typhoid fever, paratyphoid fever, etc. A special role here is played by the transmission of intestinal infections through water, food, and soil. In this case, typical epidemic chains are observed: feces of a patient or carrier - soil, water, food products - the body of a susceptible person.

At transmission mechanism Infectious agents are transmitted mainly by arthropods. There are mechanical (nonspecific) and biological (specific) carriers.

Typical representatives of mechanical carriers are flies. Sometimes up to 60 types of microbes are found on their paws and proboscis. Flies also excrete pathogenic microbes in their feces. Mechanical carriers are cockroaches and some blood-sucking flying insects (horseflies, burner flies). They can carry anthrax and tularemia pathogens on the surface of their piercing apparatus.

With the help of biological vectors, transmission of infection occurs as follows. From the blood or lymph of infected people or animals, pathogens enter the body of biological carriers, where they accumulate or undergo a certain development path. The pathogens then enter the susceptible organism through blood sucking or through the secretions of the carrier, penetrating through wounds on the skin. Thus, fleas cause infection with plague and rat typhus, anopheles mosquitoes - malaria, body and head lice - typhus, relapsing fever, culex mosquitoes - Japanese encephalitis, Aedes mosquitoes - yellow fever, mosquitoes - leishmaniasis, etc.

A characteristic feature of vector-transmitted infections is a clear seasonality, which is associated with the period of greatest activity of vectors. In addition, these diseases spread, as a rule, in a certain area, that is, they have a natural focality.

In addition to the common mechanisms of transmission of infections associated With Due to natural biological phenomena, human infection can also occur during various medical procedures. Pathogens can enter the body With blood transfusion when using non-sterile medical instruments (syringe, needles, etc.). Similar transmission of infection is observed in viral hepatitis, AIDS, malaria, syphilis, etc.

- Source-

Laptev, A.P. Hygiene/ A.P. Laptev [and others]. – M.: Physical culture and sport, 1990.- 368 p.

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Transmission mechanism is an evolutionarily established process of movement of a pathogen within one population from the body of one host to the susceptible organism of another host, which ensures the preservation of the pathogen as a biological species in nature.

The transmission mechanism can be divided into three interdependent (interconnected) phases (Fig. 3).

First phase- removal of the pathogen from the source of infection - is determined by the localization of the pathogen in the macroorganism and is implemented in a certain group of infectious diseases in the same way. For example, when the pathogen is localized in the intestines, there is only one way of removing it into the external environment - by defecation; when localized in the respiratory tract - there is also only one way of removing it - with the flow of exhaled air, i.e. during exhalation.

An infected human or animal organism, in which pathogenic pathogens can live, multiply, accumulate and be released into the external environment, is called a source of infection. That is, this is the natural habitat of the pathogen.

Among people, sources of infection can be patients and carriers. The most important characteristics of patients as sources of infection are the period of infectiousness and the severity of clinical manifestations of the disease.

Considering the cyclical course of infectious diseases, it should be noted that during the incubation period for most infectious diseases, pathogens are not released into the external environment and, therefore, the infectiousness of such individuals is excluded. However, if pathogens are isolated during the incubation period, this sharply increases the epidemic significance of such individuals as sources of infection and significantly complicates preventive work. This is due to the absence of clinical manifestations during the incubation period and the ability to identify such sources of infection. This situation is typical for viral hepatitis A and is one of the main reasons for the widespread spread of this infection. During the height of the disease, the number of pathogens in the patient’s body reaches a maximum. The virulence of pathogens that stand out against the background of clinical manifestations is significantly higher than in other periods of the disease. Along with this, infectious diseases are characterized by symptoms that help rid the body of pathogens (cough, runny nose - with aerosol infections; diarrhea - with intestinal infections, etc.). As a result, the peak period is characterized by the maximum release of the pathogen from the patient’s body and this determines the greatest epidemic danger of infectious patients at the height of clinical manifestations.

