species of the genus lentivirus, subgenus primate immunodeficiency viruses (immunodeficiency viruses, primate), that induces acquired immunodeficiency syndrome in monkeys and apes (saids). The genetic organization of siv is virtually identical to hIV. Siv is 50% homologous in nucleotide sequence to hIV-1. Siv and hIV-2 exhibit close structural and immunologic properties and are 75% homologous. Siv does not cause immune deficiency in its natural host, the african green monkey, but does produce saids in the rhesus macaque. Subgroups of siv include siv-1 and siv-2.