Human viral diseases are the result of exposure to the smallest life forms - viruses.
Viruses and viral diseases are carriers of genetic information - nucleic acid molecules surrounded by a dense protective shell of proteins. Being outside the cell, viruses show no signs of life and behave like organic particles of polymers. Simple in structure, without a cellular structure, pathogens can live only in living cells of the human body, animals, plants and in fibroblasts of the chicken embryo. Invading the cells of the human body , the virus begins to actively feed on the contents of the cell, which ensures its quick death.
According to the epidemiological characteristics, human viral diseases are divided into zooanthroponic ones that are transmitted to humans from animals, and anthroponic ones that only a person can get sick. The main ways in which viral infections are transmitted to humans are:
- food route - viral hepatitis A and E are transmitted with contaminated food and water;
- through the blood or parenteral route is the transmission of fragile viruses that are rapidly destroyed in the environment. These are rabies, hepatitis B, HIV and other viruses. Transmission occurs during unprotected sexual contact, when working with infected surgical instruments, and transplacental from mother to fetus;
- viral infections of influenza, mumps and chicken pox are transmitted through the respiratory tract. This path is most dangerous, since viruses are carried over a considerable distance with air, and can cause epidemics.
Each type of virus in the human body has target organs that are more suitable for the development of a particular viral infection. By the type of organs affected by viruses, the types of viral infections are distinguished: respiratory, intestinal, affecting the peripheral and central nervous system. Viruses infect the skin and mucous membrane, internal organs, the immune system and blood vessels of the human body.
Viral diseases, the types of their clinical development are divided into acute and chronic.
The acute disease occurs with fever, pain in the muscles and joints, weakness and a change in blood composition. When examining a patient, local symptoms are also revealed - damage to the brain zones, damage to the liver and mucous membrane of the respiratory tract. Acute diseases are easily amenable to medical treatment. Correct and timely treatment of the patient will prevent the transition of the disease into a chronic form.
Another picture of the course of the disease with a chronic form of viral infection. The disease usually proceeds unnoticed, human viral diseases of this nature are difficult to treat and can last a long time, which leads to functional changes in the internal organs.
Latent infection, which may be present for a long time in the patientβs body with the complete absence of symptoms of a viral disease, also refers to dangerous infections. It is this kind of infection that can be activated and go into acute form under any influence of an internal or external factor, for example, a decrease in immunity or hypothermia of the body.
At the place of localization, infection can be local and generalized.
Human viral diseases are local in nature if the virus multiplies at the site of infection and does not spread throughout the body. Generalized infections, after primary reproduction at the site of penetration, penetrate further into the blood and are carried by the bloodstream to various organs.