During the period of convalescence, in most cases, clinical recovery coincides in time with the release of the patient’s body from pathogens. Sometimes, in some individuals, against the background of clinical recovery, the release of the pathogen continues and, naturally, they can be a source of infection for others.

Thus, patients pose the greatest epidemic danger during the height of the disease. This is followed by a period of convalescence. For some infectious diseases, persons in the incubation period can also be sources of infection.

The epidemic significance of the severity of clinical manifestations is as follows. A patient with a severe form of an infectious disease, other things being equal, is a powerful source of infection, since it produces a large number of highly virulent pathogens. However, the severe course of the disease sharply limits the activity of such sources of infection, and as a result, patients with mild clinical forms pose the greatest epidemic danger. The main reasons for the high epidemic significance of patients with mild forms are: a) in the structure of morbidity, as a rule, mild forms are more common than severe ones; b) patients with mild forms seek medical help later or do not seek it at all; c) the diagnosis of such patients is established later due to the uncertainty of the clinical picture; d) isolation of patients with mild forms is less strict and is often carried out at home. The epidemic danger of patients with mild forms of infectious diseases increases even more if pathogens are isolated from the source of infection during the incubation period.

Carriage of pathogens of infectious diseases- is the isolation of a pathogen from the human body in the absence of clinical manifestations of the disease. According to duration they are distinguished transient, acute And chronic carrier status.

Transitional carriage involves a short-term (most often single) release of the pathogen in the absence of clinical manifestations of the disease.

Acute carriage - isolation of the pathogen within a period of several days to two to three months. Acute carriage is predominantly a consequence of a recent illness.

Chronic carriage- release of the pathogen for many months and even years. This type of carriage is also most often formed as a result of a previous illness in persons with defects in the immune system.

The degree of epidemic significance of these forms of carriage, other things being equal, is directly proportional to its duration. However, for certain infections in specific conditions, the role of acute carriers as sources of infection may be more significant than those in a state of chronic carrier.

When analyzing the mechanism of development of the epidemic process during zoonoses, the concepts of “main” and “additional” sources of infection are used. The main source is the specific host of the pathogen, which ensures its preservation as a biological species (natural habitat). An additional source is the nonspecific host of the pathogen, capable of transmitting it to people. In case of certain zoonoses (plague), humans can become an additional, and in epidemic terms, the most dangerous source of infection.

Reservoir of infection- a set of pathogen populations in interaction with the natural habitat.

Second phase transmission mechanism- the presence of the pathogen in the external environment depends on the method of excretion of the pathogen, which determines the environment into which it enters after removal from the macroorganism. Thus, a pathogen that leaves the body of a source of infection during a conversation, coughing or sneezing inevitably first enters the air. The pathogen released with feces ends up on various objects, which take part in its further spatial movement. Thus, the phase of the pathogen’s presence in the external environment is inextricably linked with the phase of its removal from the source of infection.

To implement the phase of residence of the pathogen in the external environment, transmission factors are necessary, i.e., elements of the external environment that ensure the movement of the pathogen from the source of infection to the susceptible organism. All elements of the external environment that act as factors for the transmission of pathogens of infectious diseases are divided into 6 groups: 1) air; 2) water; 3) food; 4) soil; 5) household items and work environment; 6) live carriers.

The elements of the external environment on which the pathogen enters when excreted from the body are called primary transmission factors, and those that deliver it to a susceptible organism are called final transmission factors. Sometimes both the primary and final transmission factors are the same element of the external environment (for example, air). In some cases, the transfer of the pathogen from the primary factor to the final factor is carried out using intermediate transmission factors.

Certain types of pathogens are evolutionarily adapted not only to a specific location in the host body, but also to specific transmission factors. These are specific factors. The rest are additional, but in certain specific conditions they can acquire important epidemiological significance.

The set of transmission factors involved in the movement of a specific pathogen from a specific source of infection to a specific susceptible organism is defined as the route of transmission of the infectious agent.

