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The basic conditions necessary for the occurrence of an infectious disease

For the occurrence of an infectious disease, three prerequisites are necessary: ​​the source of infection, the mechanism of transmission of infection and the susceptibility of the human body.

1. Sources of infection:

Sick person - refers to the most dangerous sources of infection, because it excretes in a large number of pathogens, moreover, in the most virulent state. Of particular danger are patients with atypical, erased forms of the disease, because they can be in contact with others for a long time, infecting them and environmental objects, including food products.

Sick animal - can be both a direct danger and the transmission of the pathogen through the "food chain" through food products received from it.

Infection carriers (bacterio-, virus- and parasitic carriers) - carriage often occurs after the transmission of infectious diseases, when both humans and animals release pathogens into the environment for some time.

2. The mechanism of transmission of infection is the evolutionarily acquired ability of microorganisms to spread from the source of infection to susceptible macroorganisms. A transmission mechanism is being implemented using pathways and transmission factors of infection.

Infection transmission factors are environmental elements that may be involved in the spread of disease pathogens. These include water, soil, air, food, household items, apparatus, equipment, containers, packaging, dishes, etc. Transmission factors determine the transmission of infection.

A contact transmission path is transfer through contact. There are direct contact - transmission of infection with direct contact of the skin and mucous membranes with the source of infection and indirect - through household and industrial items.

Airborne transmission - infection is transmitted through the air through an airborne droplet (the pathogen is transferred with droplets of mucus released from the respiratory tract of the patient or carrier) or by airborne dust (through infected dust).

Waterway - when drinking contaminated water, bathing in it, using it for industrial and household needs, for washing vegetables, dishes, equipment, etc.

The food route - differs from those listed above in that food products can not only transmit the infection, but also serve as a favorable breeding ground for the reproduction and accumulation of microbes. Food contamination occurs in various ways:

• directly from a sick animal from which this product is obtained (milk, meat, eggs);

• from a sick person or a carrier carrier when processing products, through equipment, utensils, water, air, hands, etc.

The transmissible path is the path of transmission through the bites of insect vectors (mosquitoes for malaria, ticks for tick-borne encephalitis, lice for typhus, etc.). In this case, the pathogen enters directly into the blood.

Depending on the factors and transmission routes, four mechanisms of transmission of pathogens are distinguished, according to which all infections are also divided into four groups:

• airborne droplet (aerosol) mechanism - transmission of infections of the upper respiratory tract and lungs;

• fecal-oral mechanism - the transmission of intestinal infections by food, water and the household;

• contact mechanism - transmission of infections of the external integument (skin and mucous membrane diseases);

• transmission mechanism - transmission of blood (vector-borne) infections.

Susceptibility of an organism - the ability of the human body to become ill when meeting a pathogen. Refractory persons may not become ill when in contact with infected objects or directly with patients or carriers.

The susceptibility of an organism is determined by resistance and immunity.

Resistance - this is nonspecific stability of the body, due to the action of general protective factors (conditions of nutrition, labor, life, rest, climate, social conditions, economic opportunities, etc.).

Non-specific protection factors play an important role in protecting the body against infectious disease pathogens: impermeability of the skin and mucous membranes for most microorganisms; the presence in the skin secret and acidic contents of the stomach of substances that adversely affect microorganisms; the presence in the blood and body fluids (saliva, tears, etc.) of enzyme systems that destroy microorganisms (lysozyme, etc.), etc.

Immunity is the specific resistance of an organism to infection. Specific immunity determines protection against only one infection and does not affect the susceptibility to other infections. Distinguish between natural and artificial immunity.

Natural immunity can be congenital (inherited) and acquired (as a result of an illness). Acquired immunity can be short-term, long-term or lifelong.

Artificial immunity - created artificially by introducing various drugs into the body. There are two types of artificial immunity:

• artificial active immunity - vaccines and toxoids (vaccine prophylaxis) are used to create it. Currently, there are two categories of vaccines: traditional (live, inactivated, i.e. killed and chemical vaccines) and new generation vaccines (synthetic, genetically engineered, etc.).

• artificial passive immunity - immune serums and immunoglobulins are used to create it (seroprophylaxis).

Thus, if at least one of the three links — the source of infection, transmission routes, and susceptibility of the population — is excluded from the epidemic chain, the pathogen’s circulation ceases and the disease does not spread further. This is the basis for the prevention of infectious diseases, including those transmitted through food products.
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