In 1983 the French Cancer specialist Luc Montagnier and his fellow researchers working at the Pasteur Institute identified a new human retrovirus from patients suffering from AIDS. They named it as Lymphadenopathy virus (LAV). Some eight months later Gallo and his fellow researchers identified and isolated the same virus from AIDS patients and named it as HTLV-III. Later scientists came to an agreement and termed the virus HIV. In 1985 a new virus that had the potency to cause AIDS was identified in some of the West African nations. It was termed as HIV-2. Its close resemblance to HIV-1 and its comparatively lower potency become evident from the remark made by Bartlett (2003),
On the genetic scale HIV-1 contains Simian immunodeficiency virus (SIV) sequences from chimpanzee where as HIV-2 contains SIV sequences from Macaque/Sooty Mangabey. According to the article "Origin of HIV-1 and HIV-2: Cross species transmission of SIV to human." (n. d),
"This indicates that HIV-1 originated from one event where a virus was transmitted from (presumably) chimpanzees to humans, while HIV-2 originates from a second, independent event where virus was transmitted from (presumably) sooty mangabey to humans."
When HIV is present outside the human cells it exists in the form of independent particles termed as virions. ...