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The emergence and spread of various microbial diseases is due to the fact that some microbes under certain conditions can acquire the properties of pathogens. These are the so-called pathogenic microorganisms. Pathogenic microorganisms can cause various diseases, including infectious ones. It is known that pathogenic microorganisms are characterized by strict specificity, i.e., each specific pathogen causes only a specific disease. The main difference between infectious diseases and other diseases is that they can be transmitted from a sick person to a healthy one and, under certain conditions, affect large groups of people. It should be recalled that food poisoning, in contrast to infectious diseases, is not transmitted from a sick person to a healthy one.

Pathogenic microbes can produce two types of toxins, which also have a pathogenic effect on the human body:

a) exotoxins - are released into the environment during the life of microorganisms;

b) endotoxins - released into the environment after the death of microorganisms.

Human infectious diseases can take three forms:

1. With a disease, the physiological functions of the body are violated, and the body is brought out of equilibrium with the environment, that is, an infectious disease develops, and the signs of the disease appear sharply;

2. The symptoms of the disease do not appear sharply and, as a rule, a person transfers such diseases, as they say, “on his feet”, such forms of the disease are “atypical” or “erased”;

3. There are no signs of the disease at all, and this form of interaction between a person and a microorganism is a “hidden” infection, which is sometimes called a healthy carrier.

It is known that when an infectious disease occurs, not all people in a particular team get sick. This is due to the fact that with high immunobiological reactivity (resistance) of the body, the pathogenic microorganisms that enter it die, and the disease does not occur. Conversely, when microorganisms find favorable conditions for their existence in the human body, then an infectious disease occurs.

In general, for an infectious disease to occur in a team, three prerequisites are necessary:

1) There must be a source of infection;

2) There must be certain ways of spreading the infection;

3) There should be a susceptibility of the population (team) to this infectious disease.

It should be noted that the exclusion from this epidemiological chain of at least one of these links does not lead to the occurrence of an infectious disease.

Sick people and animals can be a source of infection for humans. If only people are the source of infection, then such diseases are called anthroponoses. If only animals are the source of the disease, then such diseases are called zoonoses. If the source of this infectious disease can be both animals and people, then such diseases are called zooanthroponoses.

It should be noted that in addition to patients with a certain infectious disease of humans and animals, bacteria carriers may also be a source of infection, i.e. people or animals who have had a certain infectious disease, but who for a certain time have been releasing microorganisms into the environment that cause the infectious disease.

2. The route of transmission of infection depends on the location (localization) of the causative agent of the infectious disease. And in this regard, there are four types of transmission mechanisms:

a) fecal-oral (localization of the pathogen in the intestine);

b) drip (localization of the pathogen in the respiratory tract);

c) transmissible, or transmission of infection by blood-sucking vectors (localization of the pathogen in the circulatory system);

d) contact - transmission of the pathogen through household and industrial items or by direct contact (localization of the pathogen on the skin and mucous membranes)

Depending on the transmission factors of the infectious disease, there are water factors, food, airborne, soil, household, etc.

3. The third prerequisite for the occurrence of an infectious disease is the susceptibility of the population to this disease, that is, the person's resistance to the disease when meeting with a pathogenic pathogen. It should be noted that the lower the susceptibility of the population to this disease, the less intense the nature of the epidemic.

Prevention of infectious diseases is reduced to the following main areas:

1- Carrying out government measures aimed at eliminating the causes that contribute to the emergence and spread of infectious diseases (improving working conditions, life, public services, etc.);

2- Raising the level of sanitary culture of the population;

3- Carrying out medical measures (isolation of an infected person, sanitary control over the cleaning of settlements, water supply, sewage, compliance with the sanitary regime at catering, trade, child care facilities, vaccination, and others).
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