What are the routes of transmission of infection? Routes of transmission of infection (artificial, vector-borne, parenteral, airborne, contact, fecal-oral). Transmission routes inherent in the blood-contact mechanism

• bacteria (cause plague, leprosy, syphilis, tuberculosis, cholera, diphtheria, and, according to recent discoveries, even cancer);
• viruses (ARVI, herpes, influenza, AIDS);
• mushrooms (diseases of the skin, respiratory system, intoxication);
• protozoa (dysentery, malaria, balantidiasis);
• prions (cause fatal diseases of the brain and nervous system);
• helminths;
• insects (lice, bedbugs, ticks).

Types of infectious diseases and mechanisms of their transmission

1. Intestinal (salmonellosis, dysentery, cholera).
2. Blood (HIV, malaria).
3. Skin (tetanus).
4. Respiratory tract (flu, chickenpox, whooping cough, ARVI).
5. Infections with several modes of transmission (enterovirus and others).

The mechanisms of transmission of all known infections are divided into 2 types: natural and artificial.

The following mechanisms of infection are considered natural:

• aerogenic;
• contact;
• transmissible;
• fecal-oral, or nutritional;
• blood-contact.

The artificial type includes a single infection mechanism:

• artificial.

Let's look at them in more detail.

Aerogenic

This mechanism of infection transmission is that microbes are transferred from sick to healthy people through the air and mainly affect the organs of the respiratory system, less often the oral cavity. At the same time, the most common illnesses that can be contracted are influenza, acute respiratory infections, tuberculosis, measles, whooping cough, chickenpox, diphtheria, bronchitis, tonsillitis, and herpes.

There are two ways of aerogenic transmission of microbes:

1. Airborne. This is the most widespread and most virulent path. It lies in the fact that microbes (usually viruses, but can also be bacteria) fly out of the mouth and nose of an infected person into the environment when coughing and/or sneezing, and from there they inhale into the body of a healthy person.
2. Airborne dust. This path is similar to airborne droplets. The difference is that the germs that come out of a sick person with coughing and sneezing settle on dust particles, and with them, when inhaled, enter a new victim. This route of infection allows microbes to survive longer in the external environment.

Contact

This mechanism of transmission of infection occurs through damage to the tissues of the skin or mucous membranes of a person, when there is direct contact (for example, touching) with the skin, mucous membranes of an infected person, or when using household items contaminated with microbes.

There are two types of contacts that lead to infection:

1. Straight. There are three transmission routes:

• sexual;
• non-sexual (for example, shaking hands);
• contact with sick animals (bite, touching affected fur, etc.).

2. Indirect. The routes of infection are as follows:

• through the soil (tetanus is transmitted);
• through dishes, clothes, toys, any household items that contain pathogenic microbes.

Microorganisms that use the contact mechanism of infection are highly resistant and are able to remain virulent in the external environment for many months.

The list of diseases that can be contracted through contact is quite impressive. These are all mycoses, lichen, scabies, lice, all sexually transmitted diseases, AIDS, hepatitis B, glanders, rabies, sodoku, stomatitis and others.

Transmissible

This mechanism of infection transmission is based on the fact that pathogenic microbes found in the blood and/or lymph of a sick person move into the body of a new victim using insect vectors.

There are two ways of transmitting infection:

• a bite of an insect;
• cutting up a sick animal.

Diseases that can be transmitted are malaria, tularemia, encephalitis, typhus, Chagas disease, yellow fever, relapsing fever. The infection is carried by mosquitoes, ticks, bedbugs, tsetse flies, fleas and other blood-sucking insects.

Fecal-oral, or nutritional

The fecal-oral mechanism of transmission of infection is a method of infection based on the fact that microbes living in the gastrointestinal tract of a sick person are released into the environment with feces (less often with urine or vomit), and then re-infect their victim or a healthy person, entering his oral cavity.

Since microbes cannot immediately implement their insidious plan with this infection mechanism, they have developed several tricks in the course of evolution that help them, firstly, to safely survive the period of waiting for the victim, and secondly, to speed up the process of penetration into a new host. What kind of tricks are these?

The mechanism of transmission of intestinal infections is possible if the following routes of infection occur:

As we can see, all intestinal infections penetrate their victims through the mouth if cleanliness and hygiene are not observed.

Hemocontact

This mechanism of infection transmission occurs when the blood of a healthy person comes into contact with the blood or lymph of an infected person. We will consider the routes of infection below.

Transplacental or vertical

Consists of infection by a pregnant woman of the fetus in her womb. This route is possible for those microorganisms that are able to penetrate the placental barrier.

To a lesser extent, the vertical mechanism of infection of infants occurs during childbirth.

Transplacental infections are extremely dangerous for the fetus, as they can cause its death or the appearance of various developmental defects. The main diseases are toxoplasmosis, intrauterine herpes, cytomegaly, listeriosis, congenital pneumonia, intrauterine sepsis.

