Liquid method of transmission of infection. The doctrine of the epidemic process. Types of vertical transmission of human diseases

Topic 2.

Epidemic process. Mechanisms and routes of transmission of infection. Anti-epidemic measures. Activities aimed at increasing the population's immunity to pathogens. The immune system human, immunity and its types. Nonspecific and specific human protection factors. Patterns of immunity formation in infectious diseases.

The founder of the doctrine of the epidemic process, Lev Vasilyevich Gromashevsky, was the first to develop in detail the theory of general epidemiology, the concept of the source of infection, the mechanism of transmission and the driving forces of the epidemic.

Epidemic process 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 of infectious diseases is the science of the patterns of occurrence and continuous development of the epidemic process and methods of its study, continuously developing and studying preventive and anti-epidemic measures, organizing their implementation in practice to prevent the occurrence infectious diseases among people, to stop these diseases if they occur and to completely eliminate certain infections in certain administrative territories and on a global scale.

The epidemic process determines the continuity of the interaction of its three elements:

1. Source of infection;

2. Mechanisms, pathways and factors of transmission;

3. Receptivity of the team.

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

Epidemic focus - the location of the source of infection with the surrounding territory to the extent that the infectious principle can be transmitted from it to surrounding persons, i.e. the development of an epidemic process is possible.

Source of infection - 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 the human body (patient or carrier), animal body and abiotic environmental objects.

· Anthroponoses are infections in which only humans serve as the source of infection.

· Zoonoses are infections in which sick animals serve as the source of infection.

· Sapronoses are infections in which environmental objects serve as the source of infection. (legionella - in air conditioner evaporators or shower units, yersinia - on rotting vegetables in vegetable stores). Microorganisms must multiply on environmental objects to provide a sufficient infectious dose, which must be very large, as in all cases with opportunistic microbes.

Mechanisms, routes and factors of transmission of infection.

Includes a sequential change of three stages:

· removal of the pathogen from the source organism in environment;

· presence of the pathogen in abiotic or biotic environmental objects;

introduction (introduction) of a pathogen into a susceptible organism

There are five main types of pathogen transmission mechanisms:

· airborne (aerogenic)

· contact

· transmission

fecal-oral (nutritional)

· vertical (including transplacental) (Gromashevsky)

Aerogenic mechanism of infection transmission- a mechanism of infection transmission in which pathogens are localized in the mucous membrane of the respiratory tract, from where they enter the air (when coughing, sneezing, etc.), remain there in the form of an aerosol and are introduced into the human body by inhaling contaminated air.

Contact mechanism of infection transmission- a mechanism of infection transmission in which pathogens are localized on the skin and its appendages, on the mucous membrane of the eyes, oral cavity, genitals, on the surface of wounds, from them onto the surface of various objects and upon contact of a susceptible person with them (sometimes through direct contact with source of infection) are introduced into his body.

Transmissible mechanism of infection transmission(also called “blood contact”) - a mechanism of infection transmission in which the infectious agent is in circulatory system and lymph, transmitted through the bites of specific and nonspecific carriers: the bite of a blood-sucking arthropod (insect or tick).

Fecal-oral mechanism of infection transmission- a mechanism of infection transmission in which the localization of the infectious agent mainly in the intestine determines its removal from the infected body with feces (feces, urine) or vomit. Entry into a susceptible organism occurs through the mouth, mainly through ingestion of contaminated water or food, after which it is reintroduced to the digestive tract of the new organism.

Vertical transmission route- in which the infectious agent is transmitted from mother to fetus during pregnancy and childbirth.

Types of vertical transmission of human diseases:

The development of medicine, new treatment technologies, and the deployment of a network of health care facilities have led to the formation of a new, artificial mechanism of infection transmission - artificial, which is associated with medical, primarily invasive, therapeutic and diagnostic procedures.

Transmission path - a form of implementation of the mechanism of transmission of infection from its source to a susceptible person (animal) with the participation of environmental objects.

Transmission factors - external elements environments (objects of inanimate nature) involved in the transmission of an infectious agent from a source to susceptible animals, but which are not the natural habitat of the agent.

• 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 there 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, they enter a new victim. This route of infection allows microbes to survive longer in the external environment.

Contact

This mechanism of infection transmission occurs through damage to human skin tissue or mucous membranes when there is direct contact (for example, touching) with 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?

Transmission mechanism intestinal infections 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).

