THE ORIGIN OF HIV
Two distinct viruses that causes AIDS in humans, HIV-1 and HIV-2. Of the two, HIV-1 is the virus primarily responsible for the global HIV epidemic, while HIV-2 is more geographically restricted . HIV-1 can further be divided into three groups; M (main), N (non-M, non-O) and O (outlier).
The M group is the cause of the global epidemic, and can be further divided into subtypes (A, B, C, D, F, G, H, J and K), circulating recombinant forms (CRF) and unique recombinant forms (URF). Compelling phylogenetic evidence demonstrates that HIV-1 and HIV-2 originate from simian immunodeficiency virus (SIV) in African non-human primates.
The natural reservoir of HIV-1 is the chimpanzee subspecies Pan troglodytes troglodytes which harbors the closely related SIVcpz virus that has, with the possible exception for group O, been transmitted to humans as HIV-1. These primates are found in southern Cameroon, and this region since the origin of hiv is considered as the epicenter of the HIV-1 epidemic. Although both HIV-1 and HIV-2 can cause immunodeficiency, HIV-2 has a lower transmission rate and is less virulent compared to HIV-1 and does not cause AIDS in all infected individuals.
The earliest known case of HIV-1 was retrospectively identified in a plasma sample obtained in 1959 in Leopoldville, now Kinshasa, in the Democratic Republic of Congo. However, since the origin of the hiv, even if virus was present in humans as early as the year 1900, the epidemic did not pick up speed until later in the century.
Several possible factors may have contributed to the acceleration of the HIV-1 epidemic since THE ORIGIN OF HIV; increased travel, urbanization, enslavement, prostitution and societal disruption in the beginning of the century have been proposed to have facilitated the spread of the epidemic. In addition, the increased use of injections using unsterile medical equipment during medical treatment or vaccination campaigns may have promoted viral adaptation to the human host by serial passage in humans.