Various transmission routes are named according to the final transmission factor: airborne, waterborne, foodborne, household contact and others.

Third phase- introduction of the pathogen into a susceptible organism is determined by the previous phase (stay of the pathogen in the external environment). And the nature and nature of the factors that introduce the pathogen into a susceptible organism determine the primary localization of the pathogen in it. The pathogen is introduced into a susceptible organism through physiological (breathing, eating) and pathological (violation of the integrity of the skin and mucous membranes) processes.

Aerosol transmission mechanism- specific for pathogens of infectious diseases primarily localized in the respiratory tract (Fig. 4). In this case, pathogens are released from the source of infection in droplets (droplet phase of the aerosol), which are concentrated around the source at a distance of 1–2 m, and the risk of infection decreases in proportion to the square of the distance from the source of infection. Large drops settle quickly. The droplets remaining in the air dry out within the next 20 minutes after release. Only with the appropriate combination of temperature and humidity can they last up to two hours or more. When drying, the droplet phase of the aerosol passes into the droplet-nucleolar phase. This process is accompanied by massive death of microorganisms. Pathogens that are weakly resistant in the external environment die completely, while those that are more resistant die only partially. “Nuclei” with particles less than 100 microns in size can remain suspended for hours, move with convection currents inside the room and penetrate beyond its boundaries through corridors and ventilation ducts.

Consequently, infection by pathogens that are part of the droplet-nucleolar phase of an aerosol is possible both in the room where the source of infection is located and outside it.

Large droplets that settle on household items dry out, combine with dust, and as a result, a secondary dust phase of an aerosol containing pathogens is formed. The most important factor in the formation of the dust phase of a bacterial aerosol is sputum. Dust particles less than 100 microns in size can remain suspended for a long time, move with air currents into adjacent rooms and cause infection of susceptible individuals.

The aerosol transmission mechanism is very active, therefore, in the event of a source of infection, it ensures almost universal infection of people. Due to the simplicity of implementation of this transmission mechanism (exhalation-inhalation), and the short time spent by pathogens outside a living organism, the vast majority of them have low resistance in the external environment. The pathogens of diphtheria, measles, influenza, meningococcal infection, etc. are transmitted by the aerosol mechanism.

Fecal-oral transmission mechanism is specific for pathogens of infectious diseases, the place of primary localization of which is the gastrointestinal tract (Fig. 5).

Pathogens are released into the external environment with feces and spread mainly through three groups of transmission factors - food, water and household items. In some cases, flies (mechanical carriers) may be important in the transmission of pathogens of intestinal infections. A feature of transmission factors (food products) within the fecal-oral mechanism is that some of them serve as a favorable environment for the proliferation of pathogens. The accumulation of pathogens in such transmission factors causes infection of people with large doses of microorganisms and the development of severe clinical forms of diseases. A small number of pathogens are introduced into the human body through household items and water, so diseases associated with these transmission factors in most cases occur in mild forms. The scale of infection with infectious diseases, the pathogens of which are spread by the fecal-oral transmission mechanism, depends on the volume of consumption of contaminated food products and water. Due to the fact that the implementation of the fecal-oral transmission mechanism requires a certain time, and pathogens have to remain on transmission factors for a long period, they must have high stability in the external environment. The causative agents of typhoid fever, dysentery, and viral hepatitis are transmitted by the fecal-oral mechanism A and etc.

Transmission transmission mechanism is specific for pathogens of infectious diseases, the site of primary localization of which is the blood (Fig. 6).

Fig.6. Scheme of the transmission mechanism for transmitting the pathogen

When localized in the blood, pathogens have no exit from the body, so their further spread is only possible with the participation of blood-sucking arthropods. In the body of living carriers, either the accumulation of the pathogen or a certain cycle of its development occurs. The main carriers are mosquitoes, lice, fleas, ticks, and mosquitoes. Unlike factors of inanimate nature, living vectors actively attack people and, with significant numbers, are capable of ensuring a very high degree of their infectivity. Since pathogens transmitted by blood-sucking vectors have virtually no contact with environmental factors, they do not require high resistance, therefore most of them are characterized by weak resistance in the external environment. The pathogens of malaria, typhus and relapsing fever, etc. are transmitted by a vector-borne mechanism.

