Causes of HIV infection / AIDS

The causative agent of HIV infection. The human immunodeficiency virus (HIV) belongs to the family of retroviruses (Retroviridae). The family of retroviruses includes two subfamilies - oncoviruses (Oncoviridae) and slow lentiviruses (Lentivirus). The first subfamily includes viruses that cause leukemia: T-cell leukemia and chronic hairy cell leukemia, as well as the bovine leukemia virus.

HIV belongs to the subfamily of lentiviruses. Currently, 7 types of lentiviruses are known, of which 6 are pathogenic for animals and only one (HIV) causes disease in humans.

Currently, 3 serotypes of the virus have been described: HIV-1, HIV-2 and SIV, which differ in structural and antigenic characteristics. Of greatest epidemiological significance is HIV-1, which dominates the current pandemic and is most widespread in Europe, including Ukraine. HIV-2 is found mainly in West African countries.

HIV virions are round in shape with a diameter of 100-120 nm. The viral particle is a conical core surrounded by an envelope. HIV belongs to the class of retroviruses, which suggests the transfer of genetic information in virions in the form of RNA. In the structure of the viral particle, the central part of the retrovirus, in addition to two copies of the positive RNA chain, contains DNA-binding proteins and reverse transcriptase used to translate the viral RNA into DNA for its subsequent integration into the genome, as well as transcription of the viral DNA by the eukaryotic cell apparatus.

Of fundamental importance is the structure of the membrane, which is a fragment of the host cell membrane. In the lipid layer of the membrane, glycoproteins with a molecular weight of 160 kilodaltons (Kd), gp 160, are localized, which play a key role in the mechanism of "recognition" and penetration into the target cell. The glycoprotein consists of an external (epimembrane) part with a molecular weight of 120 Kd (gp120) and a transmembrane part of -41 Kd (gp41).

The core membrane contains a protein with a molecular weight of 24 kDa (p24). Between the outer membrane of the virion and the nucleoid there is a framework consisting of a matrix protein of 17 kDa (p17). The nucleoid contains two single-stranded RNA molecules, a complex of enzymes (reverse transcriptase (revertase), integrase, RNase H, proteinase) and genes responsible for the production of membrane proteins, enzymes and nuclear structures.

The limited size of RNA synthesis places high demands on the saturation of the genetic material contained in the virus. Typically, the retroviral genome does not exceed 10 kbp in length.

The HIV genome consists of 9 genes: 3 of them are structural, characteristic of all retroviruses, and 6 are regulatory. One of the regulatory genes (nef) slows down the transcription of viral genomes. The synchronous function of two genes (nef and tat) ensures replication of the virus without causing the death of the cell infected with the virus.

In addition, HIV is characterized by exceptionally high genetic variability. Like all retroviruses, HIV is characterized by high variability in the human body; as the infection progresses from asymptomatic to manifest, the virus evolves from a less virulent to a more virulent variant.

Under natural conditions, HIV can survive in a dried biosubstrate for several hours, in liquids containing a large number of viral particles (blood, ejaculate) - for several days, and in frozen blood serum, the activity of the virus persists for up to several years. The low concentration of HIV in other biological fluids determines its rapid inactivation.

HIV is not stable in the external environment. Heating to a temperature of 56°C for 10 minutes leads to a 100-fold decrease in the infectious titer of the virus, at 70° -80°C the virus dies after 10 minutes. The virus dies with a sharp change in the reaction of the environment (pH below 0.1 and above 13), as well as under the influence of disinfectants in concentrations commonly used in laboratory practice (70% ethyl alcohol, 6% hydrogen peroxide solution, 0.5% sodium hypochlorite solution, 1% glutaraldehyde solution, 5% lysol solution, ether, acetone).

The source of HIV is a person at all stages of the disease. The virus is found in blood, sperm, cerebrospinal fluid, breast milk, menstrual blood, vaginal and cervical secretions. In saliva, tear fluid, urine, the virus is in small quantities, insufficient for infection.

Routes of HIV transmission

There are sexual, parenteral and vertical routes of HIV transmission.

Sexual transmission of the infection is realized during hetero- and homosexual sexual contacts. The probability of infection increases with inflammatory diseases of the genitals. It is believed that the share of sexual transmission of the virus currently accounts for more than half of all cases of infection. The ratio of infected men and women has changed over time: at the beginning of the epidemic - 5:1, then 3:1, now this figure is approaching 2:1.

Parenteral infection is mainly found among drug addicts who inject drugs intravenously. HIV transmission factors can be shared syringes and needles, as well as the drug itself. Infection is possible through transfusions of infected blood, its preparations, organ and tissue transplants, and the use of HIV-contaminated medical instruments.

Vertical transmission of HIV occurs from an HIV-infected woman to her child during pregnancy and childbirth, as well as during breastfeeding from an infected mother to her child and from an infected child to a nursing woman. In the absence of prevention of perinatal transmission of HIV, the risk of HIV infection is 30-40%. The probability of infection of a child during breastfeeding is 12-20%.

Contact-household, airborne transmission routes for HIV infection have not been described. Blood-sucking insects do not play a role in the spread of infection.

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