Human Immunodeficiency Virus Type 2
In virology, Human Immunodeficiency Virus Type 2 (HIV-2) is an "HIV species related to HIV-1 but carrying different antigenic components and with differing nucleic acid composition. It shares serologic reactivity and sequence homology with the simian Lentivirus simian immunodeficiency virus and infects only T4-lymphocytes expressing the CD4 phenotypic marker."
HIV-2 is thought to have originated by zoonotic transfer to humans from simian immunodeficiency virussooty mangabey (Cercocebus atys) in the Guinea-Bissau region of coastal West Africa during their independence war (1963–1974). 
- Anonymous (2015), Human Immunodeficiency Virus Type 2 (English). Medical Subject Headings. U.S. National Library of Medicine.
- Lemey P, Pybus OG, Wang B, Saksena NK, Salemi M, Vandamme AM (2003). "Tracing the origin and history of the HIV-2 epidemic.". Proc Natl Acad Sci U S A 100 (11): 6588-92. DOI:10.1073/pnas.0936469100. PMID 12743376. PMC PMC164491. Research Blogging.