Contact transmission mechanism is specific for pathogens of infectious diseases, the place of primary localization of which is the outer integument. The contact mechanism of transmission occurs when the affected areas of the skin of the source of infection come into contact with healthy areas of the skin (mucous membranes) of susceptible people. In this case, the transmission of pathogens is carried out by direct contact. The contact mechanism of transmission also includes the delivery of the pathogen to the skin (mucous membranes) of susceptible individuals through household items contaminated with pathogens (indirect contact). The contact mechanism of transmission usually ensures limited spread of infectious diseases. In these cases, a narrow circle of people, united by household premises and using common objects, is involved in the epidemic process. The causative agents of tetanus, sexually transmitted diseases, etc. are transmitted through the contact mechanism.

Thus, the localization of the pathogen in the body of the source of infection and the mechanism of its transmission are mutually determining phenomena, which, naturally replacing each other, form a continuous chain that ensures the preservation of the pathogen as a biological species in nature.

These transmission mechanisms ensure the spread of pathogens of infectious diseases among individuals of the same generation, i.e. they are horizontal. The transmission of pathogens from mother to fetus ensures vertical (transplacental) transmission mechanism . With the vertical mechanism, transmission of pathogens occurs throughout the entire period of intrauterine development, i.e., from conception to the birth of the newborn. The most severe defects and deformities of the fetus are observed during infection at the stage of embryogenesis. Within the vertical mechanism there are 4 transmission ways: germinal (embryo), hematogenous-transplacental (hematogenous transition of pathogens from the pregnant woman to the fetus during the intrauterine period from the moment of formation of the embryo’s own blood circulation), ascending through the vagina and uterus (ingestion or aspiration by the fetus of amniotic fluid contaminated with the pathogen from the 5th month), intrapartum (infection of a newborn during its passage through the birth canal).

The epidemic significance of the vertical mechanism lies in the fact that children infected in utero from their mothers pose an epidemic danger to others. This is how the pathogens of rubella, toxoplasmosis, herpes, cytomegalovirus infections, etc. can be transmitted.

In the process of developing new methods for diagnosing, treating and preventing infectious diseases in medicine, a new mechanism for human infection by pathogens of infectious diseases has emerged. He was named artificial (artificial - artificial) (Fig. 7). The creation of large hospitals, a significant increase in the number of “aggressive” interventions, invasive diagnostic and treatment procedures, the formation of hospital strains and other factors contributed to the intensification of the artificial mechanism of infection. Within the artificial mechanism of infection, inhalation (artificial ventilation, intubation) can be implemented; contact (non-invasive therapeutic and diagnostic procedures); enteral (fibrogastroduodenoscopy, enteral nutrition); parenteral (invasive therapeutic and diagnostic procedures) transmission routes.

Rice. 7. Scheme of the artificial mechanism of infection

The artificial mechanism of infection is not a mechanism of transmission, since it does not correspond to the definition of this concept (an evolutionarily established process necessary for the existence of the pathogen as a species in nature). The causative agents of human infectious diseases, which are now more often spread through an artificial mechanism of infection (HIV, viral hepatitis B, viral hepatitis C and others), always have a natural main transmission mechanism, which determines their preservation as a species in nature.

The type of transmission mechanism can be determined only by analyzing the nature of the spread of pathogens within the population of one species. The penetration of a pathogen from a population of hosts of one species (animals) into a population of hosts of another species (humans) is not a transmission mechanism, since this movement has no significance for the preservation of the pathogen as a biological species in nature. In relation to zoonoses, the transmission mechanism occurs only during an epizootic process. In relation to people, they talk about the mechanism (process) of infection or the routes of transmission of pathogens of zoonotic infections.