When passing through the birth canal, the baby can become infected with fungal diseases (candidiasis), sexually transmitted diseases and HIV.

Medical manipulations

These include injections, blood transfusions, and any activities in which the blood of a sick person infected with pathogens enters the blood of a healthy person.

Many microorganisms use different ways to penetrate a new victim. A typical example is HIV infection. The mechanism of transmission here is mainly contact, and the route of transmission is sexual, when partners have sex without condoms. In addition, HIV infection is possible vertically (infants become infected at the birth stage), through medical procedures (injections, organ transplants, blood transfusions), through breast milk, through a kiss, if there are wounds in the mouth or lips.

Artificial

This is the only artificial mechanism of infection transmission based on the use of unsanitized instruments and other medical equipment by healthcare workers. Microorganisms did not invent this mechanism of infection; it was “introduced” by unscrupulous medical workers. Almost any disease is transmitted through the artificial method, depending on the treatment profile of the medical institution. The possible transmission routes are as follows:

• manipulations by doctors and nurses using instruments (operations, injections, dressings, etc.);
• diagnostics (punctures, gastroscopy, bronchoscopy, colonoscopy);
• administration of drugs enterally or intravenously;
• household route of transmission (if proper sanitation and cleanliness in hospitals is not observed).

The emergence of an infectious disease and the development of an epidemic is possible when there are 3 factors:

1. Source of infection (contamination).
2. Mechanism of transmission of infection.
3. Susceptible organism (human).

1. Sources of infection are infected people and animals - these are the natural hosts of pathogens of infectious diseases, from which pathogenic microorganisms are transmitted to healthy people.

In cases where the source of the pathogen is an infected person, we speak of anthropogenic infectious diseases or anthroponoses.
In cases where the source of infection is various animals and birds, we speak of zoonotic infections or zoonoses.

2. Under the transmission mechanism pathogenic microbes is understood as a set of evolutionarily established methods that ensure the movement of a living pathogen from an infected organism to a healthy one. This process consists of three phases:

The pathogen, released from the body of a patient or carrier, enters a healthy body after some movement in space. Objects of the external environment, including living carriers, with the help of which the pathogen moves in space from the source of infection to a healthy body are called transmission factors or ways of spreading infection.

Routes of transmission of infections are grouped into the following groups:

1. fecal-oral transmission - the pathogen is excreted from the patient’s body in feces, infection occurs through the mouth with contaminated food or water;
2. aerogenic transmission route (transmission through the air) – the causative agent of the disease is released when the patient breathes, talks, coughs, sneezes, infection occurs through the upper respiratory tract with droplets of mucus or dust particles;
3. contact transmission path – the pathogen is transmitted through the outer skin by direct contact (direct contact) or through external objects;
4. transmission path - transmission of pathogens by insects: lice, fleas, ticks, mosquitoes, flies, etc., while insects can be mechanical carriers of microbes or transmit the pathogen to humans through bites.

3.Susceptibility of the body – the biological property of the tissues of a human or animal body to be an optimal environment for the propagation of a disease pathogen and to respond to the introduction of the pathogen by an infectious process in various forms of its manifestation.

The activity of the epidemic process changes under the influence of natural and social conditions. The influence of social conditions on the course of the epidemic process is more significant compared to the influence of natural conditions.

Social conditions mean: population density, housing conditions, sanitary and communal improvement of populated areas, material well-being, working conditions, cultural level of people, migration processes, health care conditions, etc.

Natural conditions include climate, landscape, flora and fauna, the presence of natural foci of infectious diseases, natural disasters, etc.

Missing one of the three factors makes it impossible for infectious diseases to spread. Only in some diseases, such as rabies, syphilis, gonorrhea, AIDS, etc., transmission of microbes occurs through direct contact, i.e. during a bite, during sexual intercourse, etc., where two factors are involved - the source of infection and the susceptible organism.

HIV is transmitted through sexual intercourse, parenteral blood injection, and vertically from mother to child.

The main route of infection in children is vertical transmission of HIV, which is responsible for almost all new cases. The incidence of vertical mother-to-child transmission varies among countries. According to the largest studies, the rate of HIV transmission among untreated women is 12-30%. In Haiti and Africa this figure is higher (25-52%).

The incidence of HIV transmission decreases sharply when the mother is treated perinatally with antiretroviral drugs.

Vertical transmission of HIV is possible before birth (intrauterine infection), during childbirth, and after it (during breastfeeding). Intrauterine infection is indicated by the detection of HIV by culture or PCR in fetal tissues, starting from 10 weeks. pregnancy. In addition, in the first trimester, placental tissue in HIV-infected women contains HIV, which has been proven by in situ hybridization and immunohistochemical methods. It is generally accepted that 30-40% of infected newborns become infected in utero, as this percentage represents laboratory evidence of infection (positive culture or PCR) in the first week of life. Some studies have found that detection of the virus soon after birth also correlates with early onset of symptoms and rapid progression, consistent with prolonged exposure to infection during pregnancy.