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, healthy person it is transmitted 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. In this way they are transmitted venereal diseases, AIDS, frequency, some fungal diseases skin and some zoonoses. 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 items, 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 (flu, 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 products, 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 transmissible infections is a clear seasonality, which is associated with the period most active carriers. 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 when 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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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 frequency of vertical transmission from mother to child varies in different 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 method culture or PCR in fetal tissues starting at 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 results 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 those located in birth canal infected blood, secretions of the cervix and vagina; 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 breast-feeding; in contrast, in developing countries, breastfeeding plays a significant role in vertical transmission of HIV. U HIV-infected mothers, both free and cell-associated virus were found 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 transmitting 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 maternal CD4 cell count 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, since these data were obtained before the introduction of highly active antiretroviral therapy, the beneficial effect caesarean section, apparently, is insignificant if the concentration of viral RNA in the mother is less than 500 copies per 1 ml. Although a number of studies have documented an increased incidence of infection in women with late stage 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 had low (but detectable) viral RNA concentrations.

In infectious diseases, the pathogen can be transmitted in one or all four ways.

The larger the number; The number of ways a microorganism can be transmitted is the causative agent of infection, the more developed its capabilities are in preserving itself as a species. Usually one of the methods is the main one, and the rest are additional, occurring much less frequently.

Pathways of pathogen transmission. The emergence and development of IB is caused by the transmission of the pathogen through various MPs, in which distribution pathways play an important role. The routes of transmission (spread) of an infectious agent are the entire complex of factors involved in the transmission of an infectious agent under specific conditions in a certain space.

There are five horizontal and one vertical routes of transmission of the infectious agent:

Horizontal path. This is the most common (classical) method of transmission of the infectious agent, associated with its release into the external environment. The horizontal path is characteristic of the vast majority of infectious diseases, with environmental factors playing an active role.

Feed and water- typical transmission routes for nutritional infections, in which the animal becomes infected through the mouth with food or water, and excretes the pathogen in feces and urine.

In these cases, infection occurs:

Through feeders;

Water troughs;

Infected litter or soil;

Feed on pasture, as well as when giving infected milk or products of its processing (for tuberculosis, salmonellosis, brucellosis, foot-and-mouth disease, etc.);

Unneutralized slaughterhouse and kitchen waste (for swine fever, Aujeszky's disease, anthrax, salmonellosis, etc.);

When drinking water from natural sources (for leptospirosis, escherichiosis, salmonellosis).

Air route transmission is typical for respiratory or aerogenic infections, when the pathogen is transmitted through the air.

In this case, airborne infections arise as a result of penetration into Airways tiny droplets of mucus in case of damage to the respiratory system (sneezing, coughing, snorting), for example, with pasteurellosis, tuberculosis, sheep pox, contagious pleuropneumonia, influenza, ornithosis.

In airborne dust infections, the pathogen is transmitted by inhaling contaminated dust (anthrax, smallpox, tuberculosis, mycoses). The airway is important when animals are kept crowded in enclosed spaces, with insufficient ventilation, high humidity, low temperature (often found with infections in poultry farming, pig farming, etc.).

Transmission path characterized by the participation of vectors, primarily blood-sucking arthropods (insects or ticks). There are known infectious diseases transmitted exclusively by vector-borne means, the so-called obligately transmissible (infectious encephalomyelitis, African horse fever, arboviral infections), and diseases transmitted both by vector-borne and other routes, facultatively transmissible (infectious anemia, African swine fever, Siberian ulcer).

Carriers of pathogens of infectious diseases can also be non-susceptible or slightly susceptible animals and people (for anthrax - dogs, wild carnivores, birds of prey; for brucellosis - dogs; for Aujeszky's disease - rats, mice; for leptospirosis, listeriosis, tularemia - wild rodents) .

There are two types of transfer:

Biological (specific) - when the pathogen multiplies in the vector;

Mechanical - when there is no biological connection between the pathogen and the vector. The pathogen is transferred to the surfaces of the animal or human body, for example, on the clothing and shoes of personnel.

Contact path transmission can be divided into two types: transmission by direct contact (direct contact).

For example:

If bitten - rabies;

In case of mating - brucellosis or campylobacteriosis; when mothers suckle - infectious agalactia or Aujeszky's disease;

In case of contact - smallpox, foot and mouth disease, trichophytosis.

With such infections, the influence of the external environment on the transmission mechanism is insignificant; transmission by indirect contact (indirect contact).

In this case, the pathogen is transmitted through care items, service personnel and other factors.

The gates of infection through contact are the skin and mucous membranes of the eyes, nose, digestive or reproductive systems.

The soil route of transmission (some researchers do not distinguish it as an independent route, but refers to feed and water).

The pathogen is transmitted through the soil (in soil and wound infections); usually these are spore microorganisms that persist in the external environment for a very long time long time(causative agents of anthrax, emkar, malignant edema, bradzot, tetanus, infectious enterotoxemia and other clostridioses).

Animals become infected mainly by eating spore-contaminated feed (grass, hay, straw) or drinking from dirty ponds.

Vertical path. It is the transmission of a pathogen from parents to offspring without its release into the external environment.

The vertical transmission path is implemented:

Through the genetic apparatus; placenta;

Transovarial; with colostrum or milk;

For injuries of the birth canal.

