The HIV genome contains accessory and regulatory genes flanked by long terminal repeats (LTR). The core contains two 9.8-kb long positive sense, single stranded, linear RNA molecules, molecules to initiate cDNA synthesis, cellular tRNA, Gag polyprotein, viral envelope (Env) protein and three enzymes: reverse transcriptase (RT), viral protease (PR), integrase (IN), and some other cellular factors ( 10, 11). Mature HIV virions are 100–120 nm in diameter spherical structures consisting of a lipid bilayer membrane which encloses a dense truncated cone-shaped nucleocapsid (core). According to the survey report of UNAIDS (2015), globally about 36.7 million people suffered from HIV infection and among them approximately 2.1 million new HIV infections were reported ( 8). This is largely because people on antiretroviral therapies are living longer than before, while the global incidence has reduced by approximately 1 million from 2002 to 2012 ( 7). There has not been a significant increase in the prevalence of HIV globally, with 31 million cases reported in 2002 to 35.3 million cases reported in 2012. However, increasing access to antiretroviral therapies has significantly improved the global epidemiology of HIV infection. In 2012, approximately 35.3 million individuals were living with HIV, with the highest global burden of HIV (70.8%) in Sub-saharan Africa ( 6). Subtype B of HIV-1 dominates in Australia, Americas, and Europe, whereas subtype C predominates in India and Africa (which accounted for 48% of all the HIV-1 cases in 2007). These recombinants are called CRFs if they have a significant epidemic spread. Subtypes and sub-subtypes are a result of founder effects at various time periods in the past, whereas if two different subtypes co-infect a patient it gives rise to the inter-subtype recombinants. There are nine known phylogenetic subtypes, sub-subtypes of Group M, clades (A–K) and an inter-subtype circulating recombinant forms (CRFs) among which inter-subtype genetic diversity is 25% for the env gene and 15% for the gag gene. Group M of HIV-1 is the major cause of worldwide HIV epidemic. In 2005, AIDS-related deaths peaked to 2.3 million globally, but reduced to 1.6 million by 2012 ( 5). In 2010, HIV was the fifth leading cause of disability-adjusted life years in people of all ages, and leading cause for people aged 30–44 years. Human immunodeficiency virus is the chief contributor to global burden of disease. A detailed investigation on HIV structure and its mechanism of infection have not only allowed to characterize and develop new and effective vaccines and drugs but has also described new approaches for diagnosis of HIV at the laboratory scale ( 2). On the other hand, HIV-2 is only constrained to some areas of Central and Western Africa ( 2). Among these strains, HIV-1 is the most virulent and pathogenic, and when people normally talk about HIV without stating the type of virus they are referring to HIV-1 ( 4). Two types of HIV have been isolated and characterized from patients infected with the virus: HIV-1 and HIV-2. Since then, virology of HIV and pathogenesis of infection are constantly being studied. Initial cases of HIV were reported in 1981 to Centre for Disease Control, and the virus was first isolated from patients with severe immune deficiency, later termed as Acquired Immune Deficiency Syndrome (AIDS), in 1983 ( 3). HIV is classified as a member of the family Retroviridae and genus Lentivirus based on the biological, morphological, and genetic properties ( 2). Many of the epidemiological, phylogenetic, and genomic characteristics of HIV are similar to those of SIV, and this strongly supports the idea of cross species transmission ( 1). Human immunodeficiency virus (HIV) originates from a monkey infecting virus, simian immunodeficiency virus (SIV), and a number of theories have been described in this regard. Invention of CRISPR/Cas9 is a breakthrough in the field of HIV disease management. Antiretroviral therapy and vaccines are promising candidates in providing therapeutic and preventive regimes, respectively. The diagnostic techniques like PCR, rapid test, EIA, p24 antigen, and western blot have markedly upgraded the diagnosis of HIV. Advanced diagnostic methods are exploring new ways of treatment and contributing in the reduction of HIV cases. Among these strains, HIV-1 is the most virulent and pathogenic. It infects different cells of the immune system, such as CD4+ T cells (T-helper cells), dendritic cells, and macrophages. It is classified as a member of the family Retroviridae and genus Lentivirus based on the biological, morphological, and genetic properties. In 2010, HIV was the fifth leading cause of disability-adjusted life years in people of all ages and leading cause for people aged 30–44 years. Human immunodeficiency virus (HIV) is the chief contributor to global burden of disease.
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