Most HIV-infected children acquired the virus at birth, as evidenced by the fact that in 60-70% of infected newborns the virus was not detected until the end of the first week of life. The mechanism of transmission of the virus involves infected blood, cervical and vaginal secretions located in the birth canal; in these fluids at the end of pregnancy and during childbirth, high titers of HIV are detected. Moreover, an international registry of HIV-infected twins found that the risk of infection for the twin born first was three times higher due to a longer stay in the birth canal.

The rarest type of vertical transmission in industrialized countries is breastfeeding; in contrast, in developing countries, breastfeeding plays a significant role in vertical transmission of HIV. In HIV-infected mothers, both free and cell-associated virus have been detected in breast milk. A meta-analysis of prospective studies found that the risk of vertical transmission of HIV during breastfeeding was 14% for mothers infected before pregnancy and 29% for mothers infected after delivery. These data indicate that viremia, which accompanies primary HIV infection in the mother, doubles the risk of transmission of the virus to children. Therefore, if a mother knows that she is HIV positive or is at risk of contracting HIV, it seems reasonable to switch to formula feeding. However, in developing countries, it is recommended that HIV-infected mothers continue to breastfeed, since a significant proportion of infant mortality in these countries is due to other diseases (diarrhea, pneumonia, malnutrition) and the risk of vertical transmission of HIV is outweighed by the benefits of breastfeeding.

Several factors increase the risk of vertical transmission of the virus: premature birth (before 34 weeks of pregnancy), low CD4 cell counts in the mother before birth, and drug use during pregnancy. Of greatest importance is an anhydrous interval of more than 4 hours and a birth weight of less than 2500 g - any of these factors doubles the frequency of vertical transmission of HIV. A meta-analysis of more than 1,000 pregnancies found that elective caesarean section combined with maternal and infant zidovudine reduced HIV transmission by 87%. However, because these data were obtained before the introduction of highly active antiretroviral therapy, the beneficial effect of cesarean section appears to be insignificant if the maternal viral RNA concentration is less than 500 copies per ml. Although a number of studies have documented increased rates of infection in women with advanced infection (i.e., AIDS) or high concentrations of viral RNA (>50,000 copies/mL), some women who transmitted HIV to their children had no symptoms or concentrations of viral RNA. viral RNA was low (but detectable).

One mechanism can be realized in different ways, for example: the fecal-oral mechanism corresponds to the contact-household, food and water routes; aerosol-aerogenic - airborne droplets and airborne dust; hemocontact - parenteral, transplantation, vertical and sexual.

1. The fecal-oral mechanism occurs through direct contact (direct contact) or through contaminated environmental objects (indirect contact).

Contact and household path - through household items (towel, linen, toys, dishes); often performed for shigellosis.

Food route - through milk and dairy products, meat, eggs, fish, contaminated vegetables, fruits, etc.; is essential for shigellosis, salmonellosis, and intestinal infections.

Waterway: typhoid and paratyphoid fever, shigellosis (Flexner's Shigella), tularemia, leptospirosis, viral hepatitis 4 (VP4), cholera. 2.

Aerosol-aerogenic mechanism

Airborne transmission - the penetration with air of droplets of infected mucus and saliva released when coughing, sneezing and talking; measles, chicken pox, influenza, etc. are transmitted in this way.

Airborne dust path - particles of suspended dust containing an infectious agent enter the human body with air (for diphtheria, scarlet fever, etc.). 3.

The transmission mechanism is carried out through carriers, which are most often the biological hosts of pathogens and less often - mechanical carriers. Carriers are divided into two groups: 1)

specific fleas - plague, lice - typhus, mosquitoes - malaria, mosquitoes - pappataci fever, leishmaniasis, ticks - arboviral encephalitis, relapsing fever, etc.; 2)

nonspecific (flies - acute intestinal infections, hepatitis L, typhoid fever and paratyphoid fever). 4.

Hemocontact mechanism

Vertical (transplacental, intrauterine) route - transmission of the pathogen through the placenta (vertically) from mother to fetus; the possibility of transmission of rubella, measles, chickenpox, mumps, hepatitis B, cytomegalovirus (CMV), enteroviruses, human immunodeficiency virus (HIV), pathogens of listeriosis, leptospirosis, etc. has been proven.

The parenteral route is implemented during medical procedures in which contact of instruments with blood is possible (hepatitis B, C, HIV viruses, etc.).

The transplantation path is implemented during organ transplantation (hepatitis B, C, HIV viruses, etc.).

The sexual route is realized through sexual contact (sexually transmitted diseases, HIV, hepatitis B virus, etc.).

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, chicken pox, 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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