HIV (Human Immunodeficiency Virus)
Type 1 and Type 2 (HIV-1 and HIVE-2 ) have been described as the etiologic agents of Acquired Immunodeficiency Syndrome (AIDS). AIDS is the end stage of virus mediated protracted pathogenic process in which the immune system of an infected person and its ability to control infections or malignant progressive disorders are progressively destroyed (Schupbach J, 2003 ). AIDS was first recognized in United States in 1981 with a sudden outbreak of opportunistic infections, Pneumocystis carinii pneumonia and Kaposi’s sarcoma (Gottlieb et.al., 1981).
HIV-1 is the third retrovirus to be discovered. HIV-1 was discovered by Barre-Sinoussi, 1983 and after one year it was proved to be virologically and serologically associated with early and latent stage of AIDS
HIV-2 was the fourth retrovirus to be discovered in 1986 from patients in Western Africa. HIV-1 has shown to be more aggressive virus and is mainly responsible for current AIDS pandemic whereas HIV-2 has been described as less pathogenic (Schupbach J, 2003). The rates of heterosexual and mother to child transmission of HIV-2 has been reported to be low, and the infection seems to be more latent and this virus has been reported to cause AIDS very rarely (Schim van der Loeff, 1999).
HIV is enveloped, positive sense, RNA virus with diameter of about 110 nm (90-120 nm). The virions bud from the host cell membrane forming a sphere with an outer lipid bi-layer and a nucleocapsid with a dense cone shaped core. It has been reported that the core appears to be attached with the viral outer envelope at its narrow end, The mature virus consists of a bar-shaped electron dense core containing the viral genome- two short strands of ribonucleic acid (RNA) about 9200 nucleotide bases long, along with the enzymes reverse transcriptase, protease, ribonuclease, and integrasee, all encased in an outer lipid envelope derived from a host cell. Eash HIV-1 viral particles contains 71 glycoprotein complexes, which are integrated into this lipid membrane, and are each composed of trimers of an external glycoprotein gp 1220 and a trans-membrane spanning protein gp41. The bonding between gp120 may be shed spontaneously within the local environment. Glycoprotein gp120 may also be detected in the serum as well as within lymphatic tissue of HIV-infected patients. During the process of budding, the virus may also incorporate different host proteins from the membrane of the host cell into its lipoprotein layer, such as HLA class I and II proteins, or adhesion proteins such ass ICAM-1 that may facilitate adhesion to other target cells. The matrix protein p17 is anchored to the inside of the viral lipoprotein membrane. The p24 core antigen contains two copies of HIV-1 RNA. The HIV-1 RNA is part of a protein-nucleic acid complex, which is composed of the nucleoprotein p7 and the reverse transcriptase p66(RT). The viral particle contains all the enzymatic equipment that is necessary for replication: a reverse transcriptase (RT), an integrase p32 and a protease p11 (Gelderblom, 1993)