Transmission factors. A prerequisite for the development of EP is the transmission of the pathogen through various infected objects in the external environment (transmission factors).

Transmission factors are all elements of the external environment (living and inanimate nature) that are involved in the transmission of the infectious agent, but are not their natural habitat.

The corpses of animals, especially those that died from diseases whose pathogens persist for a long time in the external environment (clostridium, erysipelas, tuberculosis, paratuberculosis, etc.) pose the greatest danger. That is why timely and proper cleaning and disposal of corpses is so important. Otherwise, you can contribute to the spread of the pathogen.

Manure is an important transmission factor for many diseases when the pathogen is excreted in urine and feces (foot-and-mouth disease, tuberculosis, colibacillosis, salmonellosis and many others).

Manure from infectiously diseased animals must be disinfected and, in some cases, burned.

Raw materials and livestock products, feed, in the absence of proper control, can become important factor transmission (foot and mouth disease, swine fever, African swine fever, anthrax, Aujeszky's disease).

Soil, premises, walking yards, playgrounds, contaminated pastures and livestock tracts can also serve as factors for the transmission of infections (clostridium, necrobacteriosis, hoof rot).

Equipment and care items, undisinfected instruments during veterinary treatments, containers, and transport are of significant importance in the transmission of pathogens of foot-and-mouth disease, smallpox, swine fever, etc.

The spread of diseases can be facilitated by the accumulation of animals in markets (bazaars), fairs, exhibitions, hippodromes, meat processing plants, railway stations, ports, etc.

In conclusion, we can say the following. The mechanism of transmission of infectious agents is very diverse.

During anti-epizootic measures, it is of great importance to identify it (methods, ways, factors) and eliminate it as one of the links in the EC - rupture of the EC.

Susceptible organism (3rd link of the epizootic chain). Susceptible animals (SA) are the third mandatory link of the EC, ensuring the continuity of the EP.

Susceptibility (the opposite of resistance or resistance) is one of the most important epidemiological categories. The susceptibility of an organism is the ability of an animal to become infected and become ill with an infectious disease.

But since the epizootic process affects the population (herd), then from an epizootological point of view, it is not so much the individual susceptibility (of an individual animal) that is important, but rather the susceptibility of the population, or group susceptibility, which, depending on varying degrees The susceptibility of individual animals can vary significantly.

For example, to foot-and-mouth disease, rinderpest, and anthrax, the corresponding animal species are almost 100% susceptible, but for most diseases the susceptibility is lower and some animals do not get sick. This is due to the immune heterogeneity of the population.

The degree of susceptibility in epizootology is indicated by the contagiousness index, which is expressed as a percentage. Index 100 corresponds to 100% susceptibility of animals.

A high index of contagiousness indicates high susceptibility, and vice versa (for example, with plague or foot-and-mouth disease, the contagiousness index reaches 100%, with listeriosis - 20...30%, with infectious rhinotracheitis varies widely - from 5 to 95%, with bluetongue it is 50...60%).

Immunological structure of the herd- this is the ratio in a group (herd, population) of the number of susceptible and non-susceptible animals.

Many factors influence the susceptibility of animals to certain diseases:

Age;

Physiological features;

Feeding;

Operating mode;

Factors of external and internal environment;

Natural nonspecific resistance;

Emerging immunity;

As a result of the interaction of physiological, functional, nonspecific and specific factors, group susceptibility or immunity of the livestock is formed.

The latter received an inaccurate name - “population (or herd) immunity”, which has an important influence on the manifestation and course of EP. It is stronger the more complete and correct the organizational, economic, veterinary, sanitary and special (specific) measures are.

Epizootic focus - in accordance with modern concepts, the following definitions of an epizootic focus can be given.

Epizootic focus (EO)- the place of interaction of all three links of the epizootic chain.

Epizootic focus- the location of the source of the infectious agent among the animal population in the territory where its transmission to susceptible animals and the spread of the disease are currently possible.

EO is an elementary cell of EP; it can be attributed to all infectious diseases, regardless of the degree of their distribution (sporadia, epizootic, panzootic). EO - can vary in size, that is, in the number of sick animals (from a small personal farmstead with one sick animal to a large livestock complex with adjacent pastures and territories).

The importance of EO is not in its size, but in the fact that this is the place where the “light” of IB arose, is supported and can spread (the word hearth arose from the Turkish “osag” - light). As long as the outbreak remains active, the danger of the spread of cybersecurity remains.

Elimination of EO consists of neutralizing sources of infectious agents, disinfecting environmental objects and excluding susceptible animals from the EC.

Epizootic foci are divided into four groups depending on the time factor, connection with the area and a specific animal species.

Types of epizootic foci

By time: Fresh EO - recently arisen as a result of the introduction of a pathogen from the outside, with an increase in the number of cases of infection and disease in animals. The risk of the disease spreading increases. Decaying EO - in which h decreases

the number of cases of isolation of patients (during anti-epizootic measures or naturally) and the danger of spreading the disease.

By area: Stationary EO - in which outbreaks of the disease are repeated or can be repeated at various intervals due to the persistence of the conditions for their occurrence (for example, the long-term persistence of the anthrax pathogen in the soil or the presence of microbial carriers in the herd for other diseases).

By animal species: Natural EOs - in which the pathogen infectious disease circulates in a certain territory among wild animals permanently living there.

The peculiarity of a stationary outbreak is that at the moment there may be no IVI, although the pathogen persists in the external environment (anthrax, botulism, etc.).

This condition is not permanent, although it can last for quite a long time.

The occurrence of EO can be associated either with an individual case or with an outbreak of the disease. In this case, the term IB case denotes a disease of one animal; an IB outbreak characterizes the almost simultaneous occurrence of several cases of IB at a point (farm).

Thus, the case and the outbreak of IB serve as quantitative characteristics of the manifestation of EP in the EO.

In the official veterinary reporting (veterinary statistics) on infectious diseases in Kazakhstan (form “1-vet”) the concepts “number of sick animals” and “number of unfavorable points” appear.

At the same time, statistical designations are identical to epizootic ones, since the number of sick animals is equal to the number of cases of the disease, and the number of unfavorable points is equal to the number of epizootic foci.

Unfavorable point (NP)- administrative-territorial unit (settlement or livestock breeding facility), on the territory of which an epizootic focus was discovered.

A city district or an entire city, village, farm, farm, department, brigade, farmstead, etc. can be declared a disadvantaged area.

The boundaries of the NP are set depending on the isolation of the NP from other points and the nature of the disease that has arisen.

For example: in a large village several farms are located at some distance from each other.

If highly contagious foot-and-mouth disease occurs on one of the farms, the entire village will be considered OP, and anthrax - only this farm will be declared OP.

Control questions

1. What is IVI?

2. Source of the infectious agent (1st link of the epizootic chain)?

3. Source of the infectious agent (2nd link of the epizootic chain)?

Factors determining the intensity of EP. The intensity of manifestation (tension) of ED depends on many factors. Among them are:

Biological (virulence of the pathogen, infectious dose, degree of susceptibility of animals, forms of manifestation of the disease, etc.);

Natural-geographical (presence and density of vectors, season of the year, presence of natural reservoirs, etc.);

Economic, or economic (density of animals, mode of their operation, economic relations, zoohygienic condition of premises, quality of veterinary care, etc.).

Degree of manifestation of EP. The listed factors determine the degree of manifestation of the disease - from a single case to mass destruction of animals. In epizootology, the intensity of EP is characterized using the following scale:

Sporadia, sporadic morbidity, sporadic cases (Greek sporadicos - from case to case, single) - the lowest degree of intensity of EP, characterized by isolated cases of the disease, between which it is not possible to trace an epizootic connection, that is, animals become ill as if independently of each other ( for example, tetanus, rabies, catarrhal fever, etc.).

Epizootic (epi - above, zoon - animal) - an average degree of intensity of epidemic, characterized by a fairly wide spread of the disease with a tendency to increase the number of cases of the disease in a certain territory; As a rule, a common source and mechanism of transmission are identified (most infectious diseases).

Panzootic (pan - all, zoon - animal) is the highest degree of intensity of EP, characterized by an unusually wide spread of the disease - over entire countries and continents (for example, foot and mouth disease, rinderpest, contagious bovine pleuropneumonia, ASF, etc.).

It is worth noting some features of the degrees of EP intensity. In many cases, sporadia is only a precursor to a mass outbreak of the disease (during the inter-epizootic period).

In an epizootic, an epizootological connection must be visible between individual cases. The main factors characterizing the epizootic include:

The mass factor is the defeat of a large number of animals;

Spread factor - a tendency to expand the area (spread) of the disease;

Territoriality factor - covering a large territory; the time factor is the speed of spread.

Panzootic disease is characterized by a sharp and rapid increase in incidence associated with the extraordinary contagiousness of some infectious diseases.

The boundaries between sporadic, epizootic and panzootic are arbitrary and not constant, which depends on the level of incidence usual for a given region (background, average incidence over many years), the danger of the disease, its exoticism for the country and other factors.

Enzootic. In epizootology, another term is used to characterize EP - enzootic (enzootic), which has nothing to do with the intensity of EP.

Enzootic or enzootic(en - in, zoon - animal) - the presence (spread) of an infectious disease in a certain area (farm, point). Enzootics can manifest themselves in the form of sporadia and epizootics.

Control questions

1. Degree of manifestation of ED.

2. What is Enzootic, or enzootic?

3. What are the main factors characterizing an epizootic?