Human Immunodeficiency Virus
HIV is a lentivirus (a member of the retrovirus family) differentiated on structural and antigenic properties into two virus types: HIV-1 and HIV-2. HIV-2 occurs considerably less often than HIV-1. In accordance with 1991 Nomenclature, there are three independent HIV-1 groups: M (main); O (outlier); N (non-V/non-O). In addition to this, there are the so-called "circulating recombinant forms (CRF)" viruses with a mosaic structure of the genome, elements of which are typical for representatives of various subtypes. Groups O and N are less widely spread and occur in African countries population. Group M includes 11 subtypes: A1, A2, B, C, D, F1, F2, G, H, J, K. Transmission ways of the virus are very important for the virus spread. HIV is transmitted by three ways: at heterosexual and homosexual sexual intercourse, parenteral with blood and blood products and vertically: from the infected mother to the child by an intrauterine way, during the child delivery or soon after the childbirth at